Re: PDP 11 gear finally moved
Hi all, Question to the group...not a vintage computer problem. A problem with a much newer system. An Acer Aspire desktop about 10 years old. I'm trying to sell it and reset windows (vista) to factory original. It locked up'd during that process and I reset it. Seems the BIOS is now corrupted. I need to re-flash the BIOS and to do that I need a bootable CD disk. I have tried several times to format a brand new disk and make it a boot disk. Problem is the format option under Windows 8 doesn't allow me to click that make boot disk option. Any ideas on how to create a boot disk for a windows vista system? Once I have the boot disk, it's a simple matter to copy the BIOS files to that disk and re-flash the system. Once it is started again, I can see what's up with the original Vista or whether i need to do a full re-load. I would like any ideas anyone has to offer. I have lots of computer gear and need to "cull the heard", too much space and I'm moving soon. I hate to see a buyer slip away. You can email me directly at _local52mixer@aol.com_ (mailto:local52mi...@aol.com) _or_ (mailto:local52mixer@or) call my cell...732-530-1924. Thanks in advance, BD In a message dated 7/24/2015 1:18:09 A.M. Eastern Daylight Time, tothw...@concentric.net writes: On Wed, 22 Jul 2015, Chuck Guzis wrote: > On 07/22/2015 10:09 PM, Tothwolf wrote: > >> One example I can give are some Pentium P55C architecture (Socket 7) >> systems which I've been running with minimal downtime for ~15 years. >> The original power supplies with their original (and relatively low >> quality) capacitors lasted about 15 to 17 years (I think the >> manufacture date code stamped on the oldest one was 1998) before the >> systems began to develop stability issues, requiring me to rebuild the >> power supplies with new capacitors. I fully expect that the >> replacements would last even longer than 20 years, however I rather >> doubt I'll be running those computers by then. > > Does anyone have much experience with the so-called "solid electrolyte" > electrolytics? Fvor replacing vintage caps, they're probably not a > viable choice as they're mostly SMT, but just wondering... I believe there are a few webpages out there written by people who have tried it. From what I remember reading about them years ago, they had no success when they tried to use them as replacements in switch mode power supplies (no surprise, since the solid polymer parts they attempted to use had way to low of ripple current rating for that application) but had better results with certain PC motherboards. I use solid polymers as replacements in some applications, and as they continue to decrease in cost, I've been considering using them more for replacement of aging SMD aluminum electrolytics. One application where I particularly like solid polymers is for replacement of the vcore regulator filter capacitors on Pentium 4 industrial single board computers (yes, the P4 is still /widely/ used and extremely common in that market, although it is slowly being replaced by the Core Duo). The original aluminum electrolytics in that application are usually 6.3V rated parts while the solid polymer replacements are 2.5V or 4V (vcore is under 2V). In addition to long term stability, another major benefit to solid polymers is that unlike aluminum electrolytics and solid tantalums, solid aluminum polymers they can be used at their full rated voltage with no ill effects. The only real downside that I know of for a solid polymer is that they have an incredibly low ESR (less than 0.01 ohm), which can actually upset older circuit designs which were not designed for capacitors with such a low ESR.
Re: PDP 11 gear finally moved
On Wed, 22 Jul 2015, Chuck Guzis wrote: On 07/22/2015 10:09 PM, Tothwolf wrote: One example I can give are some Pentium P55C architecture (Socket 7) systems which I've been running with minimal downtime for ~15 years. The original power supplies with their original (and relatively low quality) capacitors lasted about 15 to 17 years (I think the manufacture date code stamped on the oldest one was 1998) before the systems began to develop stability issues, requiring me to rebuild the power supplies with new capacitors. I fully expect that the replacements would last even longer than 20 years, however I rather doubt I'll be running those computers by then. Does anyone have much experience with the so-called "solid electrolyte" electrolytics? Fvor replacing vintage caps, they're probably not a viable choice as they're mostly SMT, but just wondering... I believe there are a few webpages out there written by people who have tried it. From what I remember reading about them years ago, they had no success when they tried to use them as replacements in switch mode power supplies (no surprise, since the solid polymer parts they attempted to use had way to low of ripple current rating for that application) but had better results with certain PC motherboards. I use solid polymers as replacements in some applications, and as they continue to decrease in cost, I've been considering using them more for replacement of aging SMD aluminum electrolytics. One application where I particularly like solid polymers is for replacement of the vcore regulator filter capacitors on Pentium 4 industrial single board computers (yes, the P4 is still /widely/ used and extremely common in that market, although it is slowly being replaced by the Core Duo). The original aluminum electrolytics in that application are usually 6.3V rated parts while the solid polymer replacements are 2.5V or 4V (vcore is under 2V). In addition to long term stability, another major benefit to solid polymers is that unlike aluminum electrolytics and solid tantalums, solid aluminum polymers they can be used at their full rated voltage with no ill effects. The only real downside that I know of for a solid polymer is that they have an incredibly low ESR (less than 0.01 ohm), which can actually upset older circuit designs which were not designed for capacitors with such a low ESR.
Re: PDP 11 gear finally moved
I wrote: >> I proposed it, and was willing to build microcontroller-based boards >> and write firmware, but IIRC it was decided that there was too little >> benefit. On Thu, Jul 23, 2015 at 12:00 PM, William Donzelli wrote: > That seems odd, considering the lengths you guys took on the caps, and > the whole museum mentality of keeping things "safe" for the artifacts. There's no artifact safety issue for the PDP-1 power supplies. They use a ferroresonant transformer, rectifiers, and filter capacitors. If any of those fail, the machine won't work properly, but it won't be damaged. If there had been voltage regulators, the failure of which could have resulted in serious overvoltage, we probably would have added crowbar circuits. In the Type 30 display, it's possible, though rather unlikely, for a failure in the deflection power supply to blow the deflection drive transistors. Adding a microcontroller isn't likely to avoid that. A crowbar circuit might be useful, though the damage happens so quickly that the deflection transistors might still fail.
RE: PDP 11 gear finally moved
> > * I once talked to a power supply guy about over-voltage sensors and > the like, and he said that over-voltage conditions (like a power > supply freaking out and giving TTL 8 Volts or something) due to > component failures are exceedingly rare. When it does happen, it is > almost always due to human error - mis-installing sense lines, > cranking a trimmer too far, setting line voltage improperly, and so > forth. This is presumably why all decent PSUs, even those without remote sensing, without twiddlepots to set the output voltage, etc, have crowbars. Manufacturers do not fit components for no good reason. I've had several instances where a PSU has 'gone crazy' in use. One time it was a dry joint on the sense resistor. Another was in a simple 3-terminal regualtor circuit where the common wire fell off the regulator [1]. The last which has happened several times, applies to common switch-mode designs, if the output smoothing capacitor goes high ESR (or in once case there was a bad VIA connecting it to the rest of the PSU -- and on an HP board at that) you get spike on the output of several times the desired output voltage. [1] 5A regulators are often in TO3 metal cans and the +ve one has the common connection to the case. If this is made by a solder tag under a fixing screw and said screw works loose then the output voltage can go sky-high. A neat trick if possible (i.e. when there is a separate input transsformer secondary/rectifier/smoothing cap for each regulator) is to put a tag under each fixing screw, input -ve to one, output -ve (system ground) to the other. Then if either screw comes loose you get no output as the circuit is opened. -tony -- Will
Re: PDP 11 gear finally moved
> I proposed it, and was willing to build microcontroller-based boards > and write firmware, but IIRC it was decided that there was too little > benefit. That seems odd, considering the lengths you guys took on the caps, and the whole museum mentality of keeping things "safe" for the artifacts. Microcontrollers and such probably are too complex - simple over-voltage* and over-current circuits to trip the EPO (or whatever DEC called it when the line was cut) would suffice, and give some of the more delicate components a fighting chance of survival. * I once talked to a power supply guy about over-voltage sensors and the like, and he said that over-voltage conditions (like a power supply freaking out and giving TTL 8 Volts or something) due to component failures are exceedingly rare. When it does happen, it is almost always due to human error - mis-installing sense lines, cranking a trimmer too far, setting line voltage improperly, and so forth. -- Will
Re: PDP 11 gear finally moved
On Thu, Jul 23, 2015 at 12:06 AM, William Donzelli wrote: > Did the team ever consider some sort of active monitoring of the > power, beyond whatever DEC implemented? I proposed it, and was willing to build microcontroller-based boards and write firmware, but IIRC it was decided that there was too little benefit.
Re: PDP 11 gear finally moved
> From: Lyle Bickley > we tested each capacitor for capacitance and ESR > ... > Each power supply had to meet it's specifications .. (every test was > logged and documented). > ... > Every year we do a complete DEC specified preventative maintenance on > the PDP-1 which includes testing every power supply for voltage, > stability and ripple. When you tested the caps, did you all write down all the results? (I see you logged the power supply results, so I'm guessing you all likely did for the caps too, but you didn't say explicitly.) You all haven't by any chance gone back and re-measured any of those caps, have you? (Again, standard PM likely doesn't include measuring individual components - although if you're not seeing any drift in the results, that's likely a sign that the components aren't 'evolving'.) If so, that would be really informative data about the longevity of these particular electrolytics. I say "these particular" because I'm starting to suspect that different electrolytics behave differently - likely because of fine details of internal construction, chemistry, etc. And it might even be details that the manufacturers were not aware of. I am reminded of a story (which I don't have time to chase down, to make sure I have the details right) from the SR-71, or maybe it was some NASA gear. Things all of a sudden started to fail in a way they had not before; after a great deal of investigation, it turned out something really minor had changed in the water supply to the manufacturing facility (perhaps they had started doing municipal fluoridation, I think). Noel
Re: PDP 11 gear finally moved
On 2015-07-23 07:09, Tothwolf wrote: On Tue, 21 Jul 2015, Lyle Bickley wrote: On Mon, 20 Jul 2015 23:14:36 -0600 Eric Smith wrote: On Mon, Jul 20, 2015 at 4:46 PM, Rich Alderson wrote: industry white papers with tables of decay rates for the aluminum electrolytics that indicate that, *no matter what*, they lose capacitance over time, until c. 14 years from manufacturer date they are at 10% of rating. That's very interesting. I haven't seen those white papers, but the "no matter what" must in fact depend on something, since on the PDP-1 Restoration Project we found that most of the 40 year old aluminum electrolytic capacitors still met their original specifications, including capacitance within rated tolerance. Of the few electrolytic capacitors that had failed, the problem was a catastrophic failure, not the capacitance being outside the rated tolerance. In the PDP-1, we preferred to keep the original components as much as possible. Had there been a capacitor, the failure which would have caused extensive damage to other components, we would have given serious consideration to replacing it. However, that was not the case for any of the capacitors in the PDP-1. Had our analysis indicated any expected benefit to replacing all of the electrolytic capacitors, we would have done so, and bagged and tagged the originals similar to what we did with failed components, so that they could be replaced if it ever was desired to return the artifact to its pre-restoration condition. I'm not recommending against LCM's policy, but I also wouldn't necessarily encourage anyone to adopt it, nor to adopt the practices of the CHM PDP-1 Restoration Project, without studying the issue. As Eric, I'm a member of the PDP-1 Restoration Team. The PDP-1 restoration was completed in 2005 - and annually we check the power supplies for voltage, ripple, etc. Not one of the re-formed capacitors have failed in the ten years since the completion of the restoration. I also re-formed all P/S capacitors in my PDP-8/S in September, 2013. Not one has failed since... How often is CHM's PDP-1 powered up and operated? If LCM's computers are going to be powered up and used routinely, it actually makes a lot of sense to go to the trouble to replace really old aluminum electrolytics, even if they seem to test good, since doing so is going to increase the reliability of frequently operated equipment. This is the reason why /I/ replace aluminum electrolytics when I'm making major repairs or fully reconditioning electronic equipment...I want said electronic widget to be as reliable as possible because it is never good when something breaks down while you are using it, especially with gear which needs to run 24/7/365 for years and years at a time. One example I can give are some Pentium P55C architecture (Socket 7) systems which I've been running with minimal downtime for ~15 years. The original power supplies with their original (and relatively low quality) capacitors lasted about 15 to 17 years (I think the manufacture date code stamped on the oldest one was 1998) before the systems began to develop stability issues, requiring me to rebuild the power supplies with new capacitors. I fully expect that the replacements would last even longer than 20 years, however I rather doubt I'll be running those computers by then. I've mostly tried to stay out of this thread, as I both am no expert on electronics, and also seems to have a very different view and experience than many around here. But I thought I should atleast give a datapoint for you all. I'm no museum type of person. I try to run my stuff all the time. And I normally do. And I do not replace things in running, working machines. And since I keep running the machines, they keep running on their original parts. And they just keep working. So I have various PDP-8 systems that have passed 40 years now, and they are still running fine. The same is true of my PDP-11 and VAX systems, that are now past 30 years. Running just fine. The biggest problems have always been with gear that have been sitting unused for a long time, and I don't think I have ever had to replace any large capacitors. A few small ones, yes. And lots of transistors in power supplies. Those are the thing most often causing problems in the +5V bricks in larger PDP-11s in my experience. But then again, I also have plenty of spares, so most of the time I have not bothered repairing them, and most spares sitting around have been fine, so the machines keep running. Biggest problems with PS for me was a couple of VAX 6400 machines, where the power supplies developed issues in running systems. The machines have been scrapped. Didn't like systems that develop problems like that. 8650 on the other hand is much better. But the external Unibus box currently have a power supply issue. But that machine (unfortunately had to sit a couple of years powered down, at which point it developed the problem). S
Re: PDP 11 gear finally moved
On Wed, 22 Jul 2015 09:01:35 -0400 (EDT) j...@mercury.lcs.mit.edu (Noel Chiappa) wrote: > > From: Tothwolf > > > How do you know those aluminum electrolytic capacitors are functioning > > just as good as they did when they were new? Unless you've tested them > > out of circuit ... > > ... aluminum electrolytic capacitors by their very electrochemical > > nature degrade as they age and as they are used. > > I am way out of my knowledge range in this discussion, but here's something I > wanted to ask about: how do you reconcile this observation (assertion?) with > the observations from several people (e.g. the PDP-1 people) that they _have_ > measured the electrolytics in their power supplies, and despite being N > decades old (where N ~= 5), they are _still_ within specs? If the very nature > of electrolytics mandates that they degrade, how are these still meeting > specs? > > I'm very confused... This is the last time I'm going to discuss this subject. IMHO, there's been way too much emotion expressed on what is a rather straightforward subject. The PDP-1 team is composed of seasoned engineers. Combined we have over 250 years of experience in high tech work and restoration. One Team member is a senior engineer at Tesla, two others are lead engineers in a different high tech medical startups/firms. Others of us are consultants to multiple Silicon Valley startups and companies. Almost all of us are serious vintage computer collectors. The PDP-1 at the CHM is demoed regularly for the public - and we run Spacewar! tournaments every quarter which are "sold out" (there is no fee - just signup). The PDP-1 is also regularly demoed regularly by some of us for friends and special guests of the Museum (or personal friends). Since the PDP-1 at the CHM is the only running PDP-1 in the world - and the fact that the Museum considers it a highly significant artifact - we made restoration decisions with those factors in mind. In accordance with standard Museum protocol, we tagged every bad part we removed from the PDP-1, bagged it and tagged it with the specific location it was removed from. We tagged all new (old stock) parts with a red dot. (In Museum protocol, one has to be able to restore an artifact to it's original condition - even if it is anticipated that will never occur). The CHM as other major Museums (like the Smithsonian) follow this protocol. We spent months laying out the restoration plan for the PDP-1 - and then spent about six months restoring all the power supplies. We made the easy decision to reform the capacitors in the PDP-1 as they were all computer grade - and had not visually leaked or "dried out". We used a very careful automated process to reform the capacitors which included a programmable power supply, current sensors and a laptop scripted to monitor the reformation progress. It was probably overkill - but we wanted to make sure we didn't overload any capacitor in the reformation process. After reforming every capacitor in every power supply, we tested each capacitor for capacitance and ESR. Only four of the reformed capacitors did not pass these tests. Two of us created an identical load test system that DEC had used to test the PDP-1 power supplies (multiple voltages, various currents, etc.). We then tested each power supply per DEC factory spec. starting at 85V and going as high as the spec. stated. Each power supply had to meet it's specifications in terms of voltage linearity and ripple (every test was logged and documented). IIRC, the above process took almost six months. (While we were working on power supplies, others were working on restoring fans (total strip down and restoration), checking every soldered connection, etc., etc. After we got the system up and passing all PDP-1 diagnostics - we went to work on the peripheral I/O gear - which took as long to restore as the PDP-1 CPU. The Model 30 display was particularly challenging. (We also reformed all the capacitors in the Model 30 display). Subsequently to the complete restoration, We ran regular demos on the PDP-1 - and during the first year we had a few minor bugs crop up - mostly memory and display related. The PDP-1 had been running demos for about 10 years and we've probably only had a handful of bogs over that period. We have NEVER had a P/S capacitor fail. Every year we do a complete DEC specified preventative maintenance on the PDP-1 which includes testing every power supply for voltage, stability and ripple. Of course we do many other tests as well - including running of all PDP-1 diagnostics. Almost every year the PDP-1 passes all tests flawlessly. -- Now to my own systems. For those of you who have checked my website, you'll see that I have a modestly large collection of systems. When I do restorations, I typically keep a logbook as we did on the CHM's PDP-1. I also reform all capacitors on my systems using a careful (but not as sophisti
Re: PDP 11 gear finally moved
On 7/23/2015 12:06 AM, William Donzelli wrote: As Eric, I'm a member of the PDP-1 Restoration Team. The PDP-1 restoration was completed in 2005 - and annually we check the power supplies for voltage, ripple, etc. Not one of the re-formed capacitors have failed in the ten years since the completion of the restoration. Did the team ever consider some sort of active monitoring of the power, beyond whatever DEC implemented? The big, chunky power supplies from the 1960s and 70s have the advantage that you can very often make completely reversible changes to the circuitry quite easily, due to all the screw terminals and the like - adding current and voltage sense points, crowbars, and other gizmos that just might save a transformer or two. And with today's technology, those gizmos could be very small and tucked away. I think that is their choice not ours. -- Will Ben.
