I'm pretty confident that the PSU is bad in this computer, but I want to understand what my multimeter is telling me. With the PSU plugged into the wall only, the multimeter says that pin 9 is a little over 5 volts. When I plug the P1 connector into the motherboard and test pin 9 again, the voltage is now between 3.70 and 3.90 volts.
The computer will not power on at all. I put in a different PSU that I knew worked and it powered on just fine.
My question is why would the voltage be lower on pin 9 when the P1 connector is plugged into the motherboard? Is that normal (or a good sign that the PSU is bad)?