Re: Power distribution panel problem

[brian whatcott <inet@INTELLISYS.NET>]

At 14:27 3/23/01 -0600, you wrote:
> Our physics lab has a central panel that distributes regulated DC to the lab
> benches.  It was built for us by Hampden Engineering in about 1972 and has
> worked perfectly until today.  Now suddenly the output of one of the 15-volt
> regulated power supplies will only go up to about half a volt when the
> variac is turned up all the way (with no load), as indicated by its own
> meter.
>
> Before starting to pursue this problem, I'm wondering if any of you have had
> experience troubleshooting or repairing such devices and could offer any
> suggestions.
> ______________________________________
> Fred Lemmerhirt
> Waubonsee Community College
> Sugar Grove, Illinois
> flemmerhirt@mail.wcc.cc.il.us <mailto:flemmerhirt@mail.wcc.cc.il.us>
> http://chat.wcc.cc.il.us/~flemmerh/physics.html
> <http://chat.wcc.cc.il.us/~flemmerh/physics.html>


The scenario sounds interesting. There is something of a conceptual
 conflict. There are regulated 15V DC supplies. There is a variac.
 This could be a soft start for fixed DC supplies, or more intriguing,
there could be regulated DC supplies, made variable by means of a variac.
Only one 15 V DC supply is affected, I think.
It might be fed by AC, rectified AC or roughly smoothed DC.
If one sees a difference at the faulty supply's input cf the other
15 V DC supplies' inputs, then the problem is localized.
A rectifier, a smoothing cap, and a failed pass transistor are
favored culprits. Electrolytic caps of this venerable age
are particularly suspect.


brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!