Re: [time-nuts] Anyone familiar with SR-620 repair?
MW or LW IR cameras are not exactly home shop stuff Peter. -John == I had a HP 3326 which had a power supply in foldback. All the modules are inaccessible unless you have a rather rare set of extenders anyway. The voltmeter method quickly led me to the board and a bench supply and meter again to the shorted cap. Very easy. Other times I've borrowed the FLIR camera from work, also taught the new EEs that trick as well. It is a true lifesaver on dense surface mount boards. I haven't tried the liquid crystal sheet but it seems like an interesting idea so long as everything is about the same height. Peter On Mar 23, 2012, at 11:53 PM, li...@lazygranch.com wrote: Prior to emission or IR microscope technology, liquid crystals was how you found hotspots on ICs. I've done this with a goop that you dispense with a syringe. One trick to make this more sensitive is you bring a soldering iron close to the liquid crystals. Not so close as to cause a change, but you get them closer to the phase change point. -Original Message- From: Skip Withrow skip.with...@gmail.com Sender: time-nuts-boun...@febo.com Date: Fri, 23 Mar 2012 21:07:45 To: time-nuts@febo.com Reply-To: swith...@alum.mit.edu, Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] Anyone familiar with SR-620 repair? You don't need expensive test equipment to find this kind of problem. What I use is a sheet of liquid crystal film with a transition temperature just slightly above your room temperature. Just lay it on the circuit board and you can find where the power is being dissipated (even if pretty small) by watching the colors change. I think Omega Engineering sells a 8.5 x 11 sheet for about $18 if memory serves me. I have used this trick many times and it works great to find shorted (bypass) caps. No disconnecting anything, no milliohm meters, no 4 or 5 digit voltmeters. Regards, Skip Withrow ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Nope. The cap was cool because the thing was shorted and had no voltage across it. Power is V * I. As I said before, either an open or a short circuited component dissipates no power. The defective component is NOT always the hot one. A hot component is only a pointer to the fault, not necessarily the problem itself. This is especially true of fuses. Always ask Why did the fuse blow?? -John = I just tracked down a shorted tantalum in a Tektronix DM501 multimeter. It was on the output of the floating -12 volt supply bridge rectifier before the regulator. The current level was so low that it never heated up although I burned two fingers on the push-pull output transistors for the floating supply. The regulator is on a separate module but the supply was still shorted when I pulled it and the bad tantalum was the only part left. I have not seen a shorted tantalum before where it could not be surge current related until now. On Sat, 24 Mar 2012 00:08:12 -0400, Peter Gottlieb n...@verizon.net wrote: I had a HP 3326 which had a power supply in foldback. All the modules are inaccessible unless you have a rather rare set of extenders anyway. The voltmeter method quickly led me to the board and a bench supply and meter again to the shorted cap. Very easy. Other times I've borrowed the FLIR camera from work, also taught the new EEs that trick as well. It is a true lifesaver on dense surface mount boards. I haven't tried the liquid crystal sheet but it seems like an interesting idea so long as everything is about the same height. Peter On Mar 23, 2012, at 11:53 PM, li...@lazygranch.com wrote: Prior to emission or IR microscope technology, liquid crystals was how you found hotspots on ICs. I've done this with a goop that you dispense with a syringe. One trick to make this more sensitive is you bring a soldering iron close to the liquid crystals. Not so close as to cause a change, but you get them closer to the phase change point. -Original Message- From: Skip Withrow skip.with...@gmail.com Sender: time-nuts-boun...@febo.com Date: Fri, 23 Mar 2012 21:07:45 To: time-nuts@febo.com Reply-To: swith...@alum.mit.edu, Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] Anyone familiar with SR-620 repair? You don't need expensive test equipment to find this kind of problem. What I use is a sheet of liquid crystal film with a transition temperature just slightly above your room temperature. Just lay it on the circuit board and you can find where the power is being dissipated (even if pretty small) by watching the colors change. I think Omega Engineering sells a 8.5 x 11 sheet for about $18 if memory serves me. I have used this trick many times and it works great to find shorted (bypass) caps. No disconnecting anything, no milliohm meters, no 4 or 5 digit voltmeters. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
