Re: [time-nuts] HP 5328 PSU nightmare... Or stupid engineer, you decide...
Hi Douglas, I have no experience with this beast but to draw this sort of current it points to a possible bypass cap short. If there are any dipped tants in there, there is a high possibility that one or more of them have gone short. If you have a good 4-wire ohm meter and a kelvin probe, just check round to see if you can find some that are very low ohms before you end up un-soldering them. Other than that it's down to un-soldering off parts of the circuit to see where the big load is. Logical isolation always seems the most sensible way to isolate circuits but the number of time this has let me down so I frequently use a binary chop method and make no 'educated guesses'. A variac works well to drop the voltage but you may not easily find the fault on a a switcher this way. At the very least you will always need good ways to un-solder things. I'm sure we will all look forward to your input to the group and it will be interesting to hear in what field of time-nuttiness you work. Regards, Steve 2009/9/10 Douglas Wire - PUPCo Studios cont...@pupcostudios.com: Good day everyone and thank you all for hosting this wonderful community and allowing me to participate. I have several HP5328 with the “really- nice” newer 10811-x Oscillators in them. I have found while I have used the good old gold trace reliable HP instruments all of my life, these units have been especially difficult. The first unit the 4500uF electrolytic’s went bad and produced essentially a dead short; an easy enough repair for me to not only track down in minutes, but it only takes a straight bit screwdriver to fix in seconds! Now our second unit has been giving me fits and while I would agree 100% with one of the posts I saw here about how well HP did not only with their schematics, but also the wonderful troubleshooting flow charts usually make repairs on any of their old units a breeze. Sadly I have a unit here that is giving us fits! It is a PSU issue and not related to the Motherboard or any of the cards as I tested it with everything unhooked/ unsoldered and still got the same result. It is quite similar to what we see when we get an old HP unit that has a fried cap and is darn near creating a short to ground, but alas I simply cannot find the problem (I am sure it is starring me in the face is and I just can’t see it…) What I am seeing is super high current flow through the R1 (I believe, but HP’s every unit I have ever serviced had.47Ω resistor, NOT a 22-Ω as is stated in the schematic…) that leads to F1. The troubleshooting is complicated by the fact that unless I want to smoke that heavy duty, relatively close tolerance resistor, I cannot even check voltages anywhere for it will blow the fuse or if I put a slow blow to try and catch some measurements in a second or two, well that is not very feasible either. If I had to guess, I would say it has either a cap that has fried, outside chance of a transformer issue, or the way this thing reacts, pretty well an effective dead short somewhere, but I will be damned if I can find the problem anywhere. I replaced the bad and 4500uF caps as well as the rectifier, wondering if part of it had blown with no change in its issues. One cannot follow the flow cart to much of anything other than boxes that say look for a short, but so many areas one tests even on a perfectly working unit come clear down near the zero Ω point even when they are operating correctly. I apologize if 1) this is not a clear email that anyone can easily understand and 2) I almost feel embarrassed to ask anyone for advice from their practical experience, for I feel as If I should easily be able to get to the bottom of this in a matter of minutes with the wonderful data HP provides us all for these old workhorses. So if anyone has run into a problem such as this in the past where working the flow chart only yields No, No, No - check for shorts and has any advice for how I might logically proceed, or what in fact you have found out in dealing with a similar problem, it would be of great help, as we need this in-service ASAP, but I guess I just cannot see the forest for the tress in front of me or something here… Any advise, suggestions would be greatly appreciated. I would like to become a more active participant here with all I can contribute, which hopefully soon should be a lot as I am doing some innovative timing and generation processes that I am relatively sure the outcome and data from derived from it could be of great benefit to the TIME- NUTS userbase here. Thanks and don’t be too hard on me for asking (what to me sounds like a stupid amateur question) but I am either too tired to reason correctly, or it is just one of those very pesky problems, that hopefully someone has identified before and might be able to enlighten us over. I am begiinign to wonder if a voltage regulator might be responsible, but I am at a loss at the moment and have
Re: [time-nuts] HP 5328 PSU nightmare... Or stupid engineer, you decide...
