A capacitor in the power supply may be blown. Try swapping out the power supply. You could take the power supply apart and do a visual inspection. If you see a bulging capacitor or two, that might be your problem right there.
Cables and connections are all checked in triplicate, but, I can also check power supply voltages. (Fluke 8060A meter)
Thing is, most everything that should get warm does get warm, about as expected. But an individual rail somewhere could be down...