The capacitor was cool in this case because the floating supply was current limited do to the design so the power dissipation was limited. The transistors driving the isolation transformer were beta limited and the output current after the transformer was on the order of 200 milliamps. Had the capacitor been on the input side, the short circuit current would have been an order of magnitude or two higher and I expect it would have been hot or even caught on fire. The only thing that made it easy to find was that removing the post regulator as a module left only that one capacitor in the circuit. I actually have a far IR camera but did not get to breaking it out for this project. I did manage to burn two Mark I Fingers though on the metal transistor cans. The DM501 I fixed supports a simple delta Vbe temperature probe so at some point I think I will build one. All I need is the LEMO connector. I would really like to know though why it failed in a non-surge related way at such a low current level. Previously I have only seen them fail where it could have been surge current related. On Sat, 24 Mar 2012 06:45:12 -0700 (PDT), J. Forster j...@quikus.com wrote: Nope. The cap was cool because the thing was shorted and had no voltage across it. Power is V * I. As I said before, either an open or a short circuited component dissipates no power. The defective component is NOT always the hot one. A hot component is only a pointer to the fault, not necessarily the problem itself. This is especially true of fuses. Always ask Why did the fuse blow?? -John = I just tracked down a shorted tantalum in a Tektronix DM501 multimeter. It was on the output of the floating -12 volt supply bridge rectifier before the regulator. The current level was so low that it never heated up although I burned two fingers on the push-pull output transistors for the floating supply. The regulator is on a separate module but the supply was still shorted when I pulled it and the bad tantalum was the only part left. I have not seen a shorted tantalum before where it could not be surge current related until now. On Sat, 24 Mar 2012 00:08:12 -0400, Peter Gottlieb n...@verizon.net wrote: I had a HP 3326 which had a power supply in foldback. All the modules are inaccessible unless you have a rather rare set of extenders anyway. The voltmeter method quickly led me to the board and a bench supply and meter again to the shorted cap. Very easy. Other times I've borrowed the FLIR camera from work, also taught the new EEs that trick as well. It is a true lifesaver on dense surface mount boards. I haven't tried the liquid crystal sheet but it seems like an interesting idea so long as everything is about the same height. Peter On Mar 23, 2012, at 11:53 PM, li...@lazygranch.com wrote: Prior to emission or IR microscope technology, liquid crystals was how you found hotspots on ICs. I've done this with a goop that you dispense with a syringe. One trick to make this more sensitive is you bring a soldering iron close to the liquid crystals. Not so close as to cause a change, but you get them closer to the phase change point. -Original Message- From: Skip Withrow skip.with...@gmail.com Sender: time-nuts-boun...@febo.com Date: Fri, 23 Mar 2012 21:07:45 To: time-nuts@febo.com Reply-To: swith...@alum.mit.edu, Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] Anyone familiar with SR-620 repair? You don't need expensive test equipment to find this kind of problem. What I use is a sheet of liquid crystal film with a transition temperature just slightly above your room temperature. Just lay it on the circuit board and you can find where the power is being dissipated (even if pretty small) by watching the colors change. I think Omega Engineering sells a 8.5 x 11 sheet for about $18 if memory serves me. I have used this trick many times and it works great to find shorted (bypass) caps. No disconnecting anything, no milliohm meters, no 4 or 5 digit voltmeters. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Not w/ that instrument, but try the following. I assume you have the book w/ schematics. Power the unit and with a DMM or VOM check the PS rails to see which is sick. From the book, locate all bypass caps on that rail. Put your DMM across each in turn. The one with the lowest drop is likely the culprit. If there is more than one w/ low voltage, it's likely the one closest to the power supply. You might try touching all the bypass caps to see if any are runni9ng hot. This does not always work, because zero voltage or zero current dissipates nothing. -John == My SRS SR-620 counter died last weekend. After superficial troubleshooting, it looks like there's probably a short on one of the power supply rails. Symptom is that nothing lights up when power is turned on, but one or more of the three terminal regulators gets very, very hot (can't tell which one since they're all bolted to the side rail as heat sink). The unit had been running continuously for several weeks when the failure occurred. I just learned from SRS that they charge a flat rate 25% of the current list price for repairs! (To be fair, if you're the original purchaser, it's