IBM 5155 Power supply schematics or info

Tony Duell ard at
Mon Nov 7 18:47:35 CST 2005

> > 2) It's shut down. The shutdown pin is driven from the SCR CR11 on the
> > 1144-01E PCB. That takes inputs from the current sense circuit and the
> > overvoltage shutdown. Since you say that the shutdown pin is not asserted
> > (do check this at the 'other' side of R11, 6k8), I think this is not the
> > problem weeither.
> I was in error, the 3524 is shutdowned (lessical correct? :))
> After a short time (during this outputs are available) the signal on R11
> goes high, blocking 3524
> Now I try to understand if is current overload or voltage protection circuit
> that become active.

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.


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