Douglas, there are lots of folks out there that are much more familiar with the 5328A, but here is what I think about it at a first glance. If F1 blows quickly, there is a serious overload / short situation. Don't try fixing by swapping fuses. If you can't measure a short (that would be the first thing to look for), THEN you might have luck checking the overvoltage protection circuit. It consists of power Z-diode CR11. Chances are the +15 volts are out of spec (probably due to a faulty regulator circuit), so the 17V diode shorts the voltage and lets F1 blow. You can unsolder CR11 to see if that is what happens. However, disconnect everything from the +15 volts before you switch on again. Otherwise you risk serious damage to other circuitry. Hope that helps. Good luck! Adrian Douglas Wire - PUPCo Studios schrieb: Good day everyone and thank you all for hosting this wonderful community and allowing me to participate. I have several HP5328 with the “really- nice” newer 10811-x Oscillators in them. I have found while I have used the good old gold trace reliable HP instruments all of my life, these units have been especially difficult. The first unit the 4500uF electrolytic’s went bad and produced essentially a dead short; an easy enough repair for me to not only track down in minutes, but it only takes a straight bit screwdriver to fix in seconds! Now our second unit has been giving me fits and while I would agree 100% with one of the posts I saw here about how well HP did not only with their schematics, but also the wonderful troubleshooting flow charts usually make repairs on any of their old units a breeze. Sadly I have a unit here that is giving us fits! It is a PSU issue and not related to the Motherboard or any of the cards as I tested it with everything unhooked/ unsoldered and still got the same result. It is quite similar to what we see when we get an old HP unit that has a fried cap and is darn near creating a short to ground, but alas I simply cannot find the problem (I am sure it is starring me in the face is and I just can’t see it…) What I am seeing is super high current flow through the R1 (I believe, but HP’s every unit I have ever serviced had.47Ω resistor, NOT a 22-Ω as is stated in the schematic…) that leads to F1. The troubleshooting is complicated by the fact that unless I want to smoke that heavy duty, relatively close tolerance resistor, I cannot even check voltages anywhere for it will blow the fuse or if I put a slow blow to try and catch some measurements in a second or two, well that is not very feasible either. If I had to guess, I would say it has either a cap that has fried, outside chance of a transformer issue, or the way this thing reacts, pretty well an effective dead short somewhere, but I will be damned if I can find the problem anywhere. I replaced the bad and 4500uF caps as well as the rectifier, wondering if part of it had blown with no change in its issues. One cannot follow the flow cart to much of anything other than boxes that say look for a short, but so many areas one tests even on a perfectly working unit come clear down near the zero Ω point even when they are operating correctly. I apologize if 1) this is not a clear email that anyone can easily understand and 2) I almost feel embarrassed to ask anyone for advice from their practical experience, for I feel as If I should easily be able to get to the bottom of this in a matter of minutes with the wonderful data HP provides us all for these old workhorses. So if anyone has run into a problem such as this in the past where working the flow chart only yields No, No, No - check for shorts and has any advice for how I might logically proceed, or what in fact you have found out in dealing with a similar problem, it would be of great help, as we need this in-service ASAP, but I guess I just cannot see the forest for the tress in front of me or something here… Any advise, suggestions would be greatly appreciated. I would like to become a more active participant here with all I can contribute, which hopefully soon should be a lot as I am doing some innovative timing and generation processes that I am relatively sure the outcome and data from derived from it could be of great benefit to the TIME- NUTS userbase here. Thanks and don’t be too hard on me for asking (what to me sounds like a stupid amateur question) but I am either too tired to reason correctly, or it is just one of those very pesky problems, that hopefully someone has identified before and might be able to enlighten us over. I am begiinign to wonder if a voltage regulator might be responsible, but I am at a loss at the moment and have not had enough sleep to properly think this repair through… Thank you again everyone! Warm regards, Douglas M. Wire, GED, FNA, PUPCo Studios, PUPCo Research Group ___
Re: [time-nuts] HP 5328 PSU nightmare... Or stupid engineer, you decide...