Re: PDP 11 gear finally moved
> As Eric, I'm a member of the PDP-1 Restoration Team. The PDP-1 restoration > was completed in 2005 - and annually we check the power supplies for voltage, > ripple, etc. Not one of the re-formed capacitors have failed in the ten years > since the completion of the restoration. Did the team ever consider some sort of active monitoring of the power, beyond whatever DEC implemented? The big, chunky power supplies from the 1960s and 70s have the advantage that you can very often make completely reversible changes to the circuitry quite easily, due to all the screw terminals and the like - adding current and voltage sense points, crowbars, and other gizmos that just might save a transformer or two. And with today's technology, those gizmos could be very small and tucked away. -- Will
Re: PDP 11 gear finally moved
On 07/22/2015 10:09 PM, Tothwolf wrote: One example I can give are some Pentium P55C architecture (Socket 7) systems which I've been running with minimal downtime for ~15 years. The original power supplies with their original (and relatively low quality) capacitors lasted about 15 to 17 years (I think the manufacture date code stamped on the oldest one was 1998) before the systems began to develop stability issues, requiring me to rebuild the power supplies with new capacitors. I fully expect that the replacements would last even longer than 20 years, however I rather doubt I'll be running those computers by then. Does anyone have much experience with the so-called "solid electrolyte" electrolytics? Fvor replacing vintage caps, they're probably not a viable choice as they're mostly SMT, but just wondering... --Chuck
Re: PDP 11 gear finally moved
On Tue, 21 Jul 2015, Lyle Bickley wrote: On Mon, 20 Jul 2015 23:14:36 -0600 Eric Smith wrote: On Mon, Jul 20, 2015 at 4:46 PM, Rich Alderson wrote: industry white papers with tables of decay rates for the aluminum electrolytics that indicate that, *no matter what*, they lose capacitance over time, until c. 14 years from manufacturer date they are at 10% of rating. That's very interesting. I haven't seen those white papers, but the "no matter what" must in fact depend on something, since on the PDP-1 Restoration Project we found that most of the 40 year old aluminum electrolytic capacitors still met their original specifications, including capacitance within rated tolerance. Of the few electrolytic capacitors that had failed, the problem was a catastrophic failure, not the capacitance being outside the rated tolerance. In the PDP-1, we preferred to keep the original components as much as possible. Had there been a capacitor, the failure which would have caused extensive damage to other components, we would have given serious consideration to replacing it. However, that was not the case for any of the capacitors in the PDP-1. Had our analysis indicated any expected benefit to replacing all of the electrolytic capacitors, we would have done so, and bagged and tagged the originals similar to what we did with failed components, so that they could be replaced if it ever was desired to return the artifact to its pre-restoration condition. I'm not recommending against LCM's policy, but I also wouldn't necessarily encourage anyone to adopt it, nor to adopt the practices of the CHM PDP-1 Restoration Project, without studying the issue. As Eric, I'm a member of the PDP-1 Restoration Team. The PDP-1 restoration was completed in 2005 - and annually we check the power supplies for voltage, ripple, etc. Not one of the re-formed capacitors have failed in the ten years since the completion of the restoration. I also re-formed all P/S capacitors in my PDP-8/S in September, 2013. Not one has failed since... How often is CHM's PDP-1 powered up and operated? If LCM's computers are going to be powered up and used routinely, it actually makes a lot of sense to go to the trouble to replace really old aluminum electrolytics, even if they seem to test good, since doing so is going to increase the reliability of frequently operated equipment. This is the reason why /I/ replace aluminum electrolytics when I'm making major repairs or fully reconditioning electronic equipment...I want said electronic widget to be as reliable as possible because it is never good when something breaks down while you are using it, especially with gear which needs to run 24/7/365 for years and years at a time. One example I can give are some Pentium P55C architecture (Socket 7) systems which I've been running with minimal downtime for ~15 years. The original power supplies with their original (and relatively low quality) capacitors lasted about 15 to 17 years (I think the manufacture date code stamped on the oldest one was 1998) before the systems began to develop stability issues, requiring me to rebuild the power supplies with new capacitors. I fully expect that the replacements would last even longer than 20 years, however I rather doubt I'll be running those computers by then.
Re: PDP 11 gear finally moved
On Wed, Jul 22, 2015 at 9:33 AM, Tothwolf wrote: > The only > thing we could know today is if the capacitor passes industry standard tests > and if the power supply those capacitors are a part of functions correctly > when fully loaded. We built a dummy load for testing the DEC Type 728 power supplies under four different load conditions (combinations of loads on the two outputs), and verified that the ripple was within DEC specifications. The power supplies are retested for voltage and ripple every year. If the ESR increased very much, it would result in a noticable increase in ripple. Here's an example of the test results which are kept on file: http://www.computerhistory.org/collections/catalog/102663945 The majority of the DC supplies in the PDP-1 are Type 728, but there are a few other types as well, and they were and are tested also.
Re: PDP 11 gear finally moved
Tail and signaling lights put much more stress on the filament. The headlights are burned steady in practice and will burn out when they burn out. I never replace both, and seldom see any correlation. I just put the spare in the trunk with the kit to get at the lights when they do fail. I figure selling them in pairs makes sense to the marketers since they have seen demand replace both. But I don't mind having them burn out before replacement. Safety would dictate never having to operate the vehicle with failed signals, so it can be justified, I suppose to replace both to minimize that, but there is no way to justify regular replacement of bulbs just because they may fail. To the original discussion, if disassembling and accessing the bulbs is a pain in the ass, as it is for most systems, making sure all lamps are in good condition when the panel is uninstalled (which puts stress on the connectors, fasteners) by checking and replacing any which don't appear to be in good condition makes sense. Jim On 7/22/2015 8:00 AM, Al Kossow wrote: On 7/22/15 7:43 AM, Tothwolf wrote: I can't say I've previously heard of that being done with automotive bulbs Then why are tail light bulbs sold in pairs? I just had one go, and replaced both sides.
Re: PDP 11 gear finally moved
On 07/22/2015 04:39 AM, tony duell wrote: Do you seriously replace both headlight bulbs when one fails? I know of nobody who does that. Generally you carry a spare bulb kit and a screwdriver and if a bulb fails, pull over and change it. Why not change all other bulbs on the car at the same time? Or change them all once a year as part of the service [1]? What about bulbs in your house? Automotive bulbs (at least those used for external illumination and indication are used in pairs. Most incandescent bulbs fail with age (manufacturing defects are an exception) and their light output decreases--the filament evaporates and darkens the envelope. It's logical to anticipate that if an old lamp fails, its partner is not going to be long in following it. The effort to replace two bulbs is not much different than the effort involved in replacing one. In my home, if an old fluorescent tube in a multi-lamp fixture darkens and fails, I replace all lamps in the fixture. This also applies to multi-bulb incandescent fixtures. Again, balanced with the bother of hauling out a ladder and, in some cases, disassembling the fixture, it just makes sense. Maybe I'm the only one who does this (and perhaps I'm the only one who coats incandescent lamp bases with a thin layer of dielectric grease), but it works for me. Non-solid electrolytic capacitors do have a rated service life and so merit replacement after a certain age (depending on service conditions). --Chuck
RE: PDP 11 gear finally moved
On Wed, 22 Jul 2015, tony duell wrote: On Wed, 22 Jul 2015, Noel Chiappa wrote: I am way out of my knowledge range in this discussion, but here's something I wanted to ask about: how do you reconcile this observation (assertion?) with the observations from several people (e.g. the PDP-1 people) that they _have_ measured the electrolytics in their power supplies, and despite being N decades old (where N ~= 5), they are _still_ within specs? If the very nature of electrolytics mandates that they degrade, how are these still meeting specs? Well, at least 2 possibilities... Firstly, the tolerance of the capacitance of an electrolytic capacitor is very wide -- -20% to +80% is not uncommon. So it's quite possible they started off at the top end of that range, have deteriorated over the years, and are still within spec. Of course nobody can prove that (unless there are records of the values meaured 50 years ago) and nobody really knows how they will continue to change (if indeed they do). Secondly, I have no idea what was measured. The capacitance value is not the whole story by any means. In fact the most important thing most of the time is ESR (Effective Series Resistance) which increases as the electrolyte dries up. The ESR of these components could well still be OK after 50 years, but again nobody knows what it was when they were new. That said, I keep on with the comment that the important thing is 'does the circuit behave as required', If so, then the capacitor is almost by definition OK in that circuit. From what I remember from an earlier discussion about that PDP-1, after reforming, those large capacitors were leak tested at or slightly above their rated voltage. As for meeting spec, unless DEC documented what their original design criteria was, there really is no way to know with 100% certainty. The only thing we could know today is if the capacitor passes industry standard tests and if the power supply those capacitors are a part of functions correctly when fully loaded.
Re: PDP 11 gear finally moved
> From: tony duell > it's quite possible they started off at the top end of that range, have > deteriorated over the years, and are still within spec. Of course > nobody can prove that (unless there are records of the values meaured > 50 years ago) Well, I don't know about 50 years, but I know some of the restorations (where people said they checked that their electrolytics were still withina spec) were a while back, so _iff_ they have records of what they measured, it would be interesting to see if there's any drift from then, to now. But I have no idea what numbers they have, they'd have to speak to that. > I have no idea what was measured. The capacitance value is not the > whole story by any means. In fact the most important thing most of the > time is ESR Again, I have no idea what they measured, so they'd have to respond on that. Noel
RE: PDP 11 gear finally moved
On Wed, 22 Jul 2015, tony duell wrote: I think he did answer it. If the unit is operating correctly then the capacitors must be sufficiently good at that time for that unit. Now, whether they will go on working is something that is very hard to tell. But that applies to every other component in the unit. An IC might work find now and suffer bond-out wire failure later on the same day. Going purely from the historical data, failures of most semiconductors are /far/ less frequent than an aluminum electrolytic capacitor (except for a handful of certain TTL logic, which has been discussed previously here on classiccmp and elsewhere). Just like the NiCd and SLA batteries I mentioned, aluminum electrolytic capacitors by their very electrochemical nature degrade as they age and as they are used. You cannot claim that a 20-30 year aluminum electrolytic Semiconductors also degrade both with time and use. I would think a 30-year-old 3 terminal regulator IC was also beyond its design life. So do you replace those 'anyway'? The damage done if one those fails is likely to greatly exceed the damage done if a capacitor fails. Honestly, I've not seen all that many failed 3-terminal voltage regulators in the field. I've seen some which failed due to insufficient cooling or a loose heatsink, or with a hole blown in them after being hit with 24V AC, but not any that have failed short under normal use. Do you replace all EPROMs in case they develop bit-rot (They are most likely way beyond their design life by now)? I think like most of us on this list, anything I have which is mission critical gets backed up and can easily be reprogrammed if it fails. Most of the problems I've seen with bit-rot of EPROMs have been cases where their quartz windows were not originally covered. I use opaque foil stickers (I can see if I can find the part number for the stickers I use if anyone needs it) on any UV erasable memories I program and I haven't had issues with corrupt data.
RE: PDP 11 gear finally moved
> > Date: Mon, 20 Jul 2015 14:11:46 + > From: tony duell > Subject: RE: PDP 11 gear finally moved > > > > Replace - yes, *especially* if you don't have a big budget. Aluminum > > electrolytic capacitors are CHEAP and easy to obtain. Replacement > > semiconductors by comparison are expensive and can be quite difficult to > > find. > The RICM ignored the sage advice from experts and reformed the electrolytics in the PDP-12 that we are currently working on. This decision was based on our past experience on other restorations, the lack of replacements in the same physical size, and the very high cost of the replacements. So far the system is behaving nicely. We have had several spectacular failures of the AC caps with the ferroresonant circuit in DEC power supplies. We regularly replace the AC caps because they are available and inexpensive. -- Michael Thompson
RE: PDP 11 gear finally moved
On Wed, 22 Jul 2015, tony duell wrote: Given that a typical aluminum electrolytic capacitor costs anywhere from $0.12-$0.15 (4mm or 5mm diameter radials) to about $1.00 (12mm or 16mm diameter radial), it also doesn't make much sense to desolder a 20 year old part, spend at a minimum 5 or more minutes testing it, and then solder it back in. It it much more economical to pull the old part and install a new one and be done with it. (You also don't have to worry if the desoldering and resoldering process might have damaged the original parts end-seals.) That said, I personally pre-test new parts, in bulk, before I I don't remove parts unless they have something to do with the problem I am solving. If the power rails are the right voltage with sufficiently low ripple then I look elsewhere for probkems. put them into my stock, so I know ahead of time that I'm installing known-good parts. You claim that electrolytics deteriorate with time whether used or not. How do you know the ones you install haven't deteriorated since you tested them? When I pull capacitors from a board, I put them into numbered trays for testing. Each new part also gets another quick test before installation and the results of both get entered into a spreadsheet (along with date codes, part numbers, and any other data I have on hand). I did this initially for mission critical boards so I could provide the data to customers who needed that level of detail, but I later started doing this for all repairs because I found it wasn't all that difficult to do once I already had a system in place. When I'm testing old parts, I also note things like leaky seals, corrosion around the terminals, etc. Because of the historical data I've collected, I can also tell from my notes that there are definitely certain brand/series (both vintage and modern) which have common issues.
Re: PDP 11 gear finally moved
On 7/22/15 7:43 AM, Tothwolf wrote: I can't say I've previously heard of that being done with automotive bulbs Then why are tail light bulbs sold in pairs? I just had one go, and replaced both sides.
RE: PDP 11 gear finally moved
On Wed, 22 Jul 2015, tony duell wrote: On Wed, 22 Jul 2015, ANDY HOLT wrote: Do you seriously replace both headlight bulbs when one fails? I know of nobody who does that. Generally you carry a spare bulb kit and a screwdriver and if a bulb fails, pull over and change it. and - like the capacitor replacement question this is an "it depends". For some cars - including the Mercedes A-class (at least earlier models) - it is almost impossible to change the headlight bulb when the car is at ground level because it is accessed through a hatch in the wheel arch, whereas if the car ARGH!!! But presumably you carry a jack and tools to change a wheel. Can you not just remove the wheel on the correct side to reach the hatch (not that I want to work on a car not supported on proper axle stands...) Having had a number of bulbs that failed shortly (but not very shortly) after installation (nothing to do with headlamps, and not quartz-halogen bulbs so it was not contamination of the envelope that was the problem) I wonder if necessarily changing a good bulb is a good idea... I can't say I've previously heard of that being done with automotive bulbs, but I do know that some pinball guys who do this. After a couple of lamps go out, they will replace them all at the same time because it usually isn't easy to change them, and once the lamps reach a certain number of power on hours, they start failing more and more frequently.
