[time-nuts] hp5328A PSU stupidity...

[Douglas Wire - PUPCo Studios]

Hello and thank you all for chiming in on my topic; all excellent
suggestions. I have been “out” since I submitted that, so I just now was
able to sit down and read through the last days digests. This is probably
the 10th HP5328A that I have had to fix the PSU on, so it shouldn’t be
such uncharted territory! Funny thing about it; as I sort of eluded to and
am now seeing 100% is that virtually everything is shorted “dead” to
ground, making any path from where the transformer leads the voltages out
forward to a 0Ω reading - that is why this is such a PITA; I was and still
am having a hard time finding a starting point with ANYTHING that is not
shorted to ground… I pulled all of the fuses and forgot that still allowed
the 4500uF cap to see potential and had to listen to it sizzle. (How dumb
was that???) Luckily I have a bunch of spares here to replace it with. I am
guessing with how absolutely shorted out everything is, this is merely a
case of me not seeing the forest for the trees; as something shorting every
bit of the PSU shouldn’t be that hard to find, darn it! I am going to pull
the schematics and flow chart and go through everything one by one to try
and find the “end of the line” culprit (which there may be several in
this situation) that are allowing a freeway like short to ground
potential… I wanted to use one of the bench PSU’s too to unravel this,
but a quick run through with the 196 in the Ω range tells me all that will
happen is it will see the same short and current over limit will shut it
down; just as the fuses and everything else failed when I plugged the unit
in. Thanks for all of the suggestions. As mentioned, I have fixed nearly a
dozen of these and never run into one this out of whack; which is why I
posted. The offer to just swap for a working PSU board is tempting, but I
really cannot afford anything at the moment and I should have nearly all of
the components on this PSU laying around either in the parts bins or
available from a scavenger board… Thanks again everyone, I will keep
everyone up to date; it likely will be funny when I find the problem as
something tells me it has to be a pretty obvious issue to short everything
out together… It also looks as if someone has already swapped PSU boards
in this judging by the solder joints and such as well as the coloration of
the board is a slightly different color too…

 

Warm regards,

Douglas M. Wire, GED, FNA,