IBM never released the schematics, even to internal IBM sites wanting them.
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 XT versions were a lot more reliable; I have 8 XT's that get turned on
only once or twice a year, now, and I've never lost a power supply or
system board.
Regards, Terry King ...On The Mediterranean in Carthage, Tunisia
terry at terryking.us