Re: DECstation 220 - Out of Ideas?
On 25/06/2017 11:46, Rob Jarratt via cctalk wrote: I have done a bit more tracing of components and have come across a possibly anomaly. The signal that won't go low enough goes to the input (pin 2) of a 74LS125 buffer. OK, for SOIC parts, here's my technique. (I've had to replace quite a few of them.) First, use solder wick to remove solder from one side of the chip. Then, use an X-acto knife under a pin, and while heating the solder pad, lever the knife to lift each pin outward and up, free from the solder. Work your way down one side of the chip until all leads are free of solder. Now, take the X-acto blade and score all the other leads right near the plastic body. Just a couple swipes of the blade is enough. Now, tilt the body up, press down, and repeat a couple times and the body will break off of the leads. Now, remove remaining leads by just sweeping them off the board, and clean up the pads with solder wick. Takes maybe 2 minutes, and almost never damages the board. Jon
Re: DB11-A Bus Repeater Engineering Drawings
Well, at least it was DEC who messed up and not me (this time). Noel, thanks for scanning. Al, thanks for figuring it out. Paul On Sat, Jun 24, 2017 at 11:50 AM, Al Kossow via cctalk < cctalk@classiccmp.org> wrote: > They screwed up when they made the maint prints, it's missing from ours as > well > > I will see if it showed up in the individual module schematic collections, > though > that will be much more difficult to go through. I scanned binders full of > them, but > they aren't sorted. > > > On 6/24/17 9:21 AM, Al Kossow via cctalk wrote: > > > > > > On 6/24/17 9:14 AM, Noel Chiappa via cctalk wrote: > > > >> Does anyone else have a set of these prints? > > > > > > http://www.computerhistory.org/collections/catalog/102753063 > > > > i'll try to get to it today > > > > > >
RE: DECstation 220 - Out of Ideas?
> -Original Message- > From: Dave Wade [mailto:dave.g4...@gmail.com] > Sent: 25 June 2017 20:26 > To: r...@jarratt.me.uk; 'Rob Jarratt' ; 'General > Discussion: On-Topic and Off-Topic Posts' > Subject: RE: DECstation 220 - Out of Ideas? > > Rob, > I have a cheap hot air re-work station that you are welcome to borrow. You > might need to order a nozzle as I do,t have many Dave > > That is very kind Dave. I think I might first try some Chip Quik, but it would be interesting to have a go with a hot air rework station at some point. Regards Rob
Re: TV Typewriter project nearing completion
wow impressive work Brad! Thanks for blogging about it, it's fun to watch you progress. Ever consider selling some of the PCB boards, and coming up with a BOM list, so we can recreate some too?
Re: DECstation 220 - Out of Ideas?
Heheh, that's a cool idea. I use a post-it note, sliding a non-sticky side under the pins (from the rear of said pins) as I drag the iron across all the pins. =] On Sun, Jun 25, 2017 at 11:27 AM Pete Turnbull via cctalk < cctalk@classiccmp.org> wrote: > On 25/06/2017 11:46, Rob Jarratt via cctalk wrote: > > > I have done a bit more tracing of components and have come across a > > possibly anomaly. The signal that won't go low enough goes to the > > input (pin 2) of a 74LS125 buffer. > > As soon as I saw "74LS125" I thought, "Oh, yes, another one". That's a > fairly early design tri-state buffer, and in my experience they're not > very robust. We used to replace lots of those, though admittedly I'm > referring to the DIL version. Worth checking it out. > > If you can't desolder all the SMD pins, try this trick: for each side, > thread a piece of enamelled copper wire under the chip near the pins. > Tie or wrap one one to some nearby component and hold the other end in > your hand. Starting at the end with the wire you're holding, heat each > pin with your soldering iron, and drag the wire under it, thereby > breaking its contact with the board. > > Failing that, apply a tiny amount of flux to the pins, and heat it up > with a hot air gun, preferably a temperature-controlled one, and lift it > off with forceps (or flip it over with a small screwdriver). > > -- > Pete > Pete Turnbull > -- -- Anders Nelson +1 (517) 775-6129 www.erogear.com
RE: DECstation 220 - Out of Ideas?
