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MNBassman
07-10-2008, 04:15 PM
During bootup my PC just powered down. No unusual noise or anything like that. Now it will not bootup or anything.

My first thought was the PSU had gone bad. I took it out and hooked it up to my old PC. The PSU in question is a 250W ASX 12V with 20-pin and 4-pin connectors. The motherboard of my old PC was made for the old ASXs with only one 20-pin connector. I tried it anyway, hooking up only the 20-pin to my old MB and the PC booted up fine. Molex connectors were putting out 5V and the 4-pin main connector was putting out 12V.

I'm assuming that means my PSU is okay which perhaps means I should be posting elsewhere, but I'm looking for the next step.

I tried shorting the soft power jumpers with no success. The only indication that there is power on the MB is the little green light next to the CPU and some low voltage readings from the power supply(max 3.8V). I read somewhere that my PSU should put out 5V even when powered down as long as it is plugged into the wall. Is that true? I don't get anywhere near that on any of the Molex connectors (max .25V).

Sooooooooooo.....what likely is my problem? Bad MB? Any other diagonostics I haven't mentioned that would be helpful?

david eaton
07-10-2008, 05:38 PM
A PSU will give 5V on the 5VSB rail only when connected to the mains. This provides power for the on/off switch. What voltages do you get on a molex. while switched on?

MNBassman
07-10-2008, 06:22 PM
When I connected the PSU to my old PC I was reading about 5V from the molex.

MNBassman
07-10-2008, 06:24 PM
btw....this PSU doesn't have an on/off switch on it so I suppose I can't test that without the PC running.

david eaton
07-12-2008, 05:18 PM
When I connected the PSU to my old PC I was reading about 5V from the molex.

There are two power rails on each Molex. 5V and 12V.The Red wire is 5Vand the yellow is the 12v

Are you getting both rails OK.