IBM 5155 Power supply schematics or info

Whatever you do, don't try disabling any of the shutdown circuits.... The results can be spectacular and expensive. There are 3 possible shutdowns (undervolage, overvoltage, overcurrent) which are diode-ORed together onto the gate of CR11 (the shutdown SCR I mentioned in the last message). I would look at the 1068-01A voltage limit PCB. There are 2 transistors on that board. Q3002 is cut off (collector goes high) if there's an overvoltage. Q3001 is cut off if there's an undervoltage for too long (R3024 and C0001 act as a delay on this signal). 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. -tony