RE: PDP 11 gear finally moved
> > Do you seriously replace both headlight bulbs when one fails? I know of > > nobody who does that. Generally you carry a spare bulb kit and a screwdriver > > and if a bulb fails, pull over and change it. > and - like the capacitor replacement question this is an "it depends". > For some cars - including the Mercedes A-class (at least earlier models) - it > is > almost impossible to change the headlight bulb when the car is at ground level > because it is accessed through a hatch in the wheel arch, whereas if the car ARGH!!! But presumably you carry a jack and tools to change a wheel. Can you not just remove the wheel on the correct side to reach the hatch (not that I want to work on a car not supported on proper axle stands...) Having had a number of bulbs that failed shortly (but not very shortly) after installation (nothing to do with headlamps, and not quartz-halogen bulbs so it was not contamination of the envelope that was the problem) I wonder if necessarily changing a good bulb is a good idea... > is up on the garage lift with the wheel removed it is trivial. In that case > it is > probably best to change both bulbs when one fails. Why not just change them both as part of the 12000 mile service (or whatever)? I am sure I once heard of a regulation that car bulbs (at least the legally required ones) had to be changeable at the roadside with a minimum of tools. Looks like that is universally ignored -tony
RE: PDP 11 gear finally moved
> >> From: Tothwolf > >> How do you know those aluminum electrolytic capacitors are functioning >> just as good as they did when they were new? Unless you've tested them >> out of circuit ... > > ... aluminum electrolytic capacitors by their very electrochemical > > nature degrade as they age and as they are used. > > I am way out of my knowledge range in this discussion, but here's something I > wanted to ask about: how do you reconcile this observation (assertion?) with > the observations from several people (e.g. the PDP-1 people) that they _have_ > measured the electrolytics in their power supplies, and despite being N > decades old (where N ~= 5), they are _still_ within specs? If the very nature > of electrolytics mandates that they degrade, how are these still meeting > specs? Well, at least 2 possibilities... Firstly, the tolerance of the capacitance of an electrolytic capacitor is very wide -- -20% to +80% is not uncommon. So it's quite possible they started off at the top end of that range, have deteriorated over the years, and are still within spec. Of course nobody can prove that (unless there are records of the values meaured 50 years ago) and nobody really knows how they will continue to change (if indeed they do). Secondly, I have no idea what was measured. The capacitance value is not the whole story by any means. In fact the most important thing most of the time is ESR (Effective Series Resistance) which increases as the electrolyte dries up. The ESR of these components could well still be OK after 50 years, but again nobody knows what it was when they were new. That said, I keep on with the comment that the important thing is 'does the circuit behave as required', If so, then the capacitor is almost by definition OK in that circuit. -tony I'm very confused... Noel
Re: PDP 11 gear finally moved
really good caps are "better than specs" and thus deteriorate "into specs" over time, but all fade eventually. Some may have connectors that die before the cap inside. Rarely does a cap actually measure the same exactly as what is printed on the label. The ESR value vs. the capacity is the factor, and you can really get into "is this a good cap?" world depending on what equipment you're using. Personally I have learned a lot about the subject in the past 5 years, you learn some caps are more important than others, and how "in spec" they are can be less important depending on the job being done. On Wed, Jul 22, 2015 at 9:01 AM, Noel Chiappa wrote: > > From: Tothwolf > > > How do you know those aluminum electrolytic capacitors are functioning > > just as good as they did when they were new? Unless you've tested them > > out of circuit ... > > ... aluminum electrolytic capacitors by their very electrochemical > > nature degrade as they age and as they are used. > > I am way out of my knowledge range in this discussion, but here's something I > wanted to ask about: how do you reconcile this observation (assertion?) with > the observations from several people (e.g. the PDP-1 people) that they _have_ > measured the electrolytics in their power supplies, and despite being N > decades old (where N ~= 5), they are _still_ within specs? If the very nature > of electrolytics mandates that they degrade, how are these still meeting > specs? > > I'm very confused... > > Noel -- Bill vintagecomputer.net
Re: PDP 11 gear finally moved
> From: Tothwolf > How do you know those aluminum electrolytic capacitors are functioning > just as good as they did when they were new? Unless you've tested them > out of circuit ... > ... aluminum electrolytic capacitors by their very electrochemical > nature degrade as they age and as they are used. I am way out of my knowledge range in this discussion, but here's something I wanted to ask about: how do you reconcile this observation (assertion?) with the observations from several people (e.g. the PDP-1 people) that they _have_ measured the electrolytics in their power supplies, and despite being N decades old (where N ~= 5), they are _still_ within specs? If the very nature of electrolytics mandates that they degrade, how are these still meeting specs? I'm very confused... Noel
Re: PDP 11 gear finally moved
This thread has gone on for a while and I think we all get the points here, but one other consideration - how will removing and replacing a component damage the board? Damage the board and it's game over. One should always take the overall board's ability to handle replacement. With the board in mind, I avoid any part replacements and try to keep them to what is proven necessary only. On Wed, Jul 22, 2015 at 8:18 AM, tony duell wrote: > >> > They reliably do what they're supposed to do. >> >> You didn't answer the question. How do you know those aluminum >> electrolytic capacitors are functioning just as good as they did when they >> were new? Unless you've tested them out of circuit, you simply cannot make > > That, actually, is the wrong question to ask. You should ask 'How do you > know if these old capacitors are working as well as the brand-new replacements > will'. > >> that assertion. > > I think he did answer it. If the unit is operating correctly then the > capacitors must be > sufficiently good at that time for that unit. > > Now, whether they will go on working is something that is very hard to tell. > But that applies > to every other component in the unit. An IC might work find now and suffer > bond-out wire > failure later on the same day. > >> Just like the NiCd and SLA batteries I mentioned, aluminum electrolytic >> capacitors by their very electrochemical nature degrade as they age and as >> they are used. You cannot claim that a 20-30 year aluminum electrolytic > > Semiconductors also degrade both with time and use. I would think a > 30-year-old > 3 terminal regulator IC was also beyond its design life. So do you replace > those > 'anyway'? The damage done if one those fails is likely to greatly exceed the > damage > done if a capacitor fails. > > Do you replace all EPROMs in case they develop bit-rot (They are most likely > way > beyond their design life by now)? > > -tony -- Bill vintagecomputer.net
Re: PDP 11 gear finally moved
>>>> From: "tony duell" To: "General Discussion: On-Topic and Off-Topic Posts" Sent: Wednesday, 22 July, 2015 12:39:42 PM Subject: RE: PDP 11 gear finally moved > > I might think twice about doing a board that was fragile with age, but > otherwise, change 'em all. Like replacing both headlight bulbs if one > goes out--it's just a matter of time before the other one goes. Do you seriously replace both headlight bulbs when one fails? I know of nobody who does that. Generally you carry a spare bulb kit and a screwdriver and if a bulb fails, pull over and change it. <<<< and - like the capacitor replacement question this is an "it depends". For some cars - including the Mercedes A-class (at least earlier models) - it is almost impossible to change the headlight bulb when the car is at ground level because it is accessed through a hatch in the wheel arch, whereas if the car is up on the garage lift with the wheel removed it is trivial. In that case it is probably best to change both bulbs when one fails. For capacitors (to get back OT) I'd be inclined to take one failure as "happenstance" whereas a second one as beginning to show a pattern. Andy
RE: PDP 11 gear finally moved
> > They reliably do what they're supposed to do. > > You didn't answer the question. How do you know those aluminum > electrolytic capacitors are functioning just as good as they did when they > were new? Unless you've tested them out of circuit, you simply cannot make That, actually, is the wrong question to ask. You should ask 'How do you know if these old capacitors are working as well as the brand-new replacements will'. > that assertion. I think he did answer it. If the unit is operating correctly then the capacitors must be sufficiently good at that time for that unit. Now, whether they will go on working is something that is very hard to tell. But that applies to every other component in the unit. An IC might work find now and suffer bond-out wire failure later on the same day. > Just like the NiCd and SLA batteries I mentioned, aluminum electrolytic > capacitors by their very electrochemical nature degrade as they age and as > they are used. You cannot claim that a 20-30 year aluminum electrolytic Semiconductors also degrade both with time and use. I would think a 30-year-old 3 terminal regulator IC was also beyond its design life. So do you replace those 'anyway'? The damage done if one those fails is likely to greatly exceed the damage done if a capacitor fails. Do you replace all EPROMs in case they develop bit-rot (They are most likely way beyond their design life by now)? -tony
RE: PDP 11 gear finally moved
> > I might think twice about doing a board that was fragile with age, but > otherwise, change 'em all. Like replacing both headlight bulbs if one > goes out--it's just a matter of time before the other one goes. Do you seriously replace both headlight bulbs when one fails? I know of nobody who does that. Generally you carry a spare bulb kit and a screwdriver and if a bulb fails, pull over and change it. Why not change all other bulbs on the car at the same time? Or change them all once a year as part of the service [1]? What about bulbs in your house? [1] OK, this is done for things like lighthouse bulbs which are replaced after so many hours of operation, but that is a rather different case. -tony
RE: PDP 11 gear finally moved
> > that are running perfectly "just in case"... > > How do you -know- they are "running perfectly"? Just because a widget > itself is functioning, you have no way of knowing if that capacitor is > working 100% properly /unless/ you actually remove it from circuit and run > a full battery of tests on it. Simply measuring the capacitance with a DMM > while a capacitor is in circuit isn't good enough. I am reminded of something that was written either in the manual for my 'scope or in Tekscope (I forget which). Namely that 'The best tube tester is the circuit that uses the tube'. Tektronix deprecated the use of tube/valve testers for finding faults in their instruments It applies to capacitors too. If the _circuit_ (power supply or whatever) works correcty the the capacitor is good enough for that circuit. Whether or not it meets some published specs or not. > Given that a typical aluminum electrolytic capacitor costs anywhere from > $0.12-$0.15 (4mm or 5mm diameter radials) to about $1.00 (12mm or 16mm > diameter radial), it also doesn't make much sense to desolder a 20 year > old part, spend at a minimum 5 or more minutes testing it, and then solder > it back in. It it much more economical to pull the old part and install a > new one and be done with it. (You also don't have to worry if the > desoldering and resoldering process might have damaged the original parts > end-seals.) That said, I personally pre-test new parts, in bulk, before I I don't remove parts unless they have something to do with the problem I am solving. If the power rails are the right voltage with sufficiently low ripple then I look elsewhere for probkems. > put them into my stock, so I know ahead of time that I'm installing > known-good parts. You claim that electrolytics deteriorate with time whether used or not. How do you know the ones you install haven't deteriorated since you tested them? > On many occasions I've cut open old aluminum electrolytics, and the guts > very much do deteriorate with age. In addition to corrosion of the foil > (black spots and pitting) and foil to terminal junctions (corrosion), one > thing I particularly noticed was the more operating hours an aluminum > electrolytic capacitor had on it, the more its electrolyte and paper > insulator tended to smell bad compared to an otherwise identical (same > brand and series) part that had very low hours. These are all clear signs > of deterioration. Firstly the paper is not the insulator. After all, it is soaked in electrolyte. And 'smell bad'??? OK, so some chemical change has taken place, but how do you know it is detrimental to the performance of the capacitor? -tony
Re: PDP 11 gear finally moved
On Tue, 21 Jul 2015, Mike Stein wrote: On Tue, 21 Jul 2015, Tothwolf wrote: On Tue, 21 Jul 2015, Mike Stein wrote: FWIW I'm certainly not about to spend 100s of dollars, not to mention time spent in sourcing and replacing, to replace the caps in systems 100s? Where are you sourcing your components from? The typical board I rebuild has a component cost of about $20 or less. Smaller switchmode PSUs with a bunch of 10-18mm radials might be closer to $35-50. Larger PSUs /might/ cost closer to $100 if they have several large screw terminal capacitors in them. All things considered, that isn't very much money in today's dollars, and considering the full replacement cost of some of these boards (if they are even available), those preventive maintenance costs are an absolute bargain, /especially/ if you are doing the work yourself on your own time. Maybe it isn't much money in your world, especially when someone else is paying. Like anyone else, I have to buy the parts I use for my own equipment. If someone else wants to volunteer to buy them for me, I'm certainly not going to argue though ;) I just priced the main power supply caps in one of my Cromemco systems and it comes to ~ $120 (and all special order of course); if I replaced all the caps in all my (working) systems as you and a few others are suggesting across the board regardless of the system, condition etc., it would easily exceed $2000 if I could even find suitable replacements. Without an actual list of components required and without knowing which vendors you are getting your price quotes from, I have no way to verify if your $120 total is representative of the norm. If your Cromemco system is still functioning to your satisfaction, and you have zero interest in replacing aluminum electrolytic capacitors as part of preventative maintenance, why are you even bothering to price them? I also seem to remember saying earlier in the thread: "In the odd case where a computer grade screw terminal capacitor is extremely expensive or completely unobtainable (those which I've purchased were under $20-30) I might be willing to leave an original part in place, *if* it can pass a leakage test." And what about those prone to explode tantalums while we're at it... Well, if you want to bring those up and expand on the list of "bad caps" I mentioned, early SMD solid tantalums seem to be quite problematic in terms of spontaneously shorting out and going up in flames, even when operated at half their rated voltage (as specified by the capacitor manufacturers). I can't say I've seen a higher failure rate with newer SMD tantalums than say modern SMD multilayer ceramics, however after having to scrape the remains of many charred SMD tantalums off of (unobtainium) boards undergoing repair, I can't say I really trust them. YMMV. If you're recapping 20-year old or newer circuit boards for customers as you apparently are then it does indeed often make sense to replace all the aluminum electrolytics, especially if the board has problems or there's visual evidence of failure, but let those of us with older, well-working systems use our _judgement_ whether to replace or not. OK? To each his own... I've previously done a great deal of commercial work (not now though), however I still do the very same work on my own equipment. I currently have somewhere north of 300 projects in my to-do queue (everything from modern stuff made a few years ago to test equipment and radios from the 1950s and earlier) which I've already purchased and kitted up parts for (of which I'd say about 2/3 are aluminum electrolytic capacitors). I know /exactly/ what *I* spent on my parts (I have it all organized in spreadsheets, just like I did for commercial projects), and my own parts costs do not at all seem to match up with what you are describing. I can also state from experience that the majority of capacitor failures (wear out; change in capacitance and increasing electrical leakage at working voltage) do not exhibit visual signs of failure or impending failure. The main exception are some of those really low quality far-east parts made in the last decade or so which manufactures use in consumer grade electronics. that are running perfectly "just in case"... How do you -know- they are "running perfectly"? [Just because a widget itself is functioning, you have no way of knowing if that capacitor is working 100% properly /unless/ you actually remove it from circuit and run a full battery of tests on it. Simply measuring the capacitance with a DMM while a capacitor is in circuit isn't good enough.] They reliably do what they're supposed to do. You didn't answer the question. How do you know those aluminum electrolytic capacitors are functioning just as good as they did when they were new? Unless you've tested them out of circuit, you simply cannot make that assertion. Just like the NiCd and SLA batteries I ment
Re: PDP 11 gear finally moved
- Original Message - From: "Tothwolf" To: "General Discussion: On-Topic and Off-Topic Posts" Sent: Tuesday, July 21, 2015 9:46 PM Subject: Re: PDP 11 gear finally moved On Tue, 21 Jul 2015, Mike Stein wrote: ... FWIW I'm certainly not about to spend 100s of dollars, not to mention time spent in sourcing and replacing, to replace the caps in systems 100s? Where are you sourcing your components from? The typical board I rebuild has a component cost of about $20 or less. Smaller switchmode PSUs with a bunch of 10-18mm radials might be closer to $35-50. Larger PSUs /might/ cost closer to $100 if they have several large screw terminal capacitors in them. All things considered, that isn't very much money in today's dollars, and considering the full replacement cost of some of these boards (if they are even available), those preventive maintenance costs are an absolute bargain, /especially/ if you are doing the work yourself on your own time. Maybe it isn't much money in your world, especially when someone else is paying. I just priced the main power supply caps in one of my Cromemco systems and it comes to ~ $120 (and all special order of course); if I replaced all the caps in all my (working) systems as you and a few others are suggesting across the board regardless of the system, condition etc., it would easily exceed $2000 if I could even find suitable replacements. And what about those prone to explode tantalums while we're at it... If you're recapping 20-year old or newer circuit boards for customers as you apparently are then it does indeed often make sense to replace all the aluminum electrolytics, especially if the board has problems or there's visual evidence of failure, but let those of us with older, well-working systems use our _judgement_ whether to replace or not. OK? To each his own... that are running perfectly "just in case"... How do you -know- they are "running perfectly"? They reliably do what they're supposed to do. m
RE: PDP 11 gear finally moved
On Tue, 21 Jul 2015, tony duell wrote: On Mon, 20 Jul 2015, Tothwolf wrote: Yes, the grid cap would /usually/ be a non-polarized wax paper type, which tend to be very unreliable. I've yet to find a wax paper type which will pass a leak test and those are also on my replace on sight list. Of course you wouldn't want to replace mica, ceramic, or plastic film parts without good reason, but if a set is going to be more than just a shelf queen, aluminum electrolytics and wax paper capacitors are a It depends a lot on the circuit. If replacing the capacitor is going to involve major realignment and the original is probably OK and leakage is not going to do further damage (likely in the case of a tuning component) then I will leave it and only replace if it fails. IMO an alignment is simply part of the restoration process. When I service a set, I do so expecting that it is going to be used and thus needs to have an accurate dial vs just sitting on a shelf. Simply installing replacement aluminum electrolytics and wax-paper capacitors is not likely to affect alignment. It is extremely common however to find sets where someone else has previously mucked up the original alignment in an attempt to work around electrically leaky wax-paper capacitors which have caused the band the drift. must-replace item. Carbon film resistors in this sort of equipment should also be tested, however I only replace those which are either bad or out of tolerance (some brands held up better than others). This is inconistent. A capacitor which is failing (starting to leak, say) may get worse. A resistor which is drifting may get worse. Either can do more damage when it fails. Why replace the cap and not the resistor? Why is that inconsistent? If I test a carbon comp resistor and it measures within spec, there isn't much reason to replace it. Unlike an aluminum electrolytic capacitor, a carbon comp resistor is very stable chemically. Carbon comp resistors tend to drift due to absorption of moisture, and while it is possible to dry one out in a toaster oven at a controlled temperature, the resistor will again drift out again over time, so if one is out of spec, replacement is the best option. I probably would replace certain safety-related capacitors in live chassis sets, like ones that isolate external sockets, using class Y replacements. But that;s about it. That's a good idea, however something to keep in mind is that class Y safety rated capacitors are not designed not to short (and not put say a I thought that was the difference between class X (will fail in a safe way, but may short) and class Y (will not short). The latter are to be used where 'failure of the capacitor may expose a person to electric shock' according to the data sheets I've read. In general class X go across the mains, class Y from mains to ground. Except that the chassis in modern equipment is /expected/ to be connected to ground, unlike a floating or hot chassis in a vintage radio. Both class X and class Y can fail short. A class Y tends to have a thicker dielectric and/or a lower voltage rating, which means it is less likely to fail short, not that is cannot fail short. I consider replacing aluminum electrolytics to be preventive maintenance. One wouldn't drive a 20-50 year old car with original hoses, belts, and tires, and IMO it is just common sense to replace electronic components such as aluminum electrolytic capacitors which have extremely well documented life expectancies and failure rates. I do wonder if this data is based on the cheaper components used in consumer electronics (paticularly things like AA5s) and that the capacitors used in computers were of a much higher quality and longer life. Possibly. Radio repair shops of the AA5 era also had a vested interest in turning a set around as quickly (and as cheaply) as possible, and a set back in again in the same year for another repair was also good for their business. Back then, consumers expected their radios to need "routine" service, so people were less likely to even question it. I've come to this conclusion based on the types and quality of radio shop repairs I've seen in these old sets. I have a radio in my to-do queue right now (an AA5) which was owned by my grandparents, where a shop needlessly hacked the leads off a Centralab hybrid module and replaced about half of its functionality with some really cheap wax-paper capacitors and a handful of resistors (after searching for a number of years, I actually managed to find a NOS module for it, so that part of the circuit will be restored to its original condition when I eventually get to that project). As far as shotgun-repairs go, one of my own pet peeves are those out there selling "cap kits" (usually really low quality [sometimes counterfeit] Oh don't get me started Cap kits or counterfeits? ;) Best way to avoid counterfeits...do not buy modern name b
Re: PDP 11 gear finally moved
On 07/21/2015 06:56 PM, Tothwolf wrote: I've often wondered why they even bother to put that polarity stripe on modern film parts when it doesn't actually indicate the outside foil terminal. Maybe this is something that has become lost knowledge to manufacturers over the years to the point where even Vishay/Sprague doesn't know what that black indicator stripe was actually used for? And not so modern parts. I've still got a few pounds of paper-oil capacitors (lots of Rifas) from the 1980s. Picked them up as mixed NOS priced about 25 cents per pound. About half are market with polarity marks. I never understood why. I used one recently to replace an ignition capacitor in a 40 year old chainsaw (a Stihl 056). Works a treat. --Chuck
Re: PDP 11 gear finally moved
On 07/21/2015 06:46 PM, Tothwolf wrote: I dunno about that. When I've done commercial boards such as industrial process controllers and CPUs for customers with nearly unlimited funds, I charged the customer based on an hourly rate. Since I use a vacuum desoldering tool, changing out 10-15 aluminum electrolytics on a board took me not much more time than 1-2. Most of the time spent on a board that comes out of the field is spent on cleaning, testing (before and after repairs) and prep, and it only takes a few seconds to pull the solder off of a couple of component leads. Replacing aged electrolytics wholesale on these types of boards also meant I didn't need to worry that the same board would be back on my bench again in the next 3-6 months. These days, I'm not taking on any new commercial work though, there was just too much demand due to all those shoddy far-east made capacitors, and it meant I pushed aside all my own projects. Commercial/industrial boards are a whole different matter and I agree with you there. The quality of the service performed is of more importance, often that the cost. Consider a floppy controller board for a name-brand PLC. You can get one for about $5000--not the PLC, but the floppy board. The customer expects the PLC to last the life of the tool it's controlling--30 years is not atypical. I've often thought that if some of the scrappers out there could recognize some of the stuff they ground up for precious metals, they'd think twice. I might think twice about doing a board that was fragile with age, but otherwise, change 'em all. Like replacing both headlight bulbs if one goes out--it's just a matter of time before the other one goes. --Chuck
Re: PDP 11 gear finally moved
On Mon, 20 Jul 2015, Mark J. Blair wrote: On Jul 20, 2015, at 18:02 , Tothwolf wrote: I replace wax paper types with polyester (mylar), polystyrene or ceramic discs, depending on how they are used in the circuit (note however that for wound foil types, modern replacement parts do not mark the outside foil, which needs to be at ground potential in many tube circuits, otherwise the circuit can pick up noise and hum). Funny that you mentioned that! I just watched a YouTube video today about how to experimentally determine which lead is connected to the outer foil for applications where that's important. Modern film caps may have a stripe on one end, but it doesn't appear to reliably indicate which lead goes to the outer foil. I've often wondered why they even bother to put that polarity stripe on modern film parts when it doesn't actually indicate the outside foil terminal. Maybe this is something that has become lost knowledge to manufacturers over the years to the point where even Vishay/Sprague doesn't know what that black indicator stripe was actually used for?
