[time-nuts] HP 5328 PSU nightmare... Or stupid engineer, you decide...

[Brent Gordon]

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
>
>