I'm not familiar with this particular instrument, but a standard technique for linear power supplies is to hook it up to a variac. This lets you turn down the line voltage so you can do some measurements without smoking the system. Brent Douglas Wire - PUPCo Studios wrote: Good day everyone and thank you all for hosting this wonderful community and allowing me to participate. I have several HP5328 with the “really- nice” newer 10811-x Oscillators in them. I have found while I have used the good old gold trace reliable HP instruments all of my life, these units have been especially difficult. The first unit the 4500uF electrolytic’s went bad and produced essentially a dead short; an easy enough repair for me to not only track down in minutes, but it only takes a straight bit screwdriver to fix in seconds! Now our second unit has been giving me fits and while I would agree 100% with one of the posts I saw here about how well HP did not only with their schematics, but also the wonderful troubleshooting flow charts usually make repairs on any of their old units a breeze. Sadly I have a unit here that is giving us fits! It is a PSU issue and not related to the Motherboard or any of the cards as I tested it with everything unhooked/ unsoldered and still got the same result. It is quite similar to what we see when we get an old HP unit that has a fried cap and is darn near creating a short to ground, but alas I simply cannot find the problem (I am sure it is starring me in the face is and I just can’t see it…) What I am seeing is super high current flow through the R1 (I believe, but HP’s every unit I have ever serviced had.47Ω resistor, NOT a 22-Ω as is stated in the schematic…) that leads to F1. The troubleshooting is complicated by the fact that unless I want to smoke that heavy duty, relatively close tolerance resistor, I cannot even check voltages anywhere for it will blow the fuse or if I put a slow blow to try and catch some measurements in a second or two, well that is not very feasible either. If I had to guess, I would say it has either a cap that has fried, outside chance of a transformer issue, or the way this thing reacts, pretty well an effective dead short somewhere, but I will be damned if I can find the problem anywhere. I replaced the bad and 4500uF caps as well as the rectifier, wondering if part of it had blown with no change in its issues. One cannot follow the flow cart to much of anything other than boxes that say look for a short, but so many areas one tests even on a perfectly working unit come clear down near the zero Ω point even when they are operating correctly. I apologize if 1) this is not a clear email that anyone can easily understand and 2) I almost feel embarrassed to ask anyone for advice from their practical experience, for I feel as If I should easily be able to get to the bottom of this in a matter of minutes with the wonderful data HP provides us all for these old workhorses. So if anyone has run into a problem such as this in the past where working the flow chart only yields No, No, No - check for shorts and has any advice for how I might logically proceed, or what in fact you have found out in dealing with a similar problem, it would be of great help, as we need this in-service ASAP, but I guess I just cannot see the forest for the tress in front of me or something here… Any advise, suggestions would be greatly appreciated. I would like to become a more active participant here with all I can contribute, which hopefully soon should be a lot as I am doing some innovative timing and generation processes that I am relatively sure the outcome and data from derived from it could be of great benefit to the TIME- NUTS userbase here. Thanks and don’t be too hard on me for asking (what to me sounds like a stupid amateur question) but I am either too tired to reason correctly, or it is just one of those very pesky problems, that hopefully someone has identified before and might be able to enlighten us over. I am begiinign to wonder if a voltage regulator might be responsible, but I am at a loss at the moment and have not had enough sleep to properly think this repair through… Thank you again everyone! Warm regards, Douglas M. Wire, GED, FNA, PUPCo Studios, PUPCo Research Group ___ 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] HP 5328 PSU nightmare... Or stupid engineer, you decide...