only 20%.) The SR620 currently lists for about $5K, so we're talking about a mighty expensive shorted cap (if that's what it is)! Anyway, has anyone here troubleshot an SR-620 with a problem like this, or have any general insights about working on one of these beasts? Thanks, John ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Great advice. I have the manual, but it doesn't include schematics. I think someone on the list has a PDF of the schematics, so I'll be digging around for that before I start digging into the box. John On 3/23/2012 2:36 PM, J. Forster wrote: Not w/ that instrument, but try the following. I assume you have the book w/ schematics. Power the unit and with a DMM or VOM check the PS rails to see which is sick. From the book, locate all bypass caps on that rail. Put your DMM across each in turn. The one with the lowest drop is likely the culprit. If there is more than one w/ low voltage, it's likely the one closest to the power supply. You might try touching all the bypass caps to see if any are runni9ng hot. This does not always work, because zero voltage or zero current dissipates nothing. -John == My SRS SR-620 counter died last weekend. After superficial troubleshooting, it looks like there's probably a short on one of the power supply rails. Symptom is that nothing lights up when power is turned on, but one or more of the three terminal regulators gets very, very hot (can't tell which one since they're all bolted to the side rail as heat sink). The unit had been running continuously for several weeks when the failure occurred. I just learned from SRS that they charge a flat rate 25% of the current list price for repairs! (To be fair, if you're the original purchaser, it's only 20%.) The SR620 currently lists for about $5K, so we're talking about a mighty expensive shorted cap (if that's what it is)! Anyway, has anyone here troubleshot an SR-620 with a problem like this, or have any general insights about working on one of these beasts? Thanks, John ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Very nice to see schematics. I do not have a sr620. Looks good. You have been given some great guidance on seeing what supply is loaded. Thats the first step. Then I look for those nasty tear drop tants. Sometimes there is a clue they are baking or as I think John said feel them when they have been on a bit. Its possible that one of the chips has an issue try feeling those also. I see a lot of ecl so that can get nasty to troubleshoot. Regards Paul. WB8TSL On Fri, Mar 23, 2012 at 3:04 PM, Marek Peca ma...@duch.cz wrote: Great advice. I have the manual, but it doesn't include schematics. I think someone on the list has a PDF of the schematics, so I'll be digging around for that before I start digging into the box. SR620 schematics: http://rtime.felk.cvut.cz/~**pecam1/SR620_sch.pdfhttp://rtime.felk.cvut.cz/~pecam1/SR620_sch.pdf Good luck please report your results, Marek __**_ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/** mailman/listinfo/time-nutshttps://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
On 03/23/2012 07:32 PM, John Ackermann N8UR wrote: My SRS SR-620 counter died last weekend. After superficial troubleshooting, it looks like there's probably a short on one of the power supply rails. Symptom is that nothing lights up when power is turned on, but one or more of the three terminal regulators gets very, very hot (can't tell which one since they're all bolted to the side rail as heat sink). The unit had been running continuously for several weeks when the failure occurred. I just learned from SRS that they charge a flat rate 25% of the current list price for repairs! (To be fair, if you're the original purchaser, it's only 20%.) The SR620 currently lists for about $5K, so we're talking about a mighty expensive shorted cap (if that's what it is)! Anyway, has anyone here troubleshot an SR-620 with a problem like this, or have any general insights about working on one of these beasts? You have several tantal caps in there. They can have short-circuit as failure mode. Use the schematic and PDF manual to follow up. Make a note of which stabs/transistors over-heat and then turn off and try to see if any of the caps is also hot. The design has no fold-back on over-current of the power lines. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
