https://discussions.apple.com/thread/2171912?start=0&tstart=0
Tried the trick with the power supply unplugged from motherboard and drives. Still won't turn on. I opened it and only found one fuse (checked good) and no obvious issue like bulging cap or burn resistor. Only one obvious relay and it's wired with coil on