Neither the linear regulators nor the switching regulators in the 5328A have any explicit current limiting circuitry other than that provided by the pass transistor current gain and the limited current available from the pass element driver. The only protection against long term load faults is provided by the fuses at the regulator inputs. However these fuses don't protect against shorted rectifier output filter capacitors etc. Bruce Brent Gordon wrote: I'm not familiar with this particular instrument, but a standard technique for linear power supplies is to hook it up to a variac. This lets you turn down the line voltage so you can do some measurements without smoking the system. Brent Douglas Wire - PUPCo Studios wrote: Good day everyone and thank you all for hosting this wonderful community and allowing me to participate. I have several HP5328 with the “really- nice” newer 10811-x Oscillators in them. I have found while I have used the good old gold trace reliable HP instruments all of my life, these units have been especially difficult. The first unit the 4500uF electrolytic’s went bad and produced essentially a dead short; an easy enough repair for me to not only track down in minutes, but it only takes a straight bit screwdriver to fix in seconds! Now our second unit has been giving me fits and while I would agree 100% with one of the posts I saw here about how well HP did not only with their schematics, but also the wonderful troubleshooting flow charts usually make repairs on any of their old units a breeze. Sadly I have a unit here that is giving us fits! It is a PSU issue and not related to the Motherboard or any of the cards as I tested it with everything unhooked/ unsoldered and still got the same result. It is quite similar to what we see when we get an old HP unit that has a fried cap and is darn near creating a short to ground, but alas I simply cannot find the problem (I am sure it is starring me in the face is and I just can’t see it…) What I am seeing is super high current flow through the R1 (I believe, but HP’s every unit I have ever serviced had.47Ω resistor, NOT a 22-Ω as is stated in the schematic…) that leads to F1. The troubleshooting is complicated by the fact that unless I want to smoke that heavy duty, relatively close tolerance resistor, I cannot even check voltages anywhere for it will blow the fuse or if I put a slow blow to try and catch some measurements in a second or two, well that is not very feasible either. If I had to guess, I would say it has either a cap that has fried, outside chance of a transformer issue, or the way this thing reacts, pretty well an effective dead short somewhere, but I will be damned if I can find the problem anywhere. I replaced the bad and 4500uF caps as well as the rectifier, wondering if part of it had blown with no change in its issues. One cannot follow the flow cart to much of anything other than boxes that say look for a short, but so many areas one tests even on a perfectly working unit come clear down near the zero Ω point even when they are operating correctly. I apologize if 1) this is not a clear email that anyone can easily understand and 2) I almost feel embarrassed to ask anyone for advice from their practical experience, for I feel as If I should easily be able to get to the bottom of this in a matter of minutes with the wonderful data HP provides us all for these old workhorses. So if anyone has run into a problem such as this in the past where working the flow chart only yields No, No, No - check for shorts and has any advice for how I might logically proceed, or what in fact you have found out in dealing with a similar problem, it would be of great help, as we need this in-service ASAP, but I guess I just cannot see the forest for the tress in front of me or something here… Any advise, suggestions would be greatly appreciated. I would like to become a more active participant here with all I can contribute, which hopefully soon should be a lot as I am doing some innovative timing and generation processes that I am relatively sure the outcome and data from derived from it could be of great benefit to the TIME- NUTS userbase here. Thanks and don’t be too hard on me for asking (what to me sounds like a stupid amateur question) but I am either too tired to reason correctly, or it is just one of those very pesky problems, that hopefully someone has identified before and might be able to enlighten us over. I am begiinign to wonder if a voltage regulator might be responsible, but I am at a loss at the moment and have not had enough sleep to properly think this repair through… Thank you again everyone! Warm regards, Douglas M. Wire, GED, FNA, PUPCo Studios, PUPCo Research Group ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to
Re: [time-nuts] HP 5328 PSU nightmare... Or stupid engineer, you decide...
I'm not familiar with this particular instrument, but a standard technique for linear power supplies is to hook it up to a variac. This lets you turn down the line voltage so you can do some measurements without smoking the system. Brent Douglas Wire - PUPCo Studios wrote: Good day everyone and thank you all for hosting this wonderful community and allowing me to participate. I have several HP5328 with the ?really- nice? newer 10811-x Oscillators in them. I have found while I have used the good old gold trace reliable HP instruments all of my life, these units have been especially difficult. The first unit the 4500uF electrolytic?s went bad and produced essentially a dead short; an easy enough repair for me to not only track down in minutes, but it only takes a straight bit screwdriver to fix in seconds! Now our second unit has been giving me fits and while I would agree 100% with one of the posts I saw here about how well HP did not only with their schematics, but also the wonderful