Re: PDP 11 gear finally moved
On Tue, 21 Jul 2015, ben wrote: On 7/21/2015 9:04 AM, Lyle Bickley wrote: IMHO, these "white papers" indicating that ALL aluminum electrolytic capacitors decay is obvious nonsense - based on real life experience - not someones theory... The whole problem with the caps is the water between foil. As modern caps use more and more tricks to improve the surface area,the water margin gets thinner and thinner.At least with GOOD vacuum tube equipment you could replace caps. One of those tricks they use in modern aluminum electrolytics is to emboss or etch the foil. This gives it more surface area, so they can use a smaller amount of foil and obtain the same capacitance. The foil and insulator in many modern parts is also much thinner.
Re: PDP 11 gear finally moved
On Tue, 21 Jul 2015, Mike Stein wrote: I suspect that the real criterion for whether to shotgun-replace caps is who is paying/getting paid for the materials and labour ;-). I dunno about that. When I've done commercial boards such as industrial process controllers and CPUs for customers with nearly unlimited funds, I charged the customer based on an hourly rate. Since I use a vacuum desoldering tool, changing out 10-15 aluminum electrolytics on a board took me not much more time than 1-2. Most of the time spent on a board that comes out of the field is spent on cleaning, testing (before and after repairs) and prep, and it only takes a few seconds to pull the solder off of a couple of component leads. Replacing aged electrolytics wholesale on these types of boards also meant I didn't need to worry that the same board would be back on my bench again in the next 3-6 months. These days, I'm not taking on any new commercial work though, there was just too much demand due to all those shoddy far-east made capacitors, and it meant I pushed aside all my own projects. I guess from a business standpoint, if I had been trying to make extra money on boards repeat failing in the field and having to come back in for repairs over and over, changing out only 1 or 2 aluminum electrolytics would have made sense. That said, industrial process equipment tends to run 24/7 and is expected to be 100% reliable. If something shuts down, it tends to cost a heck of a lot of money, so I would no doubt have lost many customers. FWIW I'm certainly not about to spend 100s of dollars, not to mention time spent in sourcing and replacing, to replace the caps in systems 100s? Where are you sourcing your components from? The typical board I rebuild has a component cost of about $20 or less. Smaller switchmode PSUs with a bunch of 10-18mm radials might be closer to $35-50. Larger PSUs /might/ cost closer to $100 if they have several large screw terminal capacitors in them. All things considered, that isn't very much money in today's dollars, and considering the full replacement cost of some of these boards (if they are even available), those preventive maintenance costs are an absolute bargain, /especially/ if you are doing the work yourself on your own time. that are running perfectly "just in case"... How do you -know- they are "running perfectly"? Just because a widget itself is functioning, you have no way of knowing if that capacitor is working 100% properly /unless/ you actually remove it from circuit and run a full battery of tests on it. Simply measuring the capacitance with a DMM while a capacitor is in circuit isn't good enough. Given that a typical aluminum electrolytic capacitor costs anywhere from $0.12-$0.15 (4mm or 5mm diameter radials) to about $1.00 (12mm or 16mm diameter radial), it also doesn't make much sense to desolder a 20 year old part, spend at a minimum 5 or more minutes testing it, and then solder it back in. It it much more economical to pull the old part and install a new one and be done with it. (You also don't have to worry if the desoldering and resoldering process might have damaged the original parts end-seals.) That said, I personally pre-test new parts, in bulk, before I put them into my stock, so I know ahead of time that I'm installing known-good parts. On many occasions I've cut open old aluminum electrolytics, and the guts very much do deteriorate with age. In addition to corrosion of the foil (black spots and pitting) and foil to terminal junctions (corrosion), one thing I particularly noticed was the more operating hours an aluminum electrolytic capacitor had on it, the more its electrolyte and paper insulator tended to smell bad compared to an otherwise identical (same brand and series) part that had very low hours. These are all clear signs of deterioration. To those who advocate keeping old aluminum electrolytics in service, I have to also ask, would you also try to recondition 20 year old NiCd or SLA batteries and keep those in service too? The bottom line really is, if you want something to be as reliable as you can possibly make it, you replace old aluminum electrolytic capacitors which are outside of their expected service life. If you don't care if something fails over and over, or you actually like to have the same widget on your service bench year after year, or month after month, you just replace 1 or 2.
RE: PDP 11 gear finally moved
Rich Alderson wrote: > >From: Peter Coghlan >Sent: Saturday, July 18, 2015 1:27 AM > >> Rich Alderson wrote: > It is generally a good idea to re-form electrolytic capacitors in power supplies, and to bench check the power supplies (under some kind of load) before actually applying power to the whole unit. > >>> It is always a good idea to replace electrolytic capacitors in power >>> supplies. >>> The rest of the advice is sound. > >> Can you please clarify if this statement represents the policy of the Living >> Computer Museum or is it something more personal? Perhaps some qualification >> or a re-phrasing would be useful as it does not appear to make sense as it >> stands? > >This is the policy of Living Computer Museum. It is based on the cumulative >experience of multiple very senior electrical engineers[1] doing restorations >here, in conjunction with industry white papers with tables of decay rates for >the aluminum electrolytics that indicate that, *no matter what*, they lose >capacitance over time, until c. 14 years from manufacturer date they are at 10% >of rating. > >When, in 2004, we first began restorations of the systems that eventually >became LCM, we followed the sage advice of those who described how to "re-form" >electrolytic capacitors. Months of frustrating results eventually led to the >search for industry literature on the topic; the result of that research was >the formulation of our policy regarding this practice--that it is not worth the >time and effort for minimal results. > >> I think you may have seen or participated in some of the many discussions we >> have had on this topic on this list? In light of these discussions, I find >> it >> hard to see how a categorical statement such as this one could be justified. > >Since the proponents of this practice make categorical statements with no >evidence that they want to listen to reasoned explanations, I long ago gave >over trying to convince them, and simply respond when someone makes a statement >to a newbie which will result in frustration and failure for the unfortunate >recipient of this advice. > > >Rich > > >[1] NB: I am not now, nor have I ever claimed to be, a hardware engineer of >any stripe, and more particularly not an electronics specialist. I am, >nonetheless, capable of reading and understanding research papers with >statistics that back up the claims being made even if I could not devise >the experiment to test them. I rely on my colleagues who are experts to >assure me that the writers are not smoking crack. > > >Rich Alderson >Vintage Computing Sr. Systems Engineer >Living Computer Museum >2245 1st Avenue S >Seattle, WA 98134 > >mailto:ri...@livingcomputermuseum.org > >http://www.LivingComputerMuseum.org/ > Hi Rich, Thank you for providing further clarification but please understand that I was trying to give you an opportunity to get out of the hole you were digging, not trying to encourage you to dig deeper. I was hoping to avoid going back over the issues which have been previously debated at length on the list without reaching any conclusions other than that different people have different strongly held views on the subject but I guess that was too much to hope for :-( Regards, Peter Coghlan.
Re: PDP 11 gear finally moved
On 7/21/2015 9:04 AM, Lyle Bickley wrote: IMHO, these "white papers" indicating that ALL aluminum electrolytic capacitors decay is obvious nonsense - based on real life experience - not someones theory... The whole problem with the caps is the water between foil. As modern caps use more and more tricks to improve the surface area,the water margin gets thinner and thinner.At least with GOOD vacuum tube equipment you could replace caps. Ben.
Re: PDP 11 gear finally moved
On 21/07/2015 06:14, Eric Smith wrote: On Mon, Jul 20, 2015 at 4:46 PM, Rich Alderson wrote: industry white papers with tables of decay rates for the aluminum electrolytics that indicate that, *no matter what*, they lose capacitance over time, until c. 14 years from manufacturer date they are at 10% of rating. That's very interesting. I haven't seen those white papers, but the "no matter what" must in fact depend on something, since on the PDP-1 Restoration Project we found that most of the 40 year old aluminum electrolytic capacitors still met their original specifications, including capacitance within rated tolerance. Yep, I find "no matter what" and "10%" very hard to believe for similar reasons. For one example, the aluminium electrolytics I recently took out of a 4-decade-old PDP-8/L were fine after reforming. In fact based on my tests I'd say they were well within their stated tolerance. My other PDP-8s, of not dissimilar vintage, are running fine. As is my c.2000 Origin 2000, my several other SGIs (some of which have been in regular use since the mid 90s, and two have been running 24/7 with only brief interruptions over that period), assorted PDP-11s, ... -- Pete Pete Turnbull
Re: PDP 11 gear finally moved
- Original Message - From: "Tothwolf" Sent: Monday, July 20, 2015 10:03 PM ... I too am getting tired of repeating the same thing over and over; compiling this sort of information in a single location might be helpful. As it happens I am getting tired of _reading_ the same thing over and over; another of those Windows/Linux, PC/Mac etc. debates that contribute little and never change anyone's opinion. By all means, compile a _balanced_ summary and host it somewhere for reference. I suspect that the real criterion for whether to shotgun-replace caps is who is paying/getting paid for the materials and labour ;-). FWIW I'm certainly not about to spend 100s of dollars, not to mention time spent in sourcing and replacing, to replace the caps in systems that are running perfectly "just in case"... m
Re: PDP 11 gear finally moved
On Mon, 20 Jul 2015 23:14:36 -0600 Eric Smith wrote: > On Mon, Jul 20, 2015 at 4:46 PM, Rich Alderson > wrote: > > industry white papers with tables of decay rates for > > the aluminum electrolytics that indicate that, *no matter what*, they lose > > capacitance over time, until c. 14 years from manufacturer date they are at > > 10% > > of rating. > > That's very interesting. I haven't seen those white papers, but the > "no matter what" must in fact depend on something, since on the PDP-1 > Restoration Project we found that most of the 40 year old aluminum > electrolytic capacitors still met their original specifications, > including capacitance within rated tolerance. Of the few electrolytic > capacitors that had failed, the problem was a catastrophic failure, > not the capacitance being outside the rated tolerance. > > In the PDP-1, we preferred to keep the original components as much as > possible. Had there been a capacitor, the failure which would have > caused extensive damage to other components, we would have given > serious consideration to replacing it. However, that was not the case > for any of the capacitors in the PDP-1. > > Had our analysis indicated any expected benefit to replacing all of > the electrolytic capacitors, we would have done so, and bagged and > tagged the originals similar to what we did with failed components, so > that they could be replaced if it ever was desired to return the > artifact to its pre-restoration condition. > > I'm not recommending against LCM's policy, but I also wouldn't > necessarily encourage anyone to adopt it, nor to adopt the practices > of the CHM PDP-1 Restoration Project, without studying the issue. As Eric, I'm a member of the PDP-1 Restoration Team. The PDP-1 restoration was completed in 2005 - and annually we check the power supplies for voltage, ripple, etc. Not one of the re-formed capacitors have failed in the ten years since the completion of the restoration. I also re-formed all P/S capacitors in my PDP-8/S in September, 2013. Not one has failed since... Same with my EAI TR-20 Analog computer. And so it is for all the systems in my collection... IMHO, these "white papers" indicating that ALL aluminum electrolytic capacitors decay is obvious nonsense - based on real life experience - not someones theory... Lyle -- 73 AF6WS Bickley Consulting West Inc. http://bickleywest.com "Black holes are where God is dividing by zero"
RE: PDP 11 gear finally moved
> From: a...@p850ug1.demon.co.uk > To: cctalk@classiccmp.org > Subject: RE: PDP 11 gear finally moved > Date: Sun, 19 Jul 2015 14:35:52 + > > > > > Be careful, static daamge does not always show up at the time. You can > damage an IC, have it work for some time afterwards and then fail. > I'm quite aware of that. I've looked under a microscopeat some parts that were mishandled but still working.For how long, one can only guess.Dwight > -tony
RE: PDP 11 gear finally moved
> > > But yes, selenium rectifiers rarely work now (although there are exceptions) > > and when they fail they can take out the mains transformer. And they smell > > horrible (think of school dinner cabbage!) > > Huh? All devices with selenium rectifiers that I/we own are OK. And a > selenium rectifier only fails if overloaded. See for example the power > supply of the LGP-30: I've had many more selenium rectifiers fail than electrolytics. But actually yes, I do still have some original selenium rectifiers in operation. Come to think of it, every UK Telephone 706, 746, 722, 776, etc (The common 1970's telephones) had a selenium rectifier stack ( 8 diodes) as part of the voltage regulator circuit. I have never heard of one of those failing. > And all my radio/TV sets with selenium rectifiers are OK, too. I had to > replace one in my TV as it had a too high resistance, but only because I > didn't know at that time that I could re-fasten the nuts of the rectifier > (selenium rectifier plates can suffer from contact resistances). The ones I mainly have are those flat 'contact cooled' ones that you bolt onto the chassis. You can take those apart and bend contacts, etc, but most of the time I replace them with a suitable silicon device. -tony
RE: PDP 11 gear finally moved
On Tue, 21 Jul 2015, tony duell wrote: But yes, selenium rectifiers rarely work now (although there are exceptions) and when they fail they can take out the mains transformer. And they smell horrible (think of school dinner cabbage!) Huh? All devices with selenium rectifiers that I/we own are OK. And a selenium rectifier only fails if overloaded. See for example the power supply of the LGP-30: http://computermuseum.informatik.uni-stuttgart.de/dev_en/lgp30/lgp30.html Note: the height is about 60cm, power rating IIRC somewhere between 500 and 1000W! And all my radio/TV sets with selenium rectifiers are OK, too. I had to replace one in my TV as it had a too high resistance, but only because I didn't know at that time that I could re-fasten the nuts of the rectifier (selenium rectifier plates can suffer from contact resistances). Christian
RE: PDP 11 gear finally moved
On Mon, 20 Jul 2015, Rich Alderson wrote: the aluminum electrolytics that indicate that, *no matter what*, they lose capacitance over time, until c. 14 years from manufacturer date they are at 10% of rating. Please excuse me, but this is utter nonsense. Most electrolytics in our machines are 30 years and older, and they just work. Those caps that I checked (mostly large filter/smoothing caps), e.g. those from the LGP-30 (nearly 60 years old) or Mincal 523 (44 years old), are just fine. Smaller ones don't even have to be bothered with. OTOH foil caps from the 50s/60s (e.g. ERO/EROFOL/EROID/Wima) tend to lose a bit of their isolation and become resistive (several MOhm). This can be a problem with AC coupling in tube circuits. Also problematic are more modern foil caps in line filters (e.g. X/Y caps), or even oil filled MP caps in power supply (magnetic constanters, filters) or motor applications (phase shifters). But admittedly I don't know what crappy electrolytics you have encountered in your "industry grade" machines. Or are we talking of modern machines (<30 years) ? [1] NB: I am not now, nor have I ever claimed to be, a hardware engineer of any stripe, and more particularly not an electronics specialist. I am, nonetheless, capable of reading and understanding research papers with statistics that back up the claims being made even if I could not devise the experiment to test them. I rely on my colleagues who are experts to assure me that the writers are not smoking crack. Statistics... don't believe any statistic that you haven't faked yourself. Honestly, IMO this doesn't really qualify you as expert in capacitors. I think those statistics are based on running the caps 24/7 at their nominal ratings, but surley they don't apply to moderate museum usage. Christian
RE: PDP 11 gear finally moved
On Sun, 19 Jul 2015, dwight wrote: I have rarely seen static damage to electronic parts. I can imagine that if I were in Nevada during winter time, I might see more. There were times when, even with a key to be the discharge point that my arm still jumped. On parts, the ones I've seen that I could definitely attribute to static were, VFets with no zener input protection and the CMOS parts, 4051, 4052 and 4053. The VFets were killed with soldering irons that someone cut the ground wires so I couldn't really say it was static in the normal sense. I doubt any power supply could ever be damage from a discharge to a output lead. The ratios of capacitance is too different. The human body just doesn't have enough capacitance to mean anything to a power supply filter capacitor. Now, if your talking lighting as the source of static, I've even seen those static protection parts blown off boards. Now that is static damage! Tinker Dwight Oddly enough, I have a Sangean ATS-803A (Radioshack DX-440) receiver on my bench right now which has static electricity damage. They used two Sony 2SK152 JFETs (long since discontinued and virtually impossible to source) which can be damaged by static electricity merely by touching the telescoping antenna. I've replaced the two 2SK152 with Fairchild J113 JFETs and retrofitted a pair of inverse-paralleled 1N4148 diodes just before the antenna selection switch (between ground and the switched side of the external antenna jack) to help prevent future damage to the replacement JFETs. The receiver still isn't working quite right just yet though. It currently works fine on broadcast AM up to 1620KHz (internal loopstick antenna) and broadcast FM with the external telescoping antenna, but at 1621KHz and above in AM mode, the set is totally deaf. It is supposed to use the external telescoping antenna for AM operation above 1620KHz, but there is still a faulty component somewhere in that portion of the circuit.
