IBM 5155 Power supply schematics or info

[Tony Duell]

> 
> > I think I would check C3001, in case it's shutting the PSU down before
> > it's properly started. Then look at the collectors of Q3002 to see if the
> > thing is detecting an overvoltage.
> 
> The under voltage protection is always active :(

Ah...

> When power is applied, the collector of Q3001 goes high (about 4.5V)

Well, it shoud be until the PSU gets going :-). 

> immediatly, after about 0.5 seconds, the SCR is fired and the power supply
> enter in protection mode.

I presume that delay is that 47uF capacitor charging up. So that's probably
not defective.

> During the short time of outputs presents, I have check the value (with
> scope, multimeter in not enough fast) but they are of the correct value (+5,
> +12, -5, -12) but I ignore the tolerance of the under voltage protection.
> 
> Maybe IC3001 or IC3002 defective ?

Or the transistor is open-circuit?

Still, you're now down to one simple-ish stage that presumably you can 
debug. 

Incidentally, I should get a copy of the schematics to Dave at the 
weekend for scanning.

-tony