Hello,
Here is my problem.
I have ...
power supply A at the 4 pin molex plug with no load I have 5.13 vdc and 11.66 vdc with a hd load I have 4.9 vdc and 11.5 vdc
power supply B at the 4 pin molex plug with no load I have 5.03 vdc and 12.18 vdc with a hd load I have 4.5 vdc and 12.9 vdc
For some reason which is evading me the pc will boot to the hd when using power supply A but not when using power supply B
I am not an expert and the only explanation I can come up with is the drop of the 5 vdc pin to 4.5 vdc on power supply B is not providing enough voltage to run the hd.
Am I correct in this line of thinking or is there another explanation?

 

I will guess that the problem is on the capacitor related with the 5V power supply, please check the filter capacitors has any bulging or the capacitor liquid was dry or ooze out?

Probably the capacitor needs to unsolder from pcb and measuring the values of capacitance.

 

Scott,
That is what I feared. I took the PS apart and on closer inspection 3 or 4 of the capacitors have bulged.
Thank you the advice and insight
Bill

 

Some capacitors already bulged and those are what you can see, but some capacitor liquid was dried, it will causes the values of capacitance too less, but you can't see it as bulged, so you need to unsolder them from pcb and using capacitor meter to do the measuring.

Some technicians may unsolder all of the old capacitors and replace them with the new capacitors.