Re: PDP 11 gear finally moved
On Mon, Jul 20, 2015 at 4:46 PM, Rich Alderson wrote: > industry white papers with tables of decay rates for > the aluminum electrolytics that indicate that, *no matter what*, they lose > capacitance over time, until c. 14 years from manufacturer date they are at > 10% > of rating. That's very interesting. I haven't seen those white papers, but the "no matter what" must in fact depend on something, since on the PDP-1 Restoration Project we found that most of the 40 year old aluminum electrolytic capacitors still met their original specifications, including capacitance within rated tolerance. Of the few electrolytic capacitors that had failed, the problem was a catastrophic failure, not the capacitance being outside the rated tolerance. In the PDP-1, we preferred to keep the original components as much as possible. Had there been a capacitor, the failure which would have caused extensive damage to other components, we would have given serious consideration to replacing it. However, that was not the case for any of the capacitors in the PDP-1. Had our analysis indicated any expected benefit to replacing all of the electrolytic capacitors, we would have done so, and bagged and tagged the originals similar to what we did with failed components, so that they could be replaced if it ever was desired to return the artifact to its pre-restoration condition. I'm not recommending against LCM's policy, but I also wouldn't necessarily encourage anyone to adopt it, nor to adopt the practices of the CHM PDP-1 Restoration Project, without studying the issue. Eric
RE: PDP 11 gear finally moved
> I've not replaced any in a PDP11 power supply, however I have replaced > them in other equipment with equally large PSUs. In the odd case where a > computer grade screw terminal capacitor is extremely expensive or > completely unobtainable (those which I've purchased were under $20-30) I > might be willing to leave an original part in place, *if* it can pass a > leakage test. I was quoted over \pounds 30.00 each for the ones for DEC power bricks. No thanks. I've yet to have one fail in a couple of dozen of said regulator units. [...] > > Testing each aluminum electrolytic and wax paper capacitor vs replacing > them all doesn't seem to be the prevailing norm in the vintage radio > communities today. It is over here. > Yes, the grid cap would /usually/ be a non-polarized wax paper type, which > tend to be very unreliable. I've yet to find a wax paper type which will > pass a leak test and those are also on my replace on sight list. > > Of course you wouldn't want to replace mica, ceramic, or plastic film > parts without good reason, but if a set is going to be more than just a > shelf queen, aluminum electrolytics and wax paper capacitors are a It depends a lot on the circuit. If replacing the capacitor is going to involve major realignment and the original is probably OK and leakage is not going to do further damage (likely in the case of a tuning component) then I will leave it and only replace if it fails. > must-replace item. Carbon film resistors in this sort of equipment should > also be tested, however I only replace those which are either bad or out > of tolerance (some brands held up better than others). This is inconistent. A capacitor which is failing (starting to leak, say) may get worse. A resistor which is drifting may get worse. Either can do more damage when it fails. Why replace the cap and not the resistor? > > I probably would replace certain safety-related capacitors in live > > chassis sets, like ones that isolate external sockets, using class Y > > replacements. But that;s about it. > > That's a good idea, however something to keep in mind is that class Y > safety rated capacitors are not designed not to short (and not put say a I thought that was the difference between class X (will fail in a safe way, but may short) and class Y (will not short). The latter are to be used where 'failure of the capacitor may expose a person to electric shock' according to the data sheets I've read. In general class X go across the mains, class Y from mains to ground. > I consider replacing aluminum electrolytics to be preventive maintenance. > One wouldn't drive a 20-50 year old car with original hoses, belts, and > tires, and IMO it is just common sense to replace electronic components > such as aluminum electrolytic capacitors which have extremely well > documented life expectancies and failure rates. I do wonder if this data is based on the cheaper components used in consumer electronics (paticularly things like AA5s) and that the capacitors used in computers were of a much higher quality and longer life. > As far as shotgun-repairs go, one of my own pet peeves are those out there > selling "cap kits" (usually really low quality [sometimes counterfeit] Oh don't get me started > capacitors, too) to newbies which also include a bunch of semiconductors > (diodes, voltage regulators, and transistors) on the theory that those > parts fail because they run hot. I've gotten to the point where I will not > even attempt to service a board which has been botched up by a fat > fingered newbie who has attempted to install one of those kits. > > There is however one component besides certain capacitors which I > absolutely will replace on sight, no exceptions, period, and those are > selenium rectifiers. There is nothing good that can be said of selenium > rectifiers, and it is absolutely trivial to solder in a silicon diode as a > modern replacement. In some cases you need a series resistor to compensate for the forward resistance of the selenium rectifier or the output voltage goes too high. Particularly in those mains/battery valve radios with 1.5V directly heated valves that have filament burn-out if you look at them wrongly... But yes, selenium rectifiers rarely work now (although there are exceptions) and when they fail they can take out the mains transformer. And they smell horrible (think of school dinner cabbage!) -tony
RE: PDP 11 gear finally moved
On Mon, 20 Jul 2015, Rich Alderson wrote: On Sat, 18 Jul 2015, Peter Coghlan wrote: Rich Alderson wrote: It is generally a good idea to re-form electrolytic capacitors in power supplies, and to bench check the power supplies (under some kind of load) before actually applying power to the whole unit. It is always a good idea to replace electrolytic capacitors in power supplies. The rest of the advice is sound. Can you please clarify if this statement represents the policy of the Living Computer Museum or is it something more personal? Perhaps some qualification or a re-phrasing would be useful as it does not appear to make sense as it stands? This is the policy of Living Computer Museum. It is based on the cumulative experience of multiple very senior electrical engineers[1] doing restorations here, in conjunction with industry white papers with tables of decay rates for the aluminum electrolytics that indicate that, *no matter what*, they lose capacitance over time, until c. 14 years from manufacturer date they are at 10% of rating. [...] I think you may have seen or participated in some of the many discussions we have had on this topic on this list? In light of these discussions, I find it hard to see how a categorical statement such as this one could be justified. Since the proponents of this practice make categorical statements with no evidence that they want to listen to reasoned explanations, I long ago gave over trying to convince them, and simply respond when someone makes a statement to a newbie which will result in frustration and failure for the unfortunate recipient of this advice. Rich, Do you happen to have a list of whitepapers and/or links on hand? I too am getting tired of repeating the same thing over and over and compiling this sort of information in a single location might be helpful. Buried in my own archives I have quite a few papers and datasheets in pdf format, but they are all mixed in with everything else so finding them would be quite a challenge.
RE: PDP 11 gear finally moved
On Mon, 20 Jul 2015, tony duell wrote: Replace - yes, *especially* if you don't have a big budget. Aluminum electrolytic capacitors are CHEAP and easy to obtain. Replacement semiconductors by comparison are expensive and can be quite difficult to find. Err, have you priced the screw-terminal 'computer grade' electolytic capacitors that were used in these PDP11 power supplies. They are not cheap, if you can find them at all. And of course NOS ones might be as good or bad as the one that's already there. Conversely when I had a major disaster in a DEC power regulator brick some years ago (blew almost all the transistors and the 723) the replacement parts were easy to get (exact replacements, not just equivalents) and were not expensive. I've not replaced any in a PDP11 power supply, however I have replaced them in other equipment with equally large PSUs. In the odd case where a computer grade screw terminal capacitor is extremely expensive or completely unobtainable (those which I've purchased were under $20-30) I might be willing to leave an original part in place, *if* it can pass a leakage test. [...] Ironically, 20-30 years ago this same mindset used to persist with people who collected vacuum tube (valve) based radios and television, however that attitude no longer seems to be present in those communities today (not worth risking an irreplaceable transformer or inductor over $5.00-$10.00 worth of aluminum electrolytics). Odd... I know plenty of people who restore old valve radios and audio stuff and not one will blanket-replace all the aluminium electrolytics. There is a capacitor that I (and they) would check very carefully, but that's not an electrolytic. I refer of course to the coupling capacitor to output valve grid. In a lot of radios this is connected to the anode (plate) of the audio ampilfier triode so if it leaks it puts a +ve voltage on the output valve causing far too high an anode current there. But even then I (and everyone else I know) would test it, not just replace it. Some of those capacitors are very reliable and the replacements you get not any better. Testing each aluminum electrolytic and wax paper capacitor vs replacing them all doesn't seem to be the prevailing norm in the vintage radio communities today. Yes, the grid cap would /usually/ be a non-polarized wax paper type, which tend to be very unreliable. I've yet to find a wax paper type which will pass a leak test and those are also on my replace on sight list. Of course you wouldn't want to replace mica, ceramic, or plastic film parts without good reason, but if a set is going to be more than just a shelf queen, aluminum electrolytics and wax paper capacitors are a must-replace item. Carbon film resistors in this sort of equipment should also be tested, however I only replace those which are either bad or out of tolerance (some brands held up better than others). I probably would replace certain safety-related capacitors in live chassis sets, like ones that isolate external sockets, using class Y replacements. But that;s about it. That's a good idea, however something to keep in mind is that class Y safety rated capacitors are not designed not to short (and not put say a floating chassis at mains potential). Safety rated capacitors are instead designed to blow clear while not catching on fire (or otherwise be self-extinguishing), should they short out across mains potential. This means should a class Y part short, a floating chassis could still be placed at mains potential, and that capacitor is not going to blow clear. That said, anything is going to be better than a wax paper capacitor, and a class Y safety rated part is also much safer in this sort of application than a ceramic disc. Incidentally, do you shotgun-replace 7805s and other 3 terminal regulators? If not, why not? They can fail, and if they do they do a lot more damage than a failed capacitor. As a general rule, I do not make shotgun-repairs to electronic equipment. While I may replace certain failure-prone parts outright on sight, I still prefer to determine which part(s) are causing a malfunction. I consider replacing aluminum electrolytics to be preventive maintenance. One wouldn't drive a 20-50 year old car with original hoses, belts, and tires, and IMO it is just common sense to replace electronic components such as aluminum electrolytic capacitors which have extremely well documented life expectancies and failure rates. As far as shotgun-repairs go, one of my own pet peeves are those out there selling "cap kits" (usually really low quality [sometimes counterfeit] capacitors, too) to newbies which also include a bunch of semiconductors (diodes, voltage regulators, and transistors) on the theory that those parts fail because they run hot. I've gotten to the point where I will not even attempt to service a board which has been botched up by a fat fingered newbie who h
Re: PDP 11 gear finally moved
> On Jul 20, 2015, at 18:02 , Tothwolf wrote: > I replace wax paper types with polyester (mylar), polystyrene or ceramic > discs, depending on how they are used in the circuit (note however that for > wound foil types, modern replacement parts do not mark the outside foil, > which needs to be at ground potential in many tube circuits, otherwise the > circuit can pick up noise and hum). Funny that you mentioned that! I just watched a YouTube video today about how to experimentally determine which lead is connected to the outer foil for applications where that's important. Modern film caps may have a stripe on one end, but it doesn't appear to reliably indicate which lead goes to the outer foil. -- Mark J. Blair, NF6X http://www.nf6x.net/
Re: PDP 11 gear finally moved
On Mon, 20 Jul 2015, Mark J. Blair wrote: Now on the topic of capacitors: The only component type that I replace on sight at this point are the Rifa paper-dielectric EMI suppression caps. Had one go incendiary on me so far, and I do a replace-on-sight routine on them because my hypothesis of the failure mechanism(*) leads me to believe that they're all likely to burn up once the plastic shell has developed any cracks. They're easy to recognize: Rectangular, with transparent yellow plastic housings, which are usually crazed with fine cracks. Different caps which should not be subject to the same failure mechanism are easily available. (*) Paper dielectric is said to absorb moisture from the atmosphere if not sealed. So, I presume that once the yellow plastic shell cracks from old age, moisture gets in, and then the caps break down under power. I replace these with poly film safety-rated caps with suitable ratings, since the poly film shouldn't absorb significant moisture even if the housing seal fails. Absolutely! I didn't mention those in my previous list since I was focused on aluminum electrolytics, but those yellow Rifa parts are an especially sore spot in older test gear. My own theory on these is that the swelling of the paper is what is causing them to crack. I'm not sure what chemical they treat the paper with, but it apparently doesn't hold up long term and/or this is just their failure mode as they age and wear out. While Rifa still makes these very same safety capacitors, I've been replacing them with MKP types from TDK which won't fail in the same way. Oddly enough, those failing class X and class Y Rifa parts I see seem to be early 1980s to mid 1990s vintage gear, which puts them in that same 20-30 year age I tend to use for replacing aluminum electrolytics. Another capacitor type which I replace on sight are any wax paper capacitors such as you would find in tube (valve) based equipment. The wax coated tubular types are easy to spot, but the epoxy covered parts (black beauty, bumble bee, etc.) fail the same way. After replacing 100s, if not 1000s of the things over the years, I've yet to find one, even NOS (which always seem to turn up in lots of parts from estates and such), which would pass a leak test. I replace wax paper types with polyester (mylar), polystyrene or ceramic discs, depending on how they are used in the circuit (note however that for wound foil types, modern replacement parts do not mark the outside foil, which needs to be at ground potential in many tube circuits, otherwise the circuit can pick up noise and hum).
RE: PDP 11 gear finally moved
From: Peter Coghlan Sent: Saturday, July 18, 2015 1:27 AM > Rich Alderson wrote: >>> It is generally a good idea to re-form electrolytic capacitors in power >>> supplies, and to bench check the power supplies (under some kind of >>> load) before actually applying power to the whole unit. >> It is always a good idea to replace electrolytic capacitors in power >> supplies. >> The rest of the advice is sound. > Can you please clarify if this statement represents the policy of the Living > Computer Museum or is it something more personal? Perhaps some qualification > or a re-phrasing would be useful as it does not appear to make sense as it > stands? This is the policy of Living Computer Museum. It is based on the cumulative experience of multiple very senior electrical engineers[1] doing restorations here, in conjunction with industry white papers with tables of decay rates for the aluminum electrolytics that indicate that, *no matter what*, they lose capacitance over time, until c. 14 years from manufacturer date they are at 10% of rating. When, in 2004, we first began restorations of the systems that eventually became LCM, we followed the sage advice of those who described how to "re-form" electrolytic capacitors. Months of frustrating results eventually led to the search for industry literature on the topic; the result of that research was the formulation of our policy regarding this practice--that it is not worth the time and effort for minimal results. > I think you may have seen or participated in some of the many discussions we > have had on this topic on this list? In light of these discussions, I find it > hard to see how a categorical statement such as this one could be justified. Since the proponents of this practice make categorical statements with no evidence that they want to listen to reasoned explanations, I long ago gave over trying to convince them, and simply respond when someone makes a statement to a newbie which will result in frustration and failure for the unfortunate recipient of this advice. Rich [1] NB: I am not now, nor have I ever claimed to be, a hardware engineer of any stripe, and more particularly not an electronics specialist. I am, nonetheless, capable of reading and understanding research papers with statistics that back up the claims being made even if I could not devise the experiment to test them. I rely on my colleagues who are experts to assure me that the writers are not smoking crack. Rich Alderson Vintage Computing Sr. Systems Engineer Living Computer Museum 2245 1st Avenue S Seattle, WA 98134 mailto:ri...@livingcomputermuseum.org http://www.LivingComputerMuseum.org/
Re: PDP 11 gear finally moved
If I may go back to the original post topic for a moment, what model is that line printer that is pictured? I'm on the lookout for a DEC LP32 to go with my 11/730. Now on the topic of capacitors: The only component type that I replace on sight at this point are the Rifa paper-dielectric EMI suppression caps. Had one go incendiary on me so far, and I do a replace-on-sight routine on them because my hypothesis of the failure mechanism(*) leads me to believe that they're all likely to burn up once the plastic shell has developed any cracks. They're easy to recognize: Rectangular, with transparent yellow plastic housings, which are usually crazed with fine cracks. Different caps which should not be subject to the same failure mechanism are easily available. (*) Paper dielectric is said to absorb moisture from the atmosphere if not sealed. So, I presume that once the yellow plastic shell cracks from old age, moisture gets in, and then the caps break down under power. I replace these with poly film safety-rated caps with suitable ratings, since the poly film shouldn't absorb significant moisture even if the housing seal fails. -- Mark J. Blair, NF6X http://www.nf6x.net/
RE: PDP 11 gear finally moved
> > Replace - yes, *especially* if you don't have a big budget. Aluminum > electrolytic capacitors are CHEAP and easy to obtain. Replacement > semiconductors by comparison are expensive and can be quite difficult to > find. Err, have you priced the screw-terminal 'computer grade' electolytic capacitors that were used in these PDP11 power supplies. They are not cheap, if you can find them at all. And of course NOS ones might be as good or bad as the one that's already there. Conversely when I had a major disaster in a DEC power regulator brick some years ago (blew almost all the transistors and the 723) the replacement parts were easy to get (exact replacements, not just equivalents) and were not expensive. [...] > Ironically, 20-30 years ago this same mindset used to persist with people > who collected vacuum tube (valve) based radios and television, however > that attitude no longer seems to be present in those communities today > (not worth risking an irreplaceable transformer or inductor over > $5.00-$10.00 worth of aluminum electrolytics). Odd... I know plenty of people who restore old valve radios and audio stuff and not one will blanket-replace all the aluminium electrolytics. There is a capacitor that I (and they) would check very carefully, but that's not an electrolytic. I refer of course to the coupling capacitor to output valve grid. In a lot of radios this is connected to the anode (plate) of the audio ampilfier triode so if it leaks it puts a +ve voltage on the output valve causing far too high an anode current there. But even then I (and everyone else I know) would test it, not just replace it. Some of those capacitors are very reliable and the replacements you get not any better. I probably would replace certain safety-related capacitors in live chassis sets, like ones that isolate external sockets, using class Y replacements. But that;s about it. Incidentally, do you shotgun-replace 7805s and other 3 terminal regulators? If not, why not? They can fail, and if they do they do a lot more damage than a failed capacitor. -tony
Re: PDP 11 gear finally moved
On 07/19/2015 02:03 AM, tony duell wrote: So, tony, if I'm correct, you just called "bullshit", right? I assume this relates to my comments on static damage of PDP11 PSUs, I am not sure I would quite put it that way (not on a public list :-)) but (a) I have never seen a DEC PSU (in a PDP11 or elsewhere) damaged by static, certainly not to external connections and (b) there were some many PDP11 PSUs with totally different design topologies that it would appear to be impossible to generalise like that. -tony Yeah, that would be it. Not sure what happened to the message I was replying to, should have been included -- --- Dave Woyciesjes --- CompTIA A+ Certified IT Tech - http://certification.comptia.org/ --- HDI Certified Support Center Analyst - http://www.ThinkHDI.com/ Registered Linux user number 464583 "Computers have lots of memory but no imagination." "The problem with troubleshooting is that trouble shoots back." - from some guy on the internet.