troubleshooting flow charts usually make repairs on any of their old units a breeze. Sadly I have a unit here that is giving us fits! It is a PSU issue and not related to the Motherboard or any of the cards as I tested it with everything unhooked/ unsoldered and still got the same result. It is quite similar to what we see when we get an old HP unit that has a fried cap and is darn near creating a short to ground, but alas I simply cannot find the problem (I am sure it is starring me in the face is and I just can?t see it?) What I am seeing is super high current flow through the R1 (I believe, but HP?s every unit I have ever serviced had.47? resistor, NOT a 22-? as is stated in the schematic?) that leads to F1. The troubleshooting is complicated by the fact that unless I want to smoke that heavy duty, relatively close tolerance resistor, I cannot even check voltages anywhere for it will blow the fuse or if I put a slow blow to try and catch some measurements in a second or two, well that is not very feasible either. If I had to guess, I would say it has either a cap that has fried, outside chance of a transformer issue, or the way this thing reacts, pretty well an effective dead short somewhere, but I will be damned if I can find the problem anywhere. I replaced the bad and 4500uF caps as well as the rectifier, wondering if part of it had blown with no change in its issues. One cannot follow the flow cart to much of anything other than boxes that say look for a short, but so many areas one tests even on a perfectly working unit come clear down near the zero ? point even when they are operating correctly. I apologize if 1) this is not a clear email that anyone can easily understand and 2) I almost feel embarrassed to ask anyone for advice from their practical experience, for I feel as If I should easily be able to get to the bottom of this in a matter of minutes with the wonderful data HP provides us all for these old workhorses. So if anyone has run into a problem such as this in the past where working the flow chart only yields No, No, No - check for shorts and has any advice for how I might logically proceed, or what in fact you have found out in dealing with a similar problem, it would be of great help, as we need this in-service ASAP, but I guess I just cannot see the forest for the tress in front of me or something here? Any advise, suggestions would be greatly appreciated. ... Warm regards, Douglas M. Wire, GED, FNA, PUPCo Studios, PUPCo Research Group Douglas, Start by making sure that the line voltage switch is set correctly. Barring that as a cause of the problem, you will have to start removing components that are fed by the +12V supply until the overcurrent is gone. First choice would be CR1 (12V Zener), then ICs U1, U2, U3, U4 and U5. When bad component is removed, the current should drop back to normal, or slightly less. That might be a lot of unsoldering, but unless you want to start cutting traces on the PCB, it's the only way to proceed. If you have a good ESR meter, it can be used as a low ohms meter to locate a short or low resistance. You might remove R1 and install a higher value, higher wattage resistor so that you avoid further damage while you make measurements. Measure the raw supply voltage (+25V); make sure that it's the right voltage and low ripple. Measure the voltage drop across R1 in an operating instrument, so that you have a reference of what to look for in the bad guy. From the voltage drop, you can calculate the current going through it. Use a sensitive voltmeter (5 digits or better; you want to see millivolt drops along the traces) to trace the voltage drops along the circuit traces to find where the majority of the current is going. Good luck with the troubleshooting. Dave M masondg44 at comcast dot net ___ time-nuts mailing list -- time-nuts@febo.com To
Re: [time-nuts] HP 5328 PSU nightmare... Or stupid engineer, you decide...
Hi Dave, I think we've all lost some hair while working on a stubborn problem. Hang in there. As mentioned by Brent Gordon, the Variac is your friend in situations like this. If you don't have one, you can wire a light bulb in series with the power cord. Use 40,60,100 watt - whatever you need. This will limit the current so you can search for the short without blowing fuses or letting the magic smoke out. The Variac is preferred because you may find that everything looks good until you hit X volts. The light bulb obviously isn't that selective. Ed Douglas Wire - PUPCo Studios wrote: Good day everyone and thank you all for hosting this wonderful community and allowing me to participate. I have several HP5328 with the “really- nice” newer 10811-x Oscillators in them. I have found while I have used the good old gold trace reliable HP instruments all of my life, these units have been especially difficult. The first unit the 4500uF electrolytic’s went bad and produced essentially a dead short; an easy enough repair for me to not only track down in minutes, but it only takes a straight bit screwdriver to fix in seconds! Now our second unit has been giving me fits and while I would agree 100% with one of the posts I saw here about how well HP did not only with their schematics, but also the wonderful troubleshooting flow charts usually make repairs on any of their old units a breeze. Sadly I have a unit here that is giving us fits! It is a PSU issue and not related to the Motherboard or any of the cards as I tested it with everything unhooked/ unsoldered and still got the same result. It is quite similar to what we see when we get an old HP unit that has a fried cap and is darn near creating a short to ground, but alas I simply cannot find the problem (I am sure it is starring me in the face is and I just can’t see it…) What I am seeing is super high current flow through the R1 (I believe, but HP’s every unit