IBM 5155 Power supply schematics or info

[Tony Duell]

> 
> > I hav ereverse-engineered this unit (there is no official schematic in
> > any of the manuals).
> 
> Great! I have plan to do the same, in nobody has already done :)

I traced out scheamtics of the PSUs in all my IBMs...

> 
> > Alas I have no scanner, so as yet there are no schematics in eelctronic
> > form. But I will see if something can be done.
> 
> Thanks, thanks and more thanks !

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.

> 
> > I've never had to repair one, but from what I remember it is a fairly
> > conventional design.
> 
> In the past I've repaired two, but with very simple damage, one with the
> output capacitors die and another with the auxiliary little transformer with
> primary coil interrupted.
> The circuit work around an old pwm controller, SG3524 of SGS Thomson.

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. One is an inrush limiter and contains a 
relay that shorts out a power resistor once the smoothing capacitors have 
charged. 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).

Waht I would do next is : 

Check you're getting about 350V DC across the mains smoothing capacitors 
(2 electrolytics in series)

CHeck you're getting power to the 3524 (if not, troubleshoot the circuit 
round that little transformer you mentioned)

Check that the 3524 is oscillating.

-tony