Hello, I have a Compaq sr1650nx desktop. The unit quit working and the power supply light blinks. I have isolated the problem to the 4 Pin atx12v1 connector. With that connector removed the power supply will power up, run the fans and one of my dvd drive goes through its paces. As soon as I plug that connector in, the unit, fans and pwr sply shut down and the light starts blinking. I read where this connector powers up the cpu (an AMD 3500+); is this so and do I need a new cpu. Or are there other checks I wshould make?
Or more likely, a new PSU. If the CPU is fried, the onboard power regulator that converts the 12 volts from the PSU into whatever the CPU needs should crowbar (that's techspeak for "electronically shutdown when it detects a shorted CPU) before the PSU does the same thing.
Try to borrow a known good PSU. If you cannot do that, get a DMM to measure the voltages. Measure between the colored wires and either ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.
The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.
You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.