Well, it will look like everything is shorted to ground if some major power line on the PCB has a component that has gone really full sort. You will only find this out either by un-soldering it (eventually) or you use a high end ohmmeter that can measure really low ohms in 4-wire mode with a kelvin probe. I use a HP 3456A but I'm sure there are plenty of other instruments that fit the bill. Even a decent Fluke meter won't work to show you this sort of problem as there are shorts and very low resistance paths. When you can measure the resistance of a PCB track your up and ready for this.
Cheers, Steve 2009/9/11 Douglas Wire - PUPCo Studios <cont...@pupcostudios.com>: > 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, > > > > _______________________________________________ > 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. -- Steve Rooke - ZL3TUV & G8KVD A man with one clock knows what time it is; A man with two clocks is never quite sure. _______________________________________________ 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.