I should have added that you can get a pretty good idea of whick branch on a PCB is drawing current by probing along the trace. This is especially useful if the rail has a bunch of branch distribution lines. Also, if the three-terminal regulator is overheating, disconnect it and power just that rail from an external, current limited supply of a volt or two. That way you don't risk trace damage. Best, -John My SRS SR-620 counter died last weekend. After superficial troubleshooting, it looks like there's probably a short on one of the power supply rails. Symptom is that nothing lights up when power is turned on, but one or more of the three terminal regulators gets very, very hot (can't tell which one since they're all bolted to the side rail as heat sink). The unit had been running continuously for several weeks when the failure occurred. I just learned from SRS that they charge a flat rate 25% of the current list price for repairs! (To be fair, if you're the original purchaser, it's only 20%.) The SR620 currently lists for about $5K, so we're talking about a mighty expensive shorted cap (if that's what it is)! Anyway, has anyone here troubleshot an SR-620 with a problem like this, or have any general insights about working on one of these beasts? Thanks, John ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
On 03/23/2012 09:30 PM, J. Forster wrote: I should have added that you can get a pretty good idea of whick branch on a PCB is drawing current by probing along the trace. This is especially useful if the rail has a bunch of branch distribution lines. Also, if the three-terminal regulator is overheating, disconnect it and power just that rail from an external, current limited supply of a volt or two. That way you don't risk trace damage. I would toss the TDR on it just for the fun of it, but a miliohm measurement should also help to locate it. Otherwise if there is no direct evidence (hot cap or other chip) lifting legs of caps on speculation can be a starter. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Shame you do not have a Hall effect probe to drag down the trace. John WA4WDL -- From: Magnus Danielson mag...@rubidium.dyndns.org Sent: Friday, March 23, 2012 4:58 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Anyone familiar with SR-620 repair? On 03/23/2012 09:30 PM, J. Forster wrote: I should have added that you can get a pretty good idea of whick branch on a PCB is drawing current by probing along the trace. This is especially useful if the rail has a bunch of branch distribution lines. Also, if the three-terminal regulator is overheating, disconnect it and power just that rail from an external, current limited supply of a volt or two. That way you don't risk trace damage. I would toss the TDR on it just for the fun of it, but a miliohm measurement should also help to locate it. Otherwise if there is no direct evidence (hot cap or other chip) lifting legs of caps on speculation can be a starter. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Hi Magnus, I very much doubt you could get anything useful out of a TDR. There is no reason I can think of that a power rail should look anything like a transmission line and the rail should be an AC short every inch or so. FWIW, -John On 03/23/2012 09:30 PM, J. Forster wrote: I should have added that you can get a pretty good idea of whick branch on a PCB is drawing current by probing along the trace. This is especially useful if the rail has a bunch of branch distribution lines. Also, if the three-terminal regulator is overheating, disconnect it and power just that rail from an external, current limited supply of a volt or two. That way you don't risk trace damage. I would toss the TDR on it just for the fun of it, but a miliohm measurement should also help to locate it. Otherwise if there is no direct evidence (hot cap or other chip) lifting legs of caps on speculation can be a starter. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Are there Hall Effect probes for chasing DC faults? I'm very familiar with the HP Logic Current Tracer, but AFAIK that is only sensitive to fast pulses, from the Logic Pulser for example. The threashold is adjustable, so maybe it will sense DC currents. If it is DC sensitive it'd be even more wonderful. I'll try it after dinner. Thanks, -John Shame you do not have a Hall effect probe to drag down the trace. John WA4WDL -- From: Magnus Danielson mag...@rubidium.dyndns.org Sent: Friday, March 23, 2012 4:58 PM To: time-nuts@febo.com Subject: Re: [time-nuts] Anyone familiar with SR-620 repair? On 03/23/2012 09:30 PM, J. Forster wrote: I should have added that you can get a pretty good idea of whick branch on a PCB is drawing current by probing along the trace. This is especially useful if the rail has a bunch of branch distribution lines. Also, if the three-terminal regulator is overheating, disconnect it and power just that rail from an external, current limited supply of a volt or two. That way you don't risk trace damage. I would toss the TDR on it just for the fun of it, but a miliohm measurement should also help to locate it. Otherwise if there is no direct evidence (hot cap or other chip) lifting legs of caps on speculation can be a starter. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
