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.