Re: PDP 11 gear finally moved
Well, all I can say is that my experience differs. I have had newer capacitors fail, and old ones, too, of course, but nothing points to wholesale replacement as a cost or time effective strategy, especially on something like an Altair. FWIW, I don't run my vintage machines all that often. Of course reforming a bad capacitor, whatever the failure mode, is going to be useless. Tothwolf wrote: >On Fri, 17 Jul 2015, Jay Jaeger wrote: >> On 7/17/2015 1:33 PM, Rich Alderson wrote: >> It is generally a good idea to re-form electrolytic capacitors in power supplies, and to bench check the power supplies (under some kind of load) before actually applying power to the whole unit. >>> >>> It is always a good idea to replace electrolytic capacitors in power >>> supplies. The rest of the advice is sound. >>> >> Replace - no, I don't agree - especially not for those of us who don't >> have the kind of budget that your organization has. In my experience, >> for equipment of this quality and vintage, 95% or more of the time an >> hour to a few hours of re-forming is all that is necessary - and as Tony >> has pointed out, even that is not often really necessary. > >Replace - yes, *especially* if you don't have a big budget. Aluminum >electrolytic capacitors are CHEAP and easy to obtain. Replacement >semiconductors by comparison are expensive and can be quite difficult to >find. > >While it might be worthwhile reforming a special purpose NOS electrolytic >that isn't much older than 15-20 years old, reforming 20-30 year old >heavily used (read: past usable service life; evaporation of the >electrolyte, corrosion of the foils and especially foil to terminal >junctions, etc) is a complete and total waste of time. > >Ironically, 20-30 years ago this same mindset used to persist with people >who collected vacuum tube (valve) based radios and television, however >that attitude no longer seems to be present in those communities today >(not worth risking an irreplaceable transformer or inductor over >$5.00-$10.00 worth of aluminum electrolytics).
RE: PDP 11 gear finally moved
On Fri, 17 Jul 2015, tony duell wrote: Perhaps. But not all of it, certainly. I'm currently four for four fixing dead flatscreens by re-capping their power supplies; I imagine others have similar experiences. It's not a huge stretch to imagine This could be taken to show that modern capacitors are not reliable, and given that there are plenty of 40-year-old ones still in use in various classic computers here it would be better to leave them as-is It really depends. If I'm having to replace filter capacitors in a faulty PSU or monitor, even if I've isolated the problem to one or two capacitors, I would be a fool not to replace them all because the next part that fails will be one of those which I didn't replace (been there, done that, own the tee shirt). A standard 85C or 65C rated 20-30 year old aluminum electrolytic is simply past its useful service life. More seriously, a lot of modern consumer stuff seems to have marginally-rated capacitors (and the use of 85 degree ones doesn't help). Possibly on those it is a good idea to replace them. But the ones in PDP11s were good quality at the start and were over-spec'd in general. With modern electronics, there are high quality parts and there are really cheap parts. Even though the high quality parts are about the same price as the really cheap parts when purchased in small quantity (in the one-off to a few 1000 quantity), profit-driven consumer electronics manufacturers are still going to use the cheaper parts when they can save even $0.01 or $0.005 per component or even a few cents on the overall cost of the complete widget. Many of these manufacturers also design their widgets to last for the warranty term and no more. If the consumer gets 2-3 years or more out of said widget, those manufacturers consider it a loss in terms of potential profits. In these cases, wholesale replacement of really cheap capacitors with high quality versions from top tier manufacturers (Panasonic, Nichicon, Rubycon, etc) can be a /really/ good idea. That said, even the top-tier capacitor manufacturers have lower end lines of parts, so it pays to do your homework and choose a longer life (usually lower ESR, meaning less internal heating and thus longer service life) part when sourcing replacements. Even vintage Mallory and Sprague parts are not without their faults. I recently replaced a bunch of early 1980s era Mallory capacitors which tested good, but when desoldered from the board, had brown crusty stuff around the safety vent in their bottom rubber seals. They might have continued to work "ok" for another year or even 10 years, but the high quality replacement parts I put in will be good for at least another 20-30 years. (The replacement parts also worked better as the DC rails had lower ripple after they were installed). that other power supplies may have similar issues; even if it turns out to not be the case, there is probably at least a little "can't hurt anything, right?" running around. Ah but it can hurt. Damage to the PCB (unlikely, sure), the new part might be faulty and thus introduce more faults, you might make an error fitting it, and so on. I prefer to only replace that which needs replacing. It really is a case by case basis, however in PSUs, CRT monitors, and similar where the components are exposed to higher temperatures, it really makes sense to replace 20-30 year old aluminum electrolytics wholesale. I guess another way to look at it is that an electronic device might still be functioning with old aluminum electrolytic capacitors, but is it still functioning as good as it was when it was new? A vintage device might have used really high quality aluminum electrolytics when it was made, but even high quality parts have a finite service life. What you have to decide is where to draw the when considering wholesale replacement of aluminum electrolytics, which with vintage electronics, I've found tends to be somewhere around the 20-30 year point.
Re: PDP 11 gear finally moved
On Fri, 17 Jul 2015, Todd Killingsworth wrote: I suspect part of the "swap'em ALL out" mentality comes from the 90's when some botched industrial espionage had some of the bottom-tier cap manufacturers using a dodgy electrolytic formula for their caps. These caps would have a frequent failure rate.. No. It is because the typical aluminum electrolytic capacitor at 20-30 years old is simply past its useful service life. At that point they tend to suffer from all sorts of issues and can no longer be considered reliable. That whole "botched industrial espionage" thing is also somewhat of a myth. There have been at least 3 different cases where there have been industry wide problems with aluminum electrolytics. The earliest I tend to see are the first generation SMD aluminum electrolytics from the late 1980s to about 1993. Those have problems with their rubber seals due to the rubber compound breaking down either due to the temperature they were reflow soldered at or because the boards were cleaned with chlorinated solvents. Newer SMD aluminum electrolytics do not have this problem (and capacitor manufacturers explicitly warn against using chlorinated solvents to clean pc boards). The second were those which you are referring to above, aka the "capacitor plague". Those started showing up in the marketplace around about 2000 and were mostly gone by about 2005. The third were the ultra-low ESR types from certain major manufacturers. The most common I dealt with were Nippon Chemicon KZG and KZJ (all of them, replace them wholesale on sight) and a batch of Nichicon HN and HM (only a certain date range were affected). The Nippon parts are of a faulty design (which Nippon never would admit to it, instead they tried to wipe all data about them from their site) while the affected Nichicon HN and HM parts were supposedly just overfilled with electrolyte (according to Nichicon). While not an issue for pre-90's electronics, it has fostered the mentality of full replacement for 'newer' electronics i.e. arcade/pinball machines I don't know how much equipment you service, but equipment made in the 80s pretty much needs replacement aluminum electrolytics today if it has many hours on it and/or it needs to remain reliable. I have a number of early '80s monitors and PSUs currently in my repair queue which only need replacement electrolytic capacitors (distorted picture, excessive ripple, etc).
Re: PDP 11 gear finally moved
On Fri, 17 Jul 2015, Jay Jaeger wrote: On 7/17/2015 1:33 PM, Rich Alderson wrote: It is generally a good idea to re-form electrolytic capacitors in power supplies, and to bench check the power supplies (under some kind of load) before actually applying power to the whole unit. It is always a good idea to replace electrolytic capacitors in power supplies. The rest of the advice is sound. Replace - no, I don't agree - especially not for those of us who don't have the kind of budget that your organization has. In my experience, for equipment of this quality and vintage, 95% or more of the time an hour to a few hours of re-forming is all that is necessary - and as Tony has pointed out, even that is not often really necessary. Replace - yes, *especially* if you don't have a big budget. Aluminum electrolytic capacitors are CHEAP and easy to obtain. Replacement semiconductors by comparison are expensive and can be quite difficult to find. While it might be worthwhile reforming a special purpose NOS electrolytic that isn't much older than 15-20 years old, reforming 20-30 year old heavily used (read: past usable service life; evaporation of the electrolyte, corrosion of the foils and especially foil to terminal junctions, etc) is a complete and total waste of time. Ironically, 20-30 years ago this same mindset used to persist with people who collected vacuum tube (valve) based radios and television, however that attitude no longer seems to be present in those communities today (not worth risking an irreplaceable transformer or inductor over $5.00-$10.00 worth of aluminum electrolytics).
RE: PDP 11 gear finally moved
> > I have rarely seen static damage to electronic parts. I can imagine > that if I were in Nevada during winter time, I might see more. There > were times when, even with a key to be the discharge point that > my arm still jumped. Be careful, static daamge does not always show up at the time. You can damage an IC, have it work for some time afterwards and then fail. > On parts, the ones I've seen that I could definitely attribute to static > were, VFets with no zener input protection and the CMOS parts, > 4051, 4052 and 4053. > The VFets were killed with soldering irons that someone cut the > ground wires so I couldn't really say it was static in the normal sense. > I doubt any power supply could ever be damage from a discharge > to a output lead. The ratios of capacitance is too different. The human > body just doesn't have enough capacitance to mean anything to > a power supply filter capacitor. Yes. Static electricity is not magic. It follows well-known physical laws. In particular, Q=C*V (using the normal definitions). When you put a static charge on the human body, the voltage is high becuase the capacitance (to ground) is low. If you then touch something, effectively its capacitance is in parallel with yours. The charge redistributes as a result. If the touched thing has a low capacitance, like the input to a MOSFET or CMOS gate (which you want to be low capacitance in normal use so you can charge/discharge it quickly to switch said device) then the voltage remains high. Zap!. If you touch the output of a PSU with around 1millifarad of capacitance to ground then quite simply you are not carrying enough charge to put a damaging voltage on it. OK, the inductance of the circuit makes a bit of difference (it will slow down the charging of said capacitor so the voltage may have a small peak above the steady state) but it is not going to make that much difference. Put it this way, if you connect a 1000uF capacitor across something (as is done on the outputs of these PSUs) and can damage it by static from a human body I will be very surprised. Now let's look at the PDP11/34 PSU regulators. What is in there? Some bipolar transistors, including power types. And normal semiconductor diodes. Not things that are commonly thought of as very static sensitive. A 723 bipolar IC. Never heard of that being damaged by static either. And that's about it. As I have said before, I don't know about the later PSUs. It's possible the SMPSUs in say a PDP11/94 do have problems from static damage (although I seriously doubt it's caused by touching external connections). But not the 11/34 supply. > Now, if your talking lighting as the source of static, I've even seen > those static protection parts blown off boards. > Now that is static damage! Oh sure. No PSU is going to take a lightening strike on input or output. Even a strike nearby might cause a lot of damage. But I don't think that's what we are talking about. -tony
RE: PDP 11 gear finally moved
I have rarely seen static damage to electronic parts. I can imagine that if I were in Nevada during winter time, I might see more. There were times when, even with a key to be the discharge point that my arm still jumped. On parts, the ones I've seen that I could definitely attribute to static were, VFets with no zener input protection and the CMOS parts, 4051, 4052 and 4053. The VFets were killed with soldering irons that someone cut the ground wires so I couldn't really say it was static in the normal sense. I doubt any power supply could ever be damage from a discharge to a output lead. The ratios of capacitance is too different. The human body just doesn't have enough capacitance to mean anything to a power supply filter capacitor. Now, if your talking lighting as the source of static, I've even seen those static protection parts blown off boards. Now that is static damage! Tinker Dwight
RE: RE: PDP 11 gear finally moved
> > So, tony, if I'm correct, you just called "bullshit", right? I assume this relates to my comments on static damage of PDP11 PSUs, I am not sure I would quite put it that way (not on a public list :-)) but (a) I have never seen a DEC PSU (in a PDP11 or elsewhere) damaged by static, certainly not to external connections and (b) there were some many PDP11 PSUs with totally different design topologies that it would appear to be impossible to generalise like that. -tony
Re: RE: PDP 11 gear finally moved
So, tony, if I'm correct, you just called "bullshit", right? -- --- Dave Woyciesjes --- ICQ# 905818 --- CompTIA A+ Certified IT Tech -http://certification.comptia.org/--- HDI Certified Support Center Analyst -http://www.ThinkHDI.com/Registered Linux user number 464583 "Computers have lots of memory but no imagination." "The problem with troubleshooting is that trouble shoots back." - from some guy on the internet.
Re: PDP 11 gear finally moved
Thank you all for the information. Ive been speaking with Paul Anderson on the phone, he went into great detail a general overview on how to get the machine apart and general beginner details. He referred me to the appropriate Documents on bitsavers, plan is to pick up some packs of paper and get them printed out tonight. On Sat, Jul 18, 2015 at 4:26 AM, Peter Coghlan wrote: > Rich Alderson wrote: > > > > > It is generally a good idea to re-form electrolytic capacitors in power > > > supplies, and to bench check the power supplies (under some kind of > > > load) before actually applying power to the whole unit. > > > > It is always a good idea to replace electrolytic capacitors in power > supplies. > > The rest of the advice is sound. > > > >Rich > > > > Rich Alderson > > Vintage Computing Sr. Systems Engineer > > Living Computer Museum > > 2245 1st Avenue S > > Seattle, WA 98134 > > > > mailto:ri...@livingcomputermuseum.org > > > > http://www.LivingComputerMuseum.org/ > > Rich, > > Can you please clarify if this statement represents the policy of the > Living > Computer Museum or is it something more personal? Perhaps some > qualification > or a re-phrasing would be useful as it does not appear to make sense as it > stands? > > I think you may have seen or participated in some of the many discussions > we > have had on this topic on this list? In light of these discussions, I > find it > hard to see how a categorical statement such as this one could be > justified. > > Regards, > Peter Coghlan. > On Sat, Jul 18, 2015 at 4:26 AM, Peter Coghlan wrote: > Rich Alderson wrote: > > > > > It is generally a good idea to re-form electrolytic capacitors in power > > > supplies, and to bench check the power supplies (under some kind of > > > load) before actually applying power to the whole unit. > > > > It is always a good idea to replace electrolytic capacitors in power > supplies. > > The rest of the advice is sound. > > > >Rich > > > > Rich Alderson > > Vintage Computing Sr. Systems Engineer > > Living Computer Museum > > 2245 1st Avenue S > > Seattle, WA 98134 > > > > mailto:ri...@livingcomputermuseum.org > > > > http://www.LivingComputerMuseum.org/ > > Rich, > > Can you please clarify if this statement represents the policy of the > Living > Computer Museum or is it something more personal? Perhaps some > qualification > or a re-phrasing would be useful as it does not appear to make sense as it > stands? > > I think you may have seen or participated in some of the many discussions > we > have had on this topic on this list? In light of these discussions, I > find it > hard to see how a categorical statement such as this one could be > justified. > > Regards, > Peter Coghlan. >
Re: PDP 11 gear finally moved
More myths and ledgends. As I remember it this all started with the arrival of FET's having a very high input impedance due to narrow gate areas. If you were daft enough not to have a path to earth and let a charge build up on the gate then you could exceed the breakdown voltage across the junction. I used to see the DEC field service statistics and PSU failures due to static build up were rare. Blown filter capacitors and burned up resistors were more the norm. TTL was was not imune to over voltage but not via static build up. Think about a CRT VDU. lots of high voltage and static but no charge up related failures. Rod Smallwood On 18/07/2015 20:31, tony duell wrote: Oh, sorry, didn't realize they used switchers for the PDP-11s. There have been _many_ DEC PSU designed used for the PDP11. I think all of them used some kind of switching regulator for the +5V line. A quick glance at the printsets will settle it.. However I was talking with a friend of mine last night about my error, and he told me that the switching supplies for the PDP-11s were very unreliable back in the day. He often had to troubleshoot the machines back then. A common failure was caused by static electric shock to the machine would blow the supply. NO carpets allowed!! That is (a) meaningless and (b) totally contrary to mine (and others) experiences. It's meaningless because there are so many 'PDP11' power supplies. There are some which use a mains transformer followed by step-down switching regulators. There are some which are more conventional SMPSUs, rectifying the mains and chopping the 350V so produced. There are some which are multiple versions of that in one box (and at least one of those has a switching supply running off the 350V DC rail which produces a single 36V output which is then regulated with more switching regulators). I do not believe all those designs have the same failure modes, or responses to static damage. However, I have worked on many PDP11s, with all sorts of PSUs. Now admittedly I am careful about static, even working on bipolar circuitry. But not to the point of being silly about it. And I will state that I have never damaged (or even caused to trip) a PDP11 PSU by a static zap to any of the output rails. And if a static zap to the casing of the machine damages the supply I would want to check the mains earthing (grounding) -- preferably before a fault causes somebody to get killed. -tony
RE: PDP 11 gear finally moved
> > Oh, sorry, didn't realize they used switchers for the PDP-11s. There have been _many_ DEC PSU designed used for the PDP11. I think all of them used some kind of switching regulator for the +5V line. A quick glance at the printsets will settle it.. > However I was talking with a friend of mine last night about my error, > and he told me that the switching supplies for the PDP-11s were very > unreliable back in the day. He often had to troubleshoot the machines > back then. A common failure was caused by static electric shock to the > machine would blow the supply. NO carpets allowed!! That is (a) meaningless and (b) totally contrary to mine (and others) experiences. It's meaningless because there are so many 'PDP11' power supplies. There are some which use a mains transformer followed by step-down switching regulators. There are some which are more conventional SMPSUs, rectifying the mains and chopping the 350V so produced. There are some which are multiple versions of that in one box (and at least one of those has a switching supply running off the 350V DC rail which produces a single 36V output which is then regulated with more switching regulators). I do not believe all those designs have the same failure modes, or responses to static damage. However, I have worked on many PDP11s, with all sorts of PSUs. Now admittedly I am careful about static, even working on bipolar circuitry. But not to the point of being silly about it. And I will state that I have never damaged (or even caused to trip) a PDP11 PSU by a static zap to any of the output rails. And if a static zap to the casing of the machine damages the supply I would want to check the mains earthing (grounding) -- preferably before a fault causes somebody to get killed. -tony
Re: PDP 11 gear finally moved
On 07/17/2015 11:17 PM, tony duell wrote: On the other hand if the +5V line did get too high it could have wiped out just about every IC in the unit. Ouch!. I've only ever had this happen once, and it was in a much lesser machine than a PDP11 (fortunately). Many years ago, I managed to feed +12V into an Acorn Atom which was expecting +5V (the on-board regulators were bypassed to allow it to run from an external regulated 5V PSU, rather than the usual unregulated +9V). Amazingly, it survived - although it makes me wonder if the experience dramatically reduced the lifespan of the TTL ICs though, even if they didn't immediately show any failure. cheers Jules
Re: PDP 11 gear finally moved
Oh, sorry, didn't realize they used switchers for the PDP-11s. However I was talking with a friend of mine last night about my error, and he told me that the switching supplies for the PDP-11s were very unreliable back in the day. He often had to troubleshoot the machines back then. A common failure was caused by static electric shock to the machine would blow the supply. NO carpets allowed!! John :-#)# On 07/17/2015 2:19 PM, Jay Jaeger wrote: U - his PDP-11/34 most certainly does use switching power regulators. ;) On 7/17/2015 4:06 PM, John Robertson wrote: On 07/17/2015 11:53 AM, Mouse wrote: I do find this witch-hunt against capacitors to be curious, given how few I've found to have failed. I suspect a lot of it comes from audiophools who think this is the way to fix anything... Perhaps. But not all of it, certainly. I'm currently four for four fixing dead flatscreens by re-capping their power supplies; I imagine others have similar experiences. It's not a huge stretch to imagine that other power supplies may have similar issues; even if it turns out to not be the case, there is probably at least a little "can't hurt anything, right?" running around. /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTMLmo...@rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B This is not surprising given the vintages of the machines. Modern machines using switching power supplies (15kHz+) must have capacitors with low ESR and high capacity to run properly. Older linear power supplies ran at 50/60hz and as such the capacitors had much less ripple current (and low frequency to boot) to deal with and the engineers typically over designed the values of capacitors to allow for some degradation. The machines you are playing with cost fortunes back in the day - they HAD to be reliable as possible. Modern caps run at or near their rated temperature (105C) last around 1,000 to 5,000 hours. The old linear supplies rarely heated the caps much over 40C and thus the caps would last decades...I put fans on our LCD monitors in our games and they last just fine. No fan? Expect a year or two at most before failure. John :-#)#
RE: PDP 11 gear finally moved
Rich Alderson wrote: > > > It is generally a good idea to re-form electrolytic capacitors in power > > supplies, and to bench check the power supplies (under some kind of > > load) before actually applying power to the whole unit. > > It is always a good idea to replace electrolytic capacitors in power supplies. > The rest of the advice is sound. > >Rich > > Rich Alderson > Vintage Computing Sr. Systems Engineer > Living Computer Museum > 2245 1st Avenue S > Seattle, WA 98134 > > mailto:ri...@livingcomputermuseum.org > > http://www.LivingComputerMuseum.org/ Rich, Can you please clarify if this statement represents the policy of the Living Computer Museum or is it something more personal? Perhaps some qualification or a re-phrasing would be useful as it does not appear to make sense as it stands? I think you may have seen or participated in some of the many discussions we have had on this topic on this list? In light of these discussions, I find it hard to see how a categorical statement such as this one could be justified. Regards, Peter Coghlan.