HP once made a kit with DIP logic clip, logic probe, logic pulser, and current tracer. Pulser and tracer made finding shorts pretty easy. For the SR-620 you could disconnect the regulator and inject current pulses there, follow them around with current tracer. The same basic trick works given a bench type pulse generator as the injector, following the current with a chopped down magnetic tape head feeding a scope (or spec analyzer?). Been there, done that. Made my own RF type probe with just a small coil at the tip. Have the HP logic kit as well. Bob LaJeunesse ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Here is a trick or two that may work: feed a very small AC voltage with say 1KHz and 10mV into the bad power rail. It won't hurt anything. Then use an old cassette players' magnetic pickup and amplifier to follow the signal to the short. No need for expensive hall effect meters. Another trick that I often use is force-feed power into the bad power rail. If it's a 5V rail, then say 5V at 2A. That can work by having the bad part get hot really quickly, by allowing you to DC probe with a millivolt setting, or it can backfire if it's a tant cap by blowing it up. I would use that only as a last resort if the first trick didn't work, as the second trick can be dangerous! So please be careful, any repair should be done only with proper equipment (using a 110V isolation transformer for example)... bye, Said In a message dated 3/23/2012 14:13:57 Pacific Daylight Time, j...@quikus.com writes: Are there Hall Effect probes for chasing DC faults? I'm very familiar with the HP Logic Current Tracer, but AFAIK that is only sensitive to fast pulses, from the Logic Pulser for example. The threashold is adjustable, so maybe it will sense DC currents. If it is DC sensitive it'd be even more wonderful. I'll try it after dinner. Thanks, -John ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
One technique that works for me is to remove the bolts holding the regulator tabs against the heat sink, and ensure that the tabs are not touching same. Then, starting with the unit at ambient temperature, apply power for ten seconds or so, and then use an IR temperature sensor to determine which regulator is getting hot. Lacking an IR tool, a fingertip will suffice. This technique will quickly identify which part of the circuitry is drawing excessive power. Needless to say, the power-on time must be short to avoid damaging the regulators while operating without a heat sink. 73, Eric Lemmon WB6FLY ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Here is a trick or two that may work: feed a very small AC voltage with say 1KHz and 10mV into the bad power rail. It won't hurt anything. Then use an old cassette players' magnetic pickup and amplifier to follow the signal to the short. No need for expensive hall effect meters. Good bypass caps are near AC shorts. I've not tried it, but am not optomistic. It would work on stuck signals lines, but not well on power, IMO. Another trick that I often use is force-feed power into the bad power rail. If it's a 5V rail, then say 5V at 2A. That can work by having the bad part get hot really quickly, by allowing you to DC probe with a millivolt setting, or it can backfire if it's a tant cap by blowing it up. I would use that only as a last resort if the first trick didn't work, as the second trick can be dangerous! Be aware, you can overheat and burn out PCB traces or vias. Small capacitors don't make a real mess when they poip, but I would most certainly wear glasses. -John == So please be careful, any repair should be done only with proper equipment (using a 110V isolation transformer for example)... bye, Said In a message dated 3/23/2012 14:13:57 Pacific Daylight Time, j...@quikus.com writes: Are there Hall Effect probes for chasing DC faults? I'm very familiar with the HP Logic Current Tracer, but AFAIK that is only sensitive to fast pulses, from the Logic Pulser for example. The threashold is adjustable, so maybe it will sense DC currents. If it is DC sensitive it'd be even more wonderful. I'll try it after dinner. Thanks, -John ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
The HP 547A Current Tracer is an AC only instrument, as I thought. It uses a coil as a pickup, not a Hall device. See: http://cp.literature.agilent.com/litweb/pdf/00547-90006.pdf Page 11 Too bad. :(( -John == In a message dated 3/23/2012 14:13:57 Pacific Daylight Time, j...@quikus.com writes: Are there Hall Effect probes for chasing DC faults? I'm very familiar with the HP Logic Current Tracer, but AFAIK that is only sensitive to fast pulses, from the Logic Pulser for example. The threashold is adjustable, so maybe it will sense DC currents. If it is DC sensitive it'd be even more wonderful. I'll try it after dinner. Thanks, -John ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Shouldn't be too bad, a 10uF cap would have 15 Ohms impedance at 1KHz, 150 Ohms at 100Hz, and one could inject at different places on the trace... away from the big bypass caps. Doing the same with DC and a simple multimeter should work too. bye, Said In a message dated 3/23/2012 14:31:42 Pacific Daylight Time, j...