Rob, I have a cheap hot air re-work station that you are welcome to borrow. You might need to order a nozzle as I do,t have many Dave > -Original Message- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Rob Jarratt > via cctalk > Sent: 25 June 2017 11:47 > To: 'General Discussion: On-Topic and Off-Topic Posts' > ; 'Ian S. King' > Subject: RE: DECstation 220 - Out of Ideas? > > > > > Thanks Ian. Unfortunately I don't know of any schematics. I suspect > > you are right about it being a wire-OR because the documentation for > > the P82C206 says its output is tri-state. As everything is soldered on > > rather than socketed (except the ROMs) I am not sure I can measure any > > currents, nor can I think of a way to check if the other chip > > (Olivetti GA099-B) is trying to drive the output the other way :-(. I > > will check the resistance between the outputs of the P82C206 and the ROM > inputs and of the Vss pins. > > > > > I have done a bit more tracing of components and have come across a > possibly anomaly. The signal that won't go low enough goes to the input (pin > 2) of a 74LS125 buffer. The resistance across the input and output (pins 2-3) > is > a few Kohm. Other input-output resistances on this chip are much higher. > The same goes for Vcc to the input, the resistance is much lower than Vcc to > other inputs. It could be that the 74LS125 is faulty, or something else on > that > line has a low resistance path to Vcc, either way it would seem to be a > possible reason for the signal never to go low enough. > > I think I am going to have to get myself a cheap hot air rework station to > allow > me to remove the 74LS125 (it is surface mounted) so I can check it out of > circuit. > > However, I was looking at this machine with a view to passing it on anyway. Is > there anyone in the UK who would be interested in it (unrepaired)? It would > be just for the cost of post and packing, or you can collect from the > Manchester area. > > Regards > > Rob
Re: DECstation 220 - Out of Ideas?
On 06/25/2017 11:41 AM, Rob Jarratt wrote: > Thanks Chuck, I had seen some mention of Chip Quik. You say soldering a new > part is straightforward, but I am not clear how that works, is the solder > left behind on the pads so you just heat the pins? As mentioned, I use the toothbrush to scrub the pads "clean" of any leftover alloy+solder mixture, then place the part, tack the corner leads into place with a bit of solder, then flow solder across all the leads and clean up with a bit of solder wick. I've done 0.5mm QFP parts this way without issue. Some use a bit of Blu-Tack under the package to hold it in place, but I've never found that to be necessary. There are several YT videos on this technique, including, I believe, Dave's EEVBlog. It's easier than it looks. --Chuck
RE: DECstation 220 - Out of Ideas?
> When replacing components on an SMD board, I prefer to use a low-temp > fusible alloy such as "Chip Quik": > > http://www.chipquik.com/store/ > > A nice kit, but really, any low temp fusible alloy will work. I use > Cerrobend as a > powder, packed around the IC. > > http://www.csalloys.com/specifications.html > > I heat the board from the underside with a PAR38 halogen spotlight, which > raises the temperature to around the point where it becomes uncomfortable to > the touch. > > The part then just slides off; the IC pads (and the IC itself if you want to > re-use > it) can be cleaned with a toothbrush and the continued application of light > heating. > > All the parts around the IC are unaffected and soldering a new part is > straightforward. > Thanks Chuck, I had seen some mention of Chip Quik. You say soldering a new part is straightforward, but I am not clear how that works, is the solder left behind on the pads so you just heat the pins? Regards Rob
Re: DECstation 220 - Out of Ideas?
