Good day folks. A former workmate of mine scrounged up this PSU from a client of us. He had a look at it and found a seized up fan which is presumably the main cause of failure. A couple of caps had bulged on the secondary, so it seemed like an easy fix. He replaced them and today I had the honor of doing the test run with him. We attached an ATX tester to its output and plugged it in: it's not quite there yet. While the supply did technically fire up with no pops or fireworks, it's got a couple of issues. The most prominent one is this "ringing" or rather crackling sound it's making (sound, just like scent, is one of the toughest things to explain in words sadly ). It's pretty loud and we were afraid something might actually pop. We decided to keep it plugged in anyway, at least to check up on our tester. Ironically, all the rails are up and in spec (no way to check ripple on them though), but then we ran into the second issue: 0ms on PG....the bane of my existence, since to this day I cannot work out a definite answer as to why some ATX supplies do this !
There's only two chips on this thing: the combined PFC/PWM IC (a CM6805)and the supervisor IC on the secondary, a ST9S313 for which I'm having trouble finding a datasheet....
First, the squealing is the more concerning issue, so I thought I should focus on it first...what could be causing this ? There could still be a bad cap somewhere, as my colleague only replaced the visibly damaged ones...might be a good idea to recap the whole thing (not sure if it's worth saving though - looks decent and fixable enough). What else could get damaged to cause this noise ? The noise is only present when the supply is "on", so it's not caused by the 5VSB circuit. Haven't tried loading the supply yet to see how or IF the noise is affected in any way. Most likely caused by the main transformer.
The 0ms PG issue: bad supervisor IC ? Perhaps other similar cases you might've come across ? Cheers guys.
There's only two chips on this thing: the combined PFC/PWM IC (a CM6805)and the supervisor IC on the secondary, a ST9S313 for which I'm having trouble finding a datasheet....
First, the squealing is the more concerning issue, so I thought I should focus on it first...what could be causing this ? There could still be a bad cap somewhere, as my colleague only replaced the visibly damaged ones...might be a good idea to recap the whole thing (not sure if it's worth saving though - looks decent and fixable enough). What else could get damaged to cause this noise ? The noise is only present when the supply is "on", so it's not caused by the 5VSB circuit. Haven't tried loading the supply yet to see how or IF the noise is affected in any way. Most likely caused by the main transformer.
The 0ms PG issue: bad supervisor IC ? Perhaps other similar cases you might've come across ? Cheers guys.
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