IBM 5155 Power supply schematics or info

Tony Duell ard at p850ug1.demon.co.uk
Wed Nov 9 19:01:56 CST 2005


> I have found the voltage under threshold isolating one by one the output of
> the four comparator (desoldering the pin) and there is two voltage out of
> range : +12V is 11V and -12V is 10V. In fact the two comparator of the two
> voltage, if connected, shut down the power supply.

Do you have anough load on the _+5V_ supply? Remember, these supplies 
regulate the 5V output (that's the one that's fed back to the error 
amplifier on the 3524 chip), and the other outputs follow along. If you 
don't give the 5V supply enough load, the supply doesn't have to 'work 
very hard', and the other outputs tend to be low.

Alos check the output capacitors. A dried up one will cause all sorts of 
problems.

-tony




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