On 06/25/2017 09:24 AM, Rob Jarratt via cctalk wrote: > Thanks Pete, so there is enough of a chance that I have found the > culprit to make it worth the effort of desoldering it. > > I have been wondering for a while about getting a hot air rework > station. There are lots of cheap Chinese ones on Ebay. Given my > likely light use it feels worth getting one at this point. Anyone > tried one of these: > http://www.ebay.co.uk/itm/Genuine-WEP-640W-Hot-Air-Gun-Soldering-Rework-Station-Temp-Control-Digital-/112453738508? > At that price it feels worth the gamble. When replacing components on an SMD board, I prefer to use a low-temp fusible alloy such as "Chip Quik": http://www.chipquik.com/store/ A nice kit, but really, any low temp fusible alloy will work. I use Cerrobend as a powder, packed around the IC. http://www.csalloys.com/specifications.html I heat the board from the underside with a PAR38 halogen spotlight, which raises the temperature to around the point where it becomes uncomfortable to the touch. The part then just slides off; the IC pads (and the IC itself if you want to re-use it) can be cleaned with a toothbrush and the continued application of light heating. All the parts around the IC are unaffected and soldering a new part is straightforward. FWIW, Chuck
Re: DB11-A Bus Repeater Engineering Drawings
> From: Al Kossow Hey, thanks for all the effort to help... > which has the schematic > they have been there for over three years $@#&($^@(*$&^! That's what I get for trusting Google; I tried searching for '"DB11-A" prints' and '"DB11-A" drawings' and got nothing ... except for a Manx listing: http://manx-docs.org/details.php/1,9242 which said they weren't online. $@*(&$^@*!!! (Note: I am _not_ criticizing Manx, which is an incredibly valuable resource - it's just that that entry did dissuade me from further searching...) Well, lesson for the future: check Bitsavers manually, first... Noel
RE: DECstation 220 - Out of Ideas?
> -Original Message- > From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Pete > Turnbull via cctalk > Sent: 25 June 2017 16:12 > To: cctalk@classiccmp.org > Subject: Re: DECstation 220 - Out of Ideas? > > As soon as I saw "74LS125" I thought, "Oh, yes, another one". That's a fairly > early design tri-state buffer, and in my experience they're not very robust. > We > used to replace lots of those, though admittedly I'm referring to the DIL > version. Worth checking it out. > > If you can't desolder all the SMD pins, try this trick: for each side, thread > a > piece of enamelled copper wire under the chip near the pins. > Tie or wrap one one to some nearby component and hold the other end in your > hand. Starting at the end with the wire you're holding, heat each pin with > your > soldering iron, and drag the wire under it, thereby breaking its contact with > the > board. > > Failing that, apply a tiny amount of flux to the pins, and heat it up with a > hot air > gun, preferably a temperature-controlled one, and lift it off with forceps > (or flip > it over with a small screwdriver). > Thanks Pete, so there is enough of a chance that I have found the culprit to make it worth the effort of desoldering it. I have been wondering for a while about getting a hot air rework station. There are lots of cheap Chinese ones on Ebay. Given my likely light use it feels worth getting one at this point. Anyone tried one of these: http://www.ebay.co.uk/itm/Genuine-WEP-640W-Hot-Air-Gun-Soldering-Rework-Station-Temp-Control-Digital-/112453738508? At that price it feels worth the gamble. Regards Rob
Re: DECstation 220 - Out of Ideas?
On 25/06/2017 11:46, Rob Jarratt via cctalk wrote: I have done a bit more tracing of components and have come across a possibly anomaly. The signal that won't go low enough goes to the input (pin 2) of a 74LS125 buffer. As soon as I saw "74LS125" I thought, "Oh, yes, another one". That's a fairly early design tri-state buffer, and in my experience they're not very robust. We used to replace lots of those, though admittedly I'm referring to the DIL version. Worth checking it out. If you can't desolder all the SMD pins, try this trick: for each side, thread a piece of enamelled copper wire under the chip near the pins. Tie or wrap one one to some nearby component and hold the other end in your hand. Starting at the end with the wire you're holding, heat each pin with your soldering iron, and drag the wire under it, thereby breaking its contact with the board. Failing that, apply a tiny amount of flux to the pins, and heat it up with a hot air gun, preferably a temperature-controlled one, and lift it off with forceps (or flip it over with a small screwdriver). -- Pete Pete Turnbull
Re: Free HP 9836 in Santa Cruz, CA
On 2017-06-23 14:55, Connor Krukosky via cctalk wrote: I am in no way affiliated and wish it wasn't on the other side of the country so I could get it! https://sfbay.craigslist.org/scz/sys/6188389886.html "I have a single monochrome HP 9836 computer with two monitors and three printers left. All completely untested, but free!" Did anybody picked them up? I would love to have the main units (don't care about the monitors), which don't work. so anybody could arrange shipping if they are still available? Thanks!
