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-xxxxx 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.