@quikus.com writes: Here is a trick or two that may work: feed a very small AC voltage with say 1KHz and 10mV into the bad power rail. It won't hurt anything. Then use an old cassette players' magnetic pickup and amplifier to follow the signal to the short. No need for expensive hall effect meters. Good bypass caps are near AC shorts. I've not tried it, but am not optomistic. It would work on stuck signals lines, but not well on power, IMO. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Most instrument PCBs have scores of bypass caps... all in parallel. -John = Shouldn't be too bad, a 10uF cap would have 15 Ohms impedance at 1KHz, 150 Ohms at 100Hz, and one could inject at different places on the trace... away from the big bypass caps. Doing the same with DC and a simple multimeter should work too. bye, Said In a message dated 3/23/2012 14:31:42 Pacific Daylight Time, j...@quikus.com writes: Here is a trick or two that may work: feed a very small AC voltage with say 1KHz and 10mV into the bad power rail. It won't hurt anything. Then use an old cassette players' magnetic pickup and amplifier to follow the signal to the short. No need for expensive hall effect meters. Good bypass caps are near AC shorts. I've not tried it, but am not optomistic. It would work on stuck signals lines, but not well on power, IMO. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
In my opinion, if you are hunting for a short, there is a little to do with the current: it is always the same, better use a voltmeter/millivoltmeter and hunt for the least voltage across capacitors or the greatest voltage drop on traces... On Fri, Mar 23, 2012 at 11:36 PM, Geoff Blake melecert...@gmail.com wrote: On our side of the pond there is/was a device called the Polar Toneohm. It used a hall effect device to translate the current flowing in a track to a tone - rising pitch, higher current. These could be very effective in finding shorts in power rails etc, also in multi-layer boards. Google Toneohm and you will see. Geoff -- # Geoff Blake, G8GNZJO01fq: Chelmsford, Essex, UK ge...@palaemon.co.ukor melecert...@gmail.com Using Linux: Ubuntu 11.04 on Intel or Debian on UltraSparc and even on the NAS. Avoiding Micro$oft like the plague. # ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
SRS620 schematics are on ko4bb.com Didier KO4BB Sent from my BlackBerry Wireless thingy while I do other things... -Original Message- From: John Ackermann N8UR j...@febo.com Sender: time-nuts-boun...@febo.com Date: Fri, 23 Mar 2012 14:46:07 To: j...@quikus.com; Discussion of precise time and frequency measurementtime-nuts@febo.com Reply-To: Discussion of precise time and frequency measurement time-nuts@febo.com Subject: Re: [time-nuts] Anyone familiar with SR-620 repair? Great advice. I have the manual, but it doesn't include schematics. I think someone on the list has a PDF of the schematics, so I'll be digging around for that before I start digging into the box. John On 3/23/2012 2:36 PM, J. Forster wrote: Not w/ that instrument, but try the following. I assume you have the book w/ schematics. Power the unit and with a DMM or VOM check the PS rails to see which is sick. From the book, locate all bypass caps on that rail. Put your DMM across each in turn. The one with the lowest drop is likely the culprit. If there is more than one w/ low voltage, it's likely the one closest to the power supply. You might try touching all the bypass caps to see if any are runni9ng hot. This does not always work, because zero voltage or zero current dissipates nothing. -John == My SRS SR-620 counter died last weekend. After superficial troubleshooting, it looks like there's probably a short on one of the power supply rails. Symptom is that nothing lights up when power is turned on, but one or more of the three terminal regulators gets very, very hot (can't tell which one since they're all bolted to the side rail as heat sink). The unit had been running continuously for several weeks when the failure occurred. I just learned from SRS that they charge a flat rate 25% of the current list price for repairs! (To be fair, if you're the original purchaser, it's only 20%.) The SR620 currently lists for about $5K, so we're talking about a mighty expensive shorted cap (if that's what it is)! Anyway, has anyone here troubleshot an SR-620 with a problem like this, or have any general insights about working on one of these beasts? Thanks, John ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
Prior to emission or IR microscope technology, liquid crystals was how you found hotspots on ICs. I've done this with a goop that you dispense with a syringe. One trick to make this more sensitive is you bring a soldering iron close to the liquid crystals. Not so close as to cause a change, but you get them closer to the phase change point. -Original Message- From: Skip Withrow skip.with...@gmail.com Sender: time-nuts-boun...@febo.com Date: Fri, 23 Mar 2012 21:07:45 To: time-nuts@febo.com Reply-To: swith...@alum.mit.edu, Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] Anyone familiar with SR-620 repair? You don't need expensive test equipment to find this kind of problem. What I use is a sheet of liquid crystal film with a transition temperature just slightly above your room temperature. Just lay it on the circuit board and you can find where the power is being dissipated (even if pretty small) by watching the colors change. I think Omega Engineering sells a 8.5 x 11 sheet for about $18 if memory serves me. I have used this trick many times and it works great to find shorted (bypass) caps. No disconnecting anything, no milliohm meters, no 4 or 5 digit voltmeters. Regards, Skip Withrow ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