I have ever serviced had.47Ω resistor, NOT a 22-Ω as is stated in the schematic…) that leads to F1. The troubleshooting is complicated by the fact that unless I want to smoke that heavy duty, relatively close tolerance resistor, I cannot even check voltages anywhere for it will blow the fuse or if I put a slow blow to try and catch some measurements in a second or two, well that is not very feasible either. If I had to guess, I would say it has either a cap that has fried, outside chance of a transformer issue, or the way this thing reacts, pretty well an effective dead short somewhere, but I will be damned if I can find the problem anywhere. I replaced the bad and 4500uF caps as well as the rectifier, wondering if part of it had blown with no change in its issues. One cannot follow the flow cart to much of anything other than boxes that say look for a short, but so many areas one tests even on a perfectly working unit come clear down near the zero Ω point even when they are operating correctly. I apologize if 1) this is not a clear email that anyone can easily understand and 2) I almost feel embarrassed to ask anyone for advice from their practical experience, for I feel as If I should easily be able to get to the bottom of this in a matter of minutes with the wonderful data HP provides us all for these old workhorses. So if anyone has run into a problem such as this in the past where working the flow chart only yields No, No, No - check for shorts and has any advice for how I might logically proceed, or what in fact you have found out in dealing with a similar problem, it would be of great help, as we need this in-service ASAP, but I guess I just cannot see the forest for the tress in front of me or something here… Any advise, suggestions would be greatly appreciated. I would like to become a more active participant here with all I can contribute, which hopefully soon should be a lot as I am doing some innovative timing and generation processes that I am relatively sure the outcome and data from derived from it could be of great benefit to the TIME- NUTS userbase here. Thanks and don’t be too hard on me for asking (what to me sounds like a stupid amateur question) but I am either too tired to reason correctly, or it is just one of those very pesky problems, that hopefully someone has identified before and might be able to enlighten us over. I am begiinign to wonder if a voltage regulator might be responsible, but I am at a loss at the moment and have not had enough sleep to properly think this repair through… Thank you again everyone! Warm regards, Douglas M. Wire, GED, FNA, PUPCo Studios, PUPCo Research Group ___ 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 --
Re: [time-nuts] HP 5328 PSU nightmare... Or stupid engineer, you decide...
[variac] If you don't have one, you can wire a light bulb in series with the power cord. Use 40,60,100 watt - whatever you need. Neat. Thanks. That trick wasn't on my list. I think you can get lower wattage bulbs (at 120V). I think I've seen 25W, but I'm not sure. Old style tungsten night-lights are/were 6W. The Variac is preferred because you may find that everything looks good until you hit X volts. The light bulb obviously isn't that selective. I'd expect a light bulb to work well. If the DUT needs X volts to demonstrate the problem, it will act as a high resistance at low voltage and low resistance at high voltage. Light bulbs are (very) non-linear in the other direction. If you connect the two in series, I'd expect it to be stable at a balance point with some current, hopefully enough to debug things without burning anything out. Here is another variation ... I'm assuming you are chasing something like a short on the power rail, probably a dead bypass cap. Things get more complicated if it's only sick rather than a solidly short. If you have localized the problem to one board, power that board from a power supply with a current limit knob. You may want to solder some wires onto the board rather than using the normal connector. Crank the current up until you get enough voltage drop to be interesting but nothing is smoking. Poke around with a volt meter. If you have traces rather than a ground plane, a few amps and a reasonable meter will localize things. Even with a ground plane, it will get you pretty close. I think I remember dunking one board in a pan of Freon(?). It was some liquid that bubbled at the shorted cap. That was ~30 years ago. Maybe I'm dreaming and confusing things with another story. It does seem like a good approach. Are there any good Freon like chemicals available/legal these days? -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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] HP 5328 PSU nightmare... Or stupid engineer, you decide...
Hi, I use a Variac routinely to turn on instruments that have been unused for more than a few months. Electrolytic capacitors will often come good if slowly brought up to voltage. Recently I resurrected a WW2 Command receiver that had been stored for 40 years. I hooked up a power supply and set it to 10% of line voltage and increased it 10% at hourly intervals. Slowly warming up the device gives the electrolytics to form up, even the paper capacitors get a chance to warm and dry out a bit. For fault finding, starting at zero volts you can watch the rectifiers start to take up the load, the voltage regulators cut in when the supply reaches the regulation voltage and generally locate any overloads before the smoke gets out. The main problem is with switching regulators that abruptly cut in at some voltage, a series tungsten filament lamp helps with them to avoid smoke release. It always pays to turn it on slowly. cheers, Neville Michie ___ 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] HP 5328 PSU nightmare... Or stupid engineer, you decide...
