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Ibm 5150 63.5w psu

J

joelgraff

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Joined
Jun 16, 2018
Messages
40
Location
Illinois, USA
I have a 63.5 W PSU I'm trying to troubleshoot and I was wondering if there were resources available for getting started. I've found a pieced-together schematic that seems to fit what I have, so that's a starting point.

Right now, I see it putting out 8V AC on the floppy power connectors and 3.25 vDC on three pins of one of the motherboard connectors. I know it's not designed to run properly without a load, so I can't really trust those readings, but I'd rather not hook it up to the original equipment in order to test it... :)

In any case pointers would be appreciated.
 
If it were me I'd just start by swapping out all the capacitors in the thing. There is pretty good chance that the issue is with one of them.
 
if it's leaking that much AC I'd start with the biggest cap in there, should be right near the mains input
 
How are you testing ? A digital multimeter ? Reason why I ask because you say 8 V AC. Does you meter differentiate between AC and DC ? You should be on DC setting.
 
Stone said:
It almost sounds like it would read correctly if you were to put a load on it.
Click to expand...


Well, I gave it a shot. I've stripped the motherboard of every socketed IC, and plugged in the connectors... and hooked up a floppy disk. From what I read, either one should be enough to load the PSU to get it to turn on.

The result - a popped cpactior on the motherboard and on the floppy disk drive card.

So I unhooked it and tested the harnesses again.

I saw voltages briefly before the powersupply (presumably) shut itself down due to no load detected. On P8, I saw it hit +5 and -5v on the appropriate pins. On P9, The +12 hit 9-ish volts, the -12 hit -6ish volts.

Sooo.. maybe it's ok. But I doubt it. All the same, a recapping may be all this needs after all.

Just wish there was a way to test it with enough load to feel confident about what it's doing.
 
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