RE: DECstation 220 - Out of Ideas?
> Thanks Ian. Unfortunately I don't know of any schematics. I suspect you are > right about it being a wire-OR because the documentation for the P82C206 says > its output is tri-state. As everything is soldered on rather than socketed > (except > the ROMs) I am not sure I can measure any currents, nor can I think of a way > to > check if the other chip (Olivetti GA099-B) is trying to drive the output the > other > way :-(. I will check the resistance between the outputs of the P82C206 and > the > ROM inputs and of the Vss pins. > I have done a bit more tracing of components and have come across a possibly anomaly. The signal that won't go low enough goes to the input (pin 2) of a 74LS125 buffer. The resistance across the input and output (pins 2-3) is a few Kohm. Other input-output resistances on this chip are much higher. The same goes for Vcc to the input, the resistance is much lower than Vcc to other inputs. It could be that the 74LS125 is faulty, or something else on that line has a low resistance path to Vcc, either way it would seem to be a possible reason for the signal never to go low enough. I think I am going to have to get myself a cheap hot air rework station to allow me to remove the 74LS125 (it is surface mounted) so I can check it out of circuit. However, I was looking at this machine with a view to passing it on anyway. Is there anyone in the UK who would be interested in it (unrepaired)? It would be just for the cost of post and packing, or you can collect from the Manchester area. Regards Rob
RE: DECstation 220 - Out of Ideas?
> -Original Message- > From: Ian S. King [mailto:isk...@uw.edu] > Sent: 25 June 2017 01:07 > To: r...@jarratt.me.uk; Rob Jarratt ; General > Discussion: On-Topic and Off-Topic Posts > Subject: Re: DECstation 220 - Out of Ideas? > > Rob > I don't recall from this thread - do you have prints? I'd try to divine > whether > this is a wire-OR bus (likely). If so, I'd suspect the P82C206. It may not > be toast > itself - be sure it has sufficient power to drive the OC transistor that's > bringing > down the bus, and that its connection to that bus doesn't have excessive > resistance, and that its ground (earth) connection is also low-resistance. A > long > shot: it could be something else on that bus that's sourcing rather than > sinking, > but the scenario seems unlikely. > > I'd agree that it's probably not the ROMs, from the symptoms you're describing > - unless, again, one of them has an internal short/leak to rail on its > read-enable > pin. A thought: can you measure the current and its direction on the P82C206 > pin? > > That's my troubleshooting thinking given that I don't have it in front of me. > :-) I > hope this is helpful -- Ian > > > Thanks Ian. Unfortunately I don't know of any schematics. I suspect you are right about it being a wire-OR because the documentation for the P82C206 says its output is tri-state. As everything is soldered on rather than socketed (except the ROMs) I am not sure I can measure any currents, nor can I think of a way to check if the other chip (Olivetti GA099-B) is trying to drive the output the other way :-(. I will check the resistance between the outputs of the P82C206 and the ROM inputs and of the Vss pins. Regards Rob
Re: Free HP 9836 in Santa Cruz, CA
Good eye! That's Bob indeed. Marc From: cctalk on behalf of "cctalk@classiccmp.org" Reply-To: dwight , "cctalk@classiccmp.org" Date: Friday, June 23, 2017 at 2:45 PM To: Connor Krukosky , "cctalk@classiccmp.org" Subject: Re: Free HP 9836 in Santa Cruz, CA Sounds like Bob Rosenbloom. Dwight From: cctalk on behalf of Connor Krukosky via cctalk Sent: Friday, June 23, 2017 5:55:53 AM To: General Discussion: On-Topic and Off-Topic Posts Subject: Free HP 9836 in Santa Cruz, CA I am in no way affiliated and wish it wasn't on the other side of the country so I could get it! https://sfbay.craigslist.org/scz/sys/6188389886.html "I have a single monochrome HP 9836 computer with two monitors and three printers left. All completely untested, but free!" Hope someone can save these, it looks like they might be owned by a collector as it is? Last photo has TWO ASR33s in the corners of the photo! -Connor K
