IBM PX and XT Power supplies

[Tony Duell]

> 
> IBM never released the schematics, even to internal IBM sites wanting them.

Maybe because IBM never had them (after all, the PSUs were not designed 
by IBM), or because there were so many versions.

As an aside, the TRS80 M3 and M4 used Astec PSU boards. ASTEC did not 
normally release schematics, but Radio Shack sold techncial manuals for 
these machines. The PSU schematic in there was clearly reverse-engineered 
by Radio Shack, and is almost hilarious. It bears little relation to any 
of the PSUs I've seen in these machines (there are at least 2, 115V only 
and 115/230V), or indeed to any working SMPSU.

> 
> Early on, we learned that there was a optoisolator that often died.
> 
> There WERE aftermarket schematics available for about $40 in the mid-80's; 
> I don't
> think I have any?? A friend still at IBM may.. I'll ask when I see him.

The PC, PC/XT and PortablePC supplies are all very similar designs. No, 
you can't intercahnge them, but if you had a schematic for one, you could 
find your way round any of them

I've traced out schecmatics for the ones in my machines. I've offered to 
get the PortablePC one scanned. Do you want me to see if I can get the 
others done sometime.

-tony