I had a HP 3326 which had a power supply in foldback. All the modules are inaccessible unless you have a rather rare set of extenders anyway. The voltmeter method quickly led me to the board and a bench supply and meter again to the shorted cap. Very easy. Other times I've borrowed the FLIR camera from work, also taught the new EEs that trick as well. It is a true lifesaver on dense surface mount boards. I haven't tried the liquid crystal sheet but it seems like an interesting idea so long as everything is about the same height. Peter On Mar 23, 2012, at 11:53 PM, li...@lazygranch.com wrote: Prior to emission or IR microscope technology, liquid crystals was how you found hotspots on ICs. I've done this with a goop that you dispense with a syringe. One trick to make this more sensitive is you bring a soldering iron close to the liquid crystals. Not so close as to cause a change, but you get them closer to the phase change point. -Original Message- From: Skip Withrow skip.with...@gmail.com Sender: time-nuts-boun...@febo.com Date: Fri, 23 Mar 2012 21:07:45 To: time-nuts@febo.com Reply-To: swith...@alum.mit.edu, Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] Anyone familiar with SR-620 repair? You don't need expensive test equipment to find this kind of problem. What I use is a sheet of liquid crystal film with a transition temperature just slightly above your room temperature. Just lay it on the circuit board and you can find where the power is being dissipated (even if pretty small) by watching the colors change. I think Omega Engineering sells a 8.5 x 11 sheet for about $18 if memory serves me. I have used this trick many times and it works great to find shorted (bypass) caps. No disconnecting anything, no milliohm meters, no 4 or 5 digit voltmeters. Regards, Skip Withrow ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Anyone familiar with SR-620 repair?
I just tracked down a shorted tantalum in a Tektronix DM501 multimeter. It was on the output of the floating -12 volt supply bridge rectifier before the regulator. The current level was so low that it never heated up although I burned two fingers on the push-pull output transistors for the floating supply. The regulator is on a separate module but the supply was still shorted when I pulled it and the bad tantalum was the only part left. I have not seen a shorted tantalum before where it could not be surge current related until now. On Sat, 24 Mar 2012 00:08:12 -0400, Peter Gottlieb n...@verizon.net wrote: I had a HP 3326 which had a power supply in foldback. All the modules are inaccessible unless you have a rather rare set of extenders anyway. The voltmeter method quickly led me to the board and a bench supply and meter again to the shorted cap. Very easy. Other times I've borrowed the FLIR camera from work, also taught the new EEs that trick as well. It is a true lifesaver on dense surface mount boards. I haven't tried the liquid crystal sheet but it seems like an interesting idea so long as everything is about the same height. Peter On Mar 23, 2012, at 11:53 PM, li...@lazygranch.com wrote: Prior to emission or IR microscope technology, liquid crystals was how you found hotspots on ICs. I've done this with a goop that you dispense with a syringe. One trick to make this more sensitive is you bring a soldering iron close to the liquid crystals. Not so close as to cause a change, but you get them closer to the phase change point. -Original Message- From: Skip Withrow skip.with...@gmail.com Sender: time-nuts-boun...@febo.com Date: Fri, 23 Mar 2012 21:07:45 To: time-nuts@febo.com Reply-To: swith...@alum.mit.edu, Discussion of precise time and frequency measurement time-nuts@febo.com Subject: [time-nuts] Anyone familiar with SR-620 repair? You don't need expensive test equipment to find this kind of problem. What I use is a sheet of liquid crystal film with a transition temperature just slightly above your room temperature. Just lay it on the circuit board and you can find where the power is being dissipated (even if pretty small) by watching the colors change. I think Omega Engineering sells a 8.5 x 11 sheet for about $18 if memory serves me. I have used this trick many times and it works great to find shorted (bypass) caps. No disconnecting anything, no milliohm meters, no 4 or 5 digit voltmeters. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