Re: PDP 11 gear finally moved
What I am wondering about, though, is the extra current they draw while they are forming up while the power supply is running. The capacitor might survive it (not get so hot that it fails), but the things supply the higher than ordinary current to it might not. Killed a bridge rectifier on a PDP-12 that way. JRJ On 7/17/2015 1:31 PM, tony duell wrote: > >> It is generally a good idea to re-form electrolytic capacitors in power >> supplies, and to bench check the power supplies (under some kind of >> load) before actually applying power to the whole unit. > > I am not sure either would have done much good here. The OP said it > ran OK for an hour or so, when you test a PSU on dummy load you > typically do it for a lot less time than that, Incidentally, DEC PSUs > of this type run fine with no load in my experience > > Also I have found the capacitors in these units to be very reliable. They > can fail, of course, but virtually all the DEC bricks I have are on their > original capacitors. I think I've replaced more chopper transistors than > capacitors in these. > > -tony >
RE: PDP 11 gear finally moved
> U - his PDP-11/34 most certainly does use switching power > regulators. ;) True, but I still haven't had major capacitor problems in one. -tony
RE: PDP 11 gear finally moved
> > I had to do some cap replacement on some older Motorola tube radios,I have > some basic soldering skills. I was under the impression that the capacitors > in computer equipment this big from this year would have been of better > quality and it would not be an issue. In general I will agree with that. Of course a capacitor can fail, but it is not that common. I certainly have never felt the need to 'recap' a classic computer PSU > I have someone scheduled to come out tonight after i get off work and get > it out of the rack. You do not need to remove the complete CPU from the rack. DEC machines of this vintage were made to be repaired. The CPU (assuming it's the 10.5" high box) will slide out on slide rails, and there are catches to let you turn it so that the front panel points upwards. With the CPU in various positions you can remove just about any part of it without taking it out of the rack. In fact having it in the rack makes things easier in some cases. Basically, you take the top and bottom covers off, then the top cover of the power supply. Tip the CPU up, then unplug the cables on the distribution panel under the machine (6 pin and 15 pin connectors). You can now test the PSU on its own. If you have to go further you will see that the PSU is fixed to the rest of the CPU box by 3 screws each side. If you take out the bottom 2 each side and loosen the top one it will hinge away (the metal is cut to allow this) and you can get to the fixing screws and connectors for the regulator modules. If you need to remove the unit under the transformer, you unplug the cables, undo 3 or 4 screws, and it slides out rearwards. Of course you unplug the mains cable before working on anything and only plug it in when you need to do some tests. But unlike more modern SMPSUs, there are no lethal stored voltages in this unit. -tony
RE: PDP 11 gear finally moved
> Thank you for the detailed information. I need to figure out how im going > to get it out of the rack and moved to a place where i can test it over the > next couple days where it will not be in the way. Ill find some way to do > a dummy load and do an extended test to be sure the supply is working > properly. All fingers crossed, god it better not have damaged any of the > boards, i do not know where i would get replacements.It took years for me DEC PSUs of that vintage have a crowbar circuit which effectively short-circuits the PSU (using an SCR) if the voltage rises too high to protect the rest of the machine. On the other hand if the +5V line did get too high it could have wiped out just about every IC in the unit. Ouch!. I've only ever had this happen once, and it was in a much lesser machine than a PDP11 (fortunately). > to get the machine, who knows how long it would take to find a specific > board that is bad. I did buy an oscillicope and a logic analyzer well in In general you should be thinking of repairing these machines on the component rather than board level. You may well have difficulty in finding a particular board (and how do you know that the replacement is good?) but finding one of the logic ICs is very easy. > advance in preparation for getting this machine, however short of pressing > the power button no clue how to use them or basic troubleshooting > procedures. Guess i just have to learn by doing That's how quite a few of us (including myself) learnt... The basic procedure that I use goes like this : 1) What should the machine be doing? In other words, from the schematics I deduce that there should be a clock signal on 'that wire' or data flowing there with enable pulses on that pin. 2) What is the machine doing (determined by examining said signals with a 'scope and LA) 3) Why the difference? If they are the same then that part of the machine is mostly working properly. If not, then what could explain what I am seeing, How can I determine what the cause is? Aha... What is _that_ signal doing? Check it -tony
Re: PDP 11 gear finally moved
U - his PDP-11/34 most certainly does use switching power regulators. ;) On 7/17/2015 4:06 PM, John Robertson wrote: > On 07/17/2015 11:53 AM, Mouse wrote: >>> I do find this witch-hunt against capacitors to be curious, given how >>> few I've found to have failed. I suspect a lot of it comes from >>> audiophools who think this is the way to fix anything... >> Perhaps. But not all of it, certainly. I'm currently four for four >> fixing dead flatscreens by re-capping their power supplies; I imagine >> others have similar experiences. It's not a huge stretch to imagine >> that other power supplies may have similar issues; even if it turns out >> to not be the case, there is probably at least a little "can't hurt >> anything, right?" running around. >> >> /~\ The ASCII Mouse >> \ / Ribbon Campaign >> X Against HTMLmo...@rodents-montreal.org >> / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B >> > > This is not surprising given the vintages of the machines. Modern > machines using switching power supplies (15kHz+) must have capacitors > with low ESR and high capacity to run properly. > > Older linear power supplies ran at 50/60hz and as such the capacitors > had much less ripple current (and low frequency to boot) to deal with > and the engineers typically over designed the values of capacitors to > allow for some degradation. The machines you are playing with cost > fortunes back in the day - they HAD to be reliable as possible. > > Modern caps run at or near their rated temperature (105C) last around > 1,000 to 5,000 hours. The old linear supplies rarely heated the caps > much over 40C and thus the caps would last decades...I put fans on our > LCD monitors in our games and they last just fine. > > No fan? Expect a year or two at most before failure. > > John :-#)# >
Re: PDP 11 gear finally moved
I tend to agree with your hunch. On 7/17/2015 1:55 PM, Todd Killingsworth wrote: > I suspect part of the "swap'em ALL out" mentality comes from the 90's when > some botched industrial espionage had some of the bottom-tier cap > manufacturers using a dodgy electrolytic formula for their caps. These > caps would have a frequent failure rate.. > > While not an issue for pre-90's electronics, it has fostered the mentality > of full replacement for 'newer' electronics i.e. arcade/pinball machines > > Todd Killingsworth > > On Fri, Jul 17, 2015 at 2:42 PM, tony duell wrote: > >>> It is generally a good idea to re-form electrolytic capacitors in power supplies, and to bench check the power supplies (under some kind of load) before actually applying power to the whole unit. >>> >>> It is always a good idea to replace electrolytic capacitors in power >> supplies. >> >> Could you, please, explain why? And how often should this be done? Every >> week, every month, every year, or what? >> >> FWIW, the number PSU elecrtrolytics I have replaced can be counted on the >> fingers of >> one hand -- in unary. Well, perhaps both hands. But it's <1% of all the >> PSU electrolytic >> capacitors I own. >> >> Only 2 cases spring to mind : >> >> The PSU in my 11/44 had a high ESR capacitor on the +36V rail (all other >> caps in the machine >> were fine) >> >> I changed the 2 mains smoothing capacitors in my HP120 not because they >> were electrically >> defective (they tested fine) but because one was bulging a little on top >> and had it exploded it would >> have hit the neck of the CRT with all the problems that would be likely to >> cause. >> >> I do find this witch-hunt against capacitors to be curious, given how few >> I've found to have >> failed. I suspect a lot of it comes from audiophools who think this is the >> way to fix anything... >> >> -tony >> >
Re: PDP 11 gear finally moved
That might be a little different -- much more recent - presumably in the ear of flat screens and PCs where there have been times when manufacturers got fed bad capacitors for their boards - which then failed later. IBM replaced a whole series of motherboards in one organization that I worked at because of that (though those were not power supply capacitors.) On 7/17/2015 1:53 PM, Mouse wrote: >> I do find this witch-hunt against capacitors to be curious, given how >> few I've found to have failed. I suspect a lot of it comes from >> audiophools who think this is the way to fix anything... > > Perhaps. But not all of it, certainly. I'm currently four for four > fixing dead flatscreens by re-capping their power supplies; I imagine > others have similar experiences. It's not a huge stretch to imagine > that other power supplies may have similar issues; even if it turns out > to not be the case, there is probably at least a little "can't hurt > anything, right?" running around. > > /~\ The ASCII Mouse > \ / Ribbon Campaign > X Against HTML mo...@rodents-montreal.org > / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B >
Re: PDP 11 gear finally moved
Replace - no, I don't agree - especially not for those of us who don't have the kind of budget that your organization has. In my experience, for equipment of this quality and vintage, 95% or more of the time an hour to a few hours of re-forming is all that is necessary - and as Tony has pointed out, even that is not often really necessary. JRJ On 7/17/2015 1:33 PM, Rich Alderson wrote: >> It is generally a good idea to re-form electrolytic capacitors in power >> supplies, and to bench check the power supplies (under some kind of >> load) before actually applying power to the whole unit. > > It is always a good idea to replace electrolytic capacitors in power supplies. > The rest of the advice is sound. > > Rich > > Rich Alderson > Vintage Computing Sr. Systems Engineer > Living Computer Museum > 2245 1st Avenue S > Seattle, WA 98134 > > mailto:ri...@livingcomputermuseum.org > > http://www.LivingComputerMuseum.org/ >
Re: PDP 11 gear finally moved
On 07/17/2015 11:53 AM, Mouse wrote: I do find this witch-hunt against capacitors to be curious, given how few I've found to have failed. I suspect a lot of it comes from audiophools who think this is the way to fix anything... Perhaps. But not all of it, certainly. I'm currently four for four fixing dead flatscreens by re-capping their power supplies; I imagine others have similar experiences. It's not a huge stretch to imagine that other power supplies may have similar issues; even if it turns out to not be the case, there is probably at least a little "can't hurt anything, right?" running around. /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTML mo...@rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B This is not surprising given the vintages of the machines. Modern machines using switching power supplies (15kHz+) must have capacitors with low ESR and high capacity to run properly. Older linear power supplies ran at 50/60hz and as such the capacitors had much less ripple current (and low frequency to boot) to deal with and the engineers typically over designed the values of capacitors to allow for some degradation. The machines you are playing with cost fortunes back in the day - they HAD to be reliable as possible. Modern caps run at or near their rated temperature (105C) last around 1,000 to 5,000 hours. The old linear supplies rarely heated the caps much over 40C and thus the caps would last decades...I put fans on our LCD monitors in our games and they last just fine. No fan? Expect a year or two at most before failure. John :-#)# -- John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames) www.flippers.com "Old pinballers never die, they just flip out"
Re: PDP 11 gear finally moved
I had to do some cap replacement on some older Motorola tube radios,I have some basic soldering skills. I was under the impression that the capacitors in computer equipment this big from this year would have been of better quality and it would not be an issue. I have someone scheduled to come out tonight after i get off work and get it out of the rack. On Fri, Jul 17, 2015 at 3:45 PM, Brent Hilpert wrote: > On 2015-Jul-17, at 11:42 AM, tony duell wrote: > >>> It is generally a good idea to re-form electrolytic capacitors in power > >>> supplies, and to bench check the power supplies (under some kind of > >>> load) before actually applying power to the whole unit. > >> > >> It is always a good idea to replace electrolytic capacitors in power > supplies. > > > > Could you, please, explain why? And how often should this be done? Every > > week, every month, every year, or what? > > > > FWIW, the number PSU elecrtrolytics I have replaced can be counted on > the fingers of > > one hand -- in unary. Well, perhaps both hands. But it's <1% of all the > PSU electrolytic > > capacitors I own. > > > > Only 2 cases spring to mind : > > > > The PSU in my 11/44 had a high ESR capacitor on the +36V rail (all other > caps in the machine > > were fine) > > > > I changed the 2 mains smoothing capacitors in my HP120 not because they > were electrically > > defective (they tested fine) but because one was bulging a little on top > and had it exploded it would > > have hit the neck of the CRT with all the problems that would be likely > to cause. > > > > I do find this witch-hunt against capacitors to be curious, given how > few I've found to have > > failed. I suspect a lot of it comes from audiophools who think this is > the way to fix anything... > > This is something Tony and I are quite in agreement on. > > Similar to Tony, (and as mentioned in discussion on this topic a couple of > months ago): in the solid-state category, of the many pieces of 1960s & 70s > and later equipment I have or have serviced, the vast majority are running > with their original capacitors. > > If you're dealing with a 1936 or 1952 tube radio, a knee-jerk "replace the > capacitors" is warranted. > If you're dealing with a 1970s computer, it isn't (IMHO). Esp. when > they're screw-terminal 'computer-grade' caps. > > My own perception of the concern is that it has been perpetuated over the > years from the vacuum tube / antique radio arena. The issue of capacitors > "drying out" dates from the days (1920s,early 30s) when electrolytics > actually were filled with an active liquid which actually did dry up. > "Dry electrolytics" were developed in the 1930s, and while early dry > electrolytics also warrant replacement, the chemistry and techniques have > seen a few improvements in the many intervening years, and solid-state > equipment is not placing the same stresses on caps as tube equipment. > > In other arenas it's a real issue, in a modern arena it is largely lore. > > The point of electrolytic caps is to form an oxide to be the dielectric, > formed (in part) out of the electrolyte, and while I'm no expert on the > chemistry, I will point out the oxidised state is 'the' or 'a' low energy > state, and hence relatively stable. Rust doesn't normally undo itself. > >
Re: PDP 11 gear finally moved
I was operating the panel when i first got it, now the numbers do not light up, panel is unresponsive, and run light stays lit.(just describing the behavior, i will not start it back up till I work on the power supply) On Fri, Jul 17, 2015 at 3:50 PM, devin davison wrote: > I had to do some cap replacement on some older Motorola tube radios,I have > some basic soldering skills. I was under the impression that the capacitors > in computer equipment this big from this year would have been of better > quality and it would not be an issue. > > I have someone scheduled to come out tonight after i get off work and get > it out of the rack. > > On Fri, Jul 17, 2015 at 3:45 PM, Brent Hilpert wrote: > >> On 2015-Jul-17, at 11:42 AM, tony duell wrote: >> >>> It is generally a good idea to re-form electrolytic capacitors in >> power >> >>> supplies, and to bench check the power supplies (under some kind of >> >>> load) before actually applying power to the whole unit. >> >> >> >> It is always a good idea to replace electrolytic capacitors in power >> supplies. >> > >> > Could you, please, explain why? And how often should this be done? Every >> > week, every month, every year, or what? >> > >> > FWIW, the number PSU elecrtrolytics I have replaced can be counted on >> the fingers of >> > one hand -- in unary. Well, perhaps both hands. But it's <1% of all the >> PSU electrolytic >> > capacitors I own. >> > >> > Only 2 cases spring to mind : >> > >> > The PSU in my 11/44 had a high ESR capacitor on the +36V rail (all >> other caps in the machine >> > were fine) >> > >> > I changed the 2 mains smoothing capacitors in my HP120 not because they >> were electrically >> > defective (they tested fine) but because one was bulging a little on >> top and had it exploded it would >> > have hit the neck of the CRT with all the problems that would be likely >> to cause. >> > >> > I do find this witch-hunt against capacitors to be curious, given how >> few I've found to have >> > failed. I suspect a lot of it comes from audiophools who think this is >> the way to fix anything... >> >> This is something Tony and I are quite in agreement on. >> >> Similar to Tony, (and as mentioned in discussion on this topic a couple >> of months ago): in the solid-state category, of the many pieces of 1960s & >> 70s and later equipment I have or have serviced, the vast majority are >> running with their original capacitors. >> >> If you're dealing with a 1936 or 1952 tube radio, a knee-jerk "replace >> the capacitors" is warranted. >> If you're dealing with a 1970s computer, it isn't (IMHO). Esp. when >> they're screw-terminal 'computer-grade' caps. >> >> My own perception of the concern is that it has been perpetuated over the >> years from the vacuum tube / antique radio arena. The issue of capacitors >> "drying out" dates from the days (1920s,early 30s) when electrolytics >> actually were filled with an active liquid which actually did dry up. >> "Dry electrolytics" were developed in the 1930s, and while early dry >> electrolytics also warrant replacement, the chemistry and techniques have >> seen a few improvements in the many intervening years, and solid-state >> equipment is not placing the same stresses on caps as tube equipment. >> >> In other arenas it's a real issue, in a modern arena it is largely lore. >> >> The point of electrolytic caps is to form an oxide to be the dielectric, >> formed (in part) out of the electrolyte, and while I'm no expert on the >> chemistry, I will point out the oxidised state is 'the' or 'a' low energy >> state, and hence relatively stable. Rust doesn't normally undo itself. >> >> >
Re: PDP 11 gear finally moved
