i have a psu in system that is not working, i noticed that a yellow light on back of psu is off normally but when i unplug 24pin connector from m/b the light comes on - tried this on other m/bs and it's the same.
tried a psu tester, the psu fan runs etc, and only light not coming on is -5v.
Personally I've never had a psu with lights on the back. However it seems that the yellow light would indicate if something is wrong (atx connector uplugged), so that is normal right? Do you have the manual? You can look it up.
Seems logical to get another psu and try it.
tried another power supply and it worked ok but wanted to make sure the problem could not be rectified on old psu - didn't want to throw good psu away....
ummm-if its a good psu it wouldnt be broken-but if you want to fix it, you are good at soldering, etc, then open it up and look for bulding or leaking capacitors.
a good site for more info on that is badcaps.net.