27 Oct
2005
27 Oct
'05
6:44 p.m.
I traced out scheamtics of the PSUs in all my
IBMs...
Great work ! Normally I trace out schematics only when I need to repaire its
and I cannot find any schematics on the net. How quickly do you need this? I am wondering if
handing a copy to a
friend at an HPCC meeting in a couple of weeks time would be soon enough.
No problem for the time, it's a hobby (great but hobby) non work :) Yes, and the control chip is on the
'output' side of the PSU, the drive
to the bases of the chopper transistors is transformer-coupled. There are
3 little daughterboards in there.
I have take a look at the circuit. It' similar to some off line converters
and other supplies, with control on the secondary side and not in the "live"
part of the switch mode. One is an inrush limiter and contains a
relay that shorts out a power resistor once the smoothing capacitors have
charged.
This work, I've tested. The 4 ohm resistor is shorted correctly by the relay Another contains the overcurrent protection
circuit, and, IIRC,
a 12V regulator. The last contains the overvoltage protection circuit
(the chips on that board are LM339 quad comparators).
I'm thinking about some protection circuit, because the switching try to
startup, for a time less then half second, and then stop. Now I can try to check il any protection become active during startup.
The SG3524 il correctly powered and try to fire up the switching
transistors, via the pulse transformer, but only for a short time.
Do you get any voltage appearing on any of the outputs? Even for that
half-second?
-tony