Thank you for the detailed information. I need to figure out how im going to get it out of the rack and moved to a place where i can test it over the next couple days where it will not be in the way. Ill find some way to do a dummy load and do an extended test to be sure the supply is working properly. All fingers crossed, god it better not have damaged any of the boards, i do not know where i would get replacements.It took years for me to get the machine, who knows how long it would take to find a specific board that is bad. I did buy an oscillicope and a logic analyzer well in advance in preparation for getting this machine, however short of pressing the power button no clue how to use them or basic troubleshooting procedures. Guess i just have to learn by doing On Fri, Jul 17, 2015 at 3:23 PM, tony duell wrote: > > > When I repaired my VT100s I had to replace all the electrolytic caps on > the > > monitor control board to cure the screen wobble. Before doing so I had > > reformed them all and I had tested them all for ESR and they had all > tested > > fine so I was unable to determine which of them was the bad one. Perhaps > > there is other more professional test equipment I could use that would > have > > helped, I don't know. I did keep all the original caps though > (somewhere). > > Are you saying that if you put any of the original capacitors back > (leaving new > ones in all other locations) you get screen wobble. If so, I am not sure I > believe you. It's been some years since I repaired a VT100, but from what I > remember there are plenty of capacitors that simply could not cause > screen wobble no matter what they were doing. > > Or did you recap the board and find that it then worked. In which case (a) > perhaps only one of the capacitors was faulty or (b) it was actually a dry > joint. > > -tony >
RE: PDP 11 gear finally moved
> -Original Message- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of tony duell > Sent: 17 July 2015 20:23 > To: General Discussion: On-Topic and Off-Topic Posts > Subject: RE: PDP 11 gear finally moved > > > > When I repaired my VT100s I had to replace all the electrolytic caps > > on the monitor control board to cure the screen wobble. Before doing > > so I had reformed them all and I had tested them all for ESR and they > > had all tested fine so I was unable to determine which of them was the > > bad one. Perhaps there is other more professional test equipment I > > could use that would have helped, I don't know. I did keep all the original caps > though (somewhere). > > Are you saying that if you put any of the original capacitors back (leaving new > ones in all other locations) you get screen wobble. If so, I am not sure I believe > you. It's been some years since I repaired a VT100, but from what I remember > there are plenty of capacitors that simply could not cause screen wobble no > matter what they were doing. > > Or did you recap the board and find that it then worked. In which case (a) > perhaps only one of the capacitors was faulty or (b) it was actually a dry joint. > > -tony > = I am saying that I recapped the entire board, so one or more of them must have been bad. I agree it could have been a dry joint, but I am not going to put them all back just to check :-) This happened on *two* of these boards, so either I had two dry joints, or two bad caps. Regards Rob
Re: PDP 11 gear finally moved
On 2015-Jul-17, at 11:42 AM, tony duell wrote: >>> It is generally a good idea to re-form electrolytic capacitors in power >>> supplies, and to bench check the power supplies (under some kind of >>> load) before actually applying power to the whole unit. >> >> It is always a good idea to replace electrolytic capacitors in power >> supplies. > > Could you, please, explain why? And how often should this be done? Every > week, every month, every year, or what? > > FWIW, the number PSU elecrtrolytics I have replaced can be counted on the > fingers of > one hand -- in unary. Well, perhaps both hands. But it's <1% of all the PSU > electrolytic > capacitors I own. > > Only 2 cases spring to mind : > > The PSU in my 11/44 had a high ESR capacitor on the +36V rail (all other caps > in the machine > were fine) > > I changed the 2 mains smoothing capacitors in my HP120 not because they were > electrically > defective (they tested fine) but because one was bulging a little on top and > had it exploded it would > have hit the neck of the CRT with all the problems that would be likely to > cause. > > I do find this witch-hunt against capacitors to be curious, given how few > I've found to have > failed. I suspect a lot of it comes from audiophools who think this is the > way to fix anything... This is something Tony and I are quite in agreement on. Similar to Tony, (and as mentioned in discussion on this topic a couple of months ago): in the solid-state category, of the many pieces of 1960s & 70s and later equipment I have or have serviced, the vast majority are running with their original capacitors. If you're dealing with a 1936 or 1952 tube radio, a knee-jerk "replace the capacitors" is warranted. If you're dealing with a 1970s computer, it isn't (IMHO). Esp. when they're screw-terminal 'computer-grade' caps. My own perception of the concern is that it has been perpetuated over the years from the vacuum tube / antique radio arena. The issue of capacitors "drying out" dates from the days (1920s,early 30s) when electrolytics actually were filled with an active liquid which actually did dry up. "Dry electrolytics" were developed in the 1930s, and while early dry electrolytics also warrant replacement, the chemistry and techniques have seen a few improvements in the many intervening years, and solid-state equipment is not placing the same stresses on caps as tube equipment. In other arenas it's a real issue, in a modern arena it is largely lore. The point of electrolytic caps is to form an oxide to be the dielectric, formed (in part) out of the electrolyte, and while I'm no expert on the chemistry, I will point out the oxidised state is 'the' or 'a' low energy state, and hence relatively stable. Rust doesn't normally undo itself.
RE: PDP 11 gear finally moved
> When I repaired my VT100s I had to replace all the electrolytic caps on the > monitor control board to cure the screen wobble. Before doing so I had > reformed them all and I had tested them all for ESR and they had all tested > fine so I was unable to determine which of them was the bad one. Perhaps > there is other more professional test equipment I could use that would have > helped, I don't know. I did keep all the original caps though (somewhere). Are you saying that if you put any of the original capacitors back (leaving new ones in all other locations) you get screen wobble. If so, I am not sure I believe you. It's been some years since I repaired a VT100, but from what I remember there are plenty of capacitors that simply could not cause screen wobble no matter what they were doing. Or did you recap the board and find that it then worked. In which case (a) perhaps only one of the capacitors was faulty or (b) it was actually a dry joint. -tony
RE: PDP 11 gear finally moved
> -Original Message- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of tony duell > Sent: 17 July 2015 19:56 > To: General Discussion: On-Topic and Off-Topic Posts > Subject: RE: PDP 11 gear finally moved > > > > > Perhaps. But not all of it, certainly. I'm currently four for four > > fixing dead flatscreens by re-capping their power supplies; I imagine > > others have similar experiences. It's not a huge stretch to imagine > > This could be taken to show that modern capacitors are not reliable, and given > that there are plenty of 40-year-old ones still in use in various classic > computers here it would be better to leave them as-is > > More seriously, a lot of modern consumer stuff seems to have marginally-rated > capacitors (and the use of 85 degree ones doesn't help). Possibly on those it is a > good idea to replace them. But the ones in PDP11s were good quality at the > start and were over-spec'd in general. > > > that other power supplies may have similar issues; even if it turns > > out to not be the case, there is probably at least a little "can't > > hurt anything, right?" running around. > > Ah but it can hurt. Damage to the PCB (unlikely, sure), the new part might be > faulty and thus introduce more faults, you might make an error fitting it, and so > on. I prefer to only replace that which needs replacing. > > -tony > = When I repaired my VT100s I had to replace all the electrolytic caps on the monitor control board to cure the screen wobble. Before doing so I had reformed them all and I had tested them all for ESR and they had all tested fine so I was unable to determine which of them was the bad one. Perhaps there is other more professional test equipment I could use that would have helped, I don't know. I did keep all the original caps though (somewhere). Regards Rob
RE: PDP 11 gear finally moved
> > Perhaps. But not all of it, certainly. I'm currently four for four > fixing dead flatscreens by re-capping their power supplies; I imagine > others have similar experiences. It's not a huge stretch to imagine This could be taken to show that modern capacitors are not reliable, and given that there are plenty of 40-year-old ones still in use in various classic computers here it would be better to leave them as-is More seriously, a lot of modern consumer stuff seems to have marginally-rated capacitors (and the use of 85 degree ones doesn't help). Possibly on those it is a good idea to replace them. But the ones in PDP11s were good quality at the start and were over-spec'd in general. > that other power supplies may have similar issues; even if it turns out > to not be the case, there is probably at least a little "can't hurt > anything, right?" running around. Ah but it can hurt. Damage to the PCB (unlikely, sure), the new part might be faulty and thus introduce more faults, you might make an error fitting it, and so on. I prefer to only replace that which needs replacing. -tony
Re: PDP 11 gear finally moved
some are good some are bad. http://www.badcaps.net/ here is all the info you ever need on today's bad caps not so much on yesteryears bad caps On 7/17/2015 11:53 AM, Mouse wrote: >> I do find this witch-hunt against capacitors to be curious, given how >> few I've found to have failed. I suspect a lot of it comes from >> audiophools who think this is the way to fix anything... > Perhaps. But not all of it, certainly. I'm currently four for four > fixing dead flatscreens by re-capping their power supplies; I imagine > others have similar experiences. It's not a huge stretch to imagine > that other power supplies may have similar issues; even if it turns out > to not be the case, there is probably at least a little "can't hurt > anything, right?" running around. > > /~\ The ASCII Mouse > \ / Ribbon Campaign > X Against HTML mo...@rodents-montreal.org > / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B > -- The contents of this e-mail and any attachments are intended solely for the use of the named addressee(s) and may contain confidential and/or privileged information. Any unauthorized use, copying, disclosure, or distribution of the contents of this e-mail is strictly prohibited by the sender and may be unlawful. If you are not the intended recipient, please notify the sender immediately and delete this e-mail.
Re: PDP 11 gear finally moved
I suspect part of the "swap'em ALL out" mentality comes from the 90's when some botched industrial espionage had some of the bottom-tier cap manufacturers using a dodgy electrolytic formula for their caps. These caps would have a frequent failure rate.. While not an issue for pre-90's electronics, it has fostered the mentality of full replacement for 'newer' electronics i.e. arcade/pinball machines Todd Killingsworth On Fri, Jul 17, 2015 at 2:42 PM, tony duell wrote: > > > > > It is generally a good idea to re-form electrolytic capacitors in power > > > supplies, and to bench check the power supplies (under some kind of > > > load) before actually applying power to the whole unit. > > > > It is always a good idea to replace electrolytic capacitors in power > supplies. > > Could you, please, explain why? And how often should this be done? Every > week, every month, every year, or what? > > FWIW, the number PSU elecrtrolytics I have replaced can be counted on the > fingers of > one hand -- in unary. Well, perhaps both hands. But it's <1% of all the > PSU electrolytic > capacitors I own. > > Only 2 cases spring to mind : > > The PSU in my 11/44 had a high ESR capacitor on the +36V rail (all other > caps in the machine > were fine) > > I changed the 2 mains smoothing capacitors in my HP120 not because they > were electrically > defective (they tested fine) but because one was bulging a little on top > and had it exploded it would > have hit the neck of the CRT with all the problems that would be likely to > cause. > > I do find this witch-hunt against capacitors to be curious, given how few > I've found to have > failed. I suspect a lot of it comes from audiophools who think this is the > way to fix anything... > > -tony >
Re: PDP 11 gear finally moved
> I do find this witch-hunt against capacitors to be curious, given how > few I've found to have failed. I suspect a lot of it comes from > audiophools who think this is the way to fix anything... Perhaps. But not all of it, certainly. I'm currently four for four fixing dead flatscreens by re-capping their power supplies; I imagine others have similar experiences. It's not a huge stretch to imagine that other power supplies may have similar issues; even if it turns out to not be the case, there is probably at least a little "can't hurt anything, right?" running around. /~\ The ASCII Mouse \ / Ribbon Campaign X Against HTMLmo...@rodents-montreal.org / \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
RE: PDP 11 gear finally moved
> > > It is generally a good idea to re-form electrolytic capacitors in power > > supplies, and to bench check the power supplies (under some kind of > > load) before actually applying power to the whole unit. > > It is always a good idea to replace electrolytic capacitors in power supplies. Could you, please, explain why? And how often should this be done? Every week, every month, every year, or what? FWIW, the number PSU elecrtrolytics I have replaced can be counted on the fingers of one hand -- in unary. Well, perhaps both hands. But it's <1% of all the PSU electrolytic capacitors I own. Only 2 cases spring to mind : The PSU in my 11/44 had a high ESR capacitor on the +36V rail (all other caps in the machine were fine) I changed the 2 mains smoothing capacitors in my HP120 not because they were electrically defective (they tested fine) but because one was bulging a little on top and had it exploded it would have hit the neck of the CRT with all the problems that would be likely to cause. I do find this witch-hunt against capacitors to be curious, given how few I've found to have failed. I suspect a lot of it comes from audiophools who think this is the way to fix anything... -tony
RE: PDP 11 gear finally moved
> > I was trying to enter a short program at the front panel and there was a > clicking sound followed by a burning smell. I cut the power, the front > panel is unresponsive now, so I'm going to need to look over the power Did you see anything on the panel when it died (was the numeric display still alight) ? You had better hope that the +5V line didn't go high and cook all the ICs in the machine. DEC PSUs of that vintage do have crowbar circuits though. > supply for starters. He did include a second empty PDP 11/34 chassis, > perhaps the power supply in that one is in better condition. The PSU in this machine is relatively repairer-friendly. There is a big mains transformer in the centre of the PSU chassis (at the back of the CPU). It takes mains in (there are 2 primary windings, each 115V, they are connected in parallel for US mains and series for European mains). It has several secondaries, each of about 20V-30V AC Under the mains transformer is a little unit that contains the mains switching relay and control circuits, and a simple linear PSU for the +15V rail. I think the LTC (line time clock), ACLO and DCLO (power failure signals) come from that too. The main supply rails (+5V and -15V) come from 'bricks' that fit either side of the transformer. These are swtiching regulators that take in the 20V or so from the transformer and bring it down to the desired voltage. Although they are switchers, the maximum voltage inside is just the rectified input (say about 40V DC) and is thus a lot nicer to work on than a mains-operated switcher. The bricks are based round the 723 IC along with some transistors, an inductor, flyback diode, capacitors, etc. What I would do is disconnect the logic backplane power (at the distribution connectors under the PSU) then take the PSU covers off, take out the bottom 2 screws each side and loosen the top on so the PSU can hinge away from the CPU and remove the power bricks. Power up the transformer on its own (maybe with a series light bub) and check that is OK. Then try to debug the bricks. If you have a bench PSU with current limiting run them (one at a time) off that (they will happing run from a DC input) and see what happens. The +5V brick just needs the 20V-30V input, the -15V one _also_ needs a +15V supply. -tony
Re: PDP 11 gear finally moved
It is generally a good idea to re-form electrolytic capacitors in power supplies, and to bench check the power supplies (under some kind of load) before actually applying power to the whole unit. JRJ On 7/17/2015 11:49 AM, devin davison wrote: > Devin here, I had asked for advice on how to move a PDP 11 as well as how > to lock the heads on the RL Drives. It was quite a move. Ive never driven > in a large city before, dealing with traffic was more trouble than it was > to move and load up the equipment. Anyhow, i put a few images of what I got > up on a postimage gallery, which can be viewed here : > > http://postimg.org/gallery/1xuwq2s6y/ > > It was at least working for a hour or so > I was trying to enter a short program at the front panel and there was a > clicking sound followed by a burning smell. I cut the power, the front > panel is unresponsive now, so I'm going to need to look over the power > supply for starters. He did include a second empty PDP 11/34 chassis, > perhaps the power supply in that one is in better condition. > > --Devin >
RE: PDP 11 gear finally moved
> It is generally a good idea to re-form electrolytic capacitors in power > supplies, and to bench check the power supplies (under some kind of > load) before actually applying power to the whole unit. I am not sure either would have done much good here. The OP said it ran OK for an hour or so, when you test a PSU on dummy load you typically do it for a lot less time than that, Incidentally, DEC PSUs of this type run fine with no load in my experience Also I have found the capacitors in these units to be very reliable. They can fail, of course, but virtually all the DEC bricks I have are on their original capacitors. I think I've replaced more chopper transistors than capacitors in these. -tony
RE: PDP 11 gear finally moved
> It is generally a good idea to re-form electrolytic capacitors in power > supplies, and to bench check the power supplies (under some kind of > load) before actually applying power to the whole unit. It is always a good idea to replace electrolytic capacitors in power supplies. The rest of the advice is sound. Rich Rich Alderson Vintage Computing Sr. Systems Engineer Living Computer Museum 2245 1st Avenue S Seattle, WA 98134 mailto:ri...@livingcomputermuseum.org http://www.LivingComputerMuseum.org/
