Now all I need to do is fix my out of tolerance
MicroVAX 3100 Model 95 PSU
I think the first thing you need to do with that one is to find out what
the output voltages should be _and which pins they're on_ so you can see
just what it is, or is not, doing.
and a PSU in a VAXstation 4000 VLC that
"tweets" on and off. One of these
A 'tweeting' PSU is generaly one that is trying to start up, detecting a
problem, and then hutting down again, Possibly due to bad capcitors
(often, but not always, on the output side. Maybe an overvoltage problem
(so the crowbar circuit is tripping). Possibly a problem with the
shutdown circuitry itslef (there isn't really a problem, but the shutdown
is being triggered anyway) -- but whateveryou do, don't be tempted to
disable protection circuits. I did once, when younger and more foolish,
and ended up with transistors blown apart, metled track, and many other
things to repair.
days I might actually start to understand PSUs :-)
I've yet to fidn a really good book,web page on this. The way I learnt
was to read the scheamtics and circuit descriptions of every docuemtned
PSU I could find, to read all the data shets on the control ICs, etc.
It is very difficult in my experience to repair an SMPSU without a
schematic. You may be lucky and spot the bad component, but most of the
time you need to work through the schematic logically. Alas the
scheamtics of most modern-ish PSUs are unobtainable. I gnerally resort to
tracing out the full schematic, then interpretting it, and only then
starting to fix the thing.