Russ14

So if i disconnect the logic board from the power supply, all the voltages are there. when i plug it back in, the -2.1 volts disappear. Checked all the diodes and tested the capacitors with a capacitance meter, and power supply seems fine. Anyone know of any common fixes with this symptom? I'm sure I'm just gonna have to replace the system, but thought i'd throw this out there.