Hi ! I'm tryin' to service an IBM Server 325 PSU, suddenly dead. I checked all capacitors, diodes and other stuff for shorts. I put a paper clip connecting the power on pin with gnd. The rectified voltage (generated by a separate board) reaches a primary stage, with discrete components and three ICs TOP200YAI - Three-terminal Off-line PWM Switch LM393P - as usual UC3843AN - Current Mode PWM Controller CQY80NG - Optocoupler and two transformers.
Well, from this stage exits nothing, with or w/o the paper clip. My experience on switching PSUs is very limited. The PowerOn signal doesn't reach directly the first stage but a custom made riser card, so the fault could be elsewhere. Any hints on where to begin lookin'?
As a last resort, since the output voltages are the same of a standard ATX, only with different connectors, I could swap them and use a "normal" ATX.
But I'd give a try, it could be a useful experience...