As a kid I had an outlet in series with a screw-in bulb, with a switch across it to get full voltage. Used it very often. 73, Bob, k1REM -Original Message- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of Hal Murray Sent: Thursday, September 10, 2009 12:50 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] HP 5328 PSU nightmare... Or stupid engineer, you decide... [variac] If you don't have one, you can wire a light bulb in series with the power cord. Use 40,60,100 watt - whatever you need. Neat. Thanks. That trick wasn't on my list. I think you can get lower wattage bulbs (at 120V). I think I've seen 25W, but I'm not sure. Old style tungsten night-lights are/were 6W. The Variac is preferred because you may find that everything looks good until you hit X volts. The light bulb obviously isn't that selective. I'd expect a light bulb to work well. If the DUT needs X volts to demonstrate the problem, it will act as a high resistance at low voltage and low resistance at high voltage. Light bulbs are (very) non-linear in the other direction. If you connect the two in series, I'd expect it to be stable at a balance point with some current, hopefully enough to debug things without burning anything out. Here is another variation ... I'm assuming you are chasing something like a short on the power rail, probably a dead bypass cap. Things get more complicated if it's only sick rather than a solidly short. If you have localized the problem to one board, power that board from a power supply with a current limit knob. You may want to solder some wires onto the board rather than using the normal connector. Crank the current up until you get enough voltage drop to be interesting but nothing is smoking. Poke around with a volt meter. If you have traces rather than a ground plane, a few amps and a reasonable meter will localize things. Even with a ground plane, it will get you pretty close. I think I remember dunking one board in a pan of Freon(?). It was some liquid that bubbled at the shorted cap. That was ~30 years ago. Maybe I'm dreaming and confusing things with another story. It does seem like a good approach. Are there any good Freon like chemicals available/legal these days? -- These are my opinions, not necessarily my employer's. I hate spam. ___ 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. No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.87/2356 - Release Date: 09/09/09 17:50:00 ___ 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] HP 5328 PSU nightmare... Or stupid engineer, you decide...
Hal Murray wrote: [variac] If you don't have one, you can wire a light bulb in series with the power cord. Use 40,60,100 watt - whatever you need. Neat. Thanks. That trick wasn't on my list. I think you can get lower wattage bulbs (at 120V). I think I've seen 25W, but I'm not sure. Old style tungsten night-lights are/were 6W. Yes, and if your junk box goes back far enough, you may find some 120V Christmas tree bulbs! Not sure what their wattage is. Basically, use the smallest 120V (or 240V - depending on where you live) incandescent light bulb that gives you reasonable current / voltage in your sick circuit. You can also use lower voltage bulbs on the secondary side of a power transformer if that works better. The Variac is preferred because you may find that everything looks good until you hit X volts. The light bulb obviously isn't that selective. I'd expect a light bulb to work well. If the DUT needs X volts to demonstrate the problem, it will act as a high resistance at low voltage and low resistance at high voltage. Light bulbs are (very) non-linear in the other direction. If you connect the two in series, I'd expect it to be stable at a balance point with some current, hopefully enough to debug things without burning anything out. True, but with the light bulb you'd miss the fact that everything looks good below X volts. That could be a significant piece of info. Here is another variation ... I'm assuming you are chasing something like a short on the power rail, probably a dead bypass cap. Things get more complicated if it's only sick rather than a solidly short. If you have localized the problem to one board, power that board from a power supply with a current limit knob. You may want to solder some wires onto the board rather than using the normal connector. Crank the current up until you get enough voltage drop to be interesting but nothing is smoking. Poke around with a volt meter. If you have traces rather than a ground plane, a few amps and a reasonable meter will localize things. Even with a ground plane, it will get you pretty close. I've got a Jupiter GPS receiver that suddenly decided to start sucking silly amounts of current. Never was able to find the short on that. I've got a better meter now, maybe I'll put it back on my list of things to fix. Sigh. I think I remember dunking one board in a pan of Freon(?). It was some liquid that bubbled at the shorted cap. That was ~30 years ago. Maybe I'm dreaming and confusing things with another story. It does seem like a good approach. Are there any good Freon like chemicals available/legal these days? Freon was nice because it was non-conductive, evaporated cleanly, and wasn't flammable. I'm drawing a blank on what would be a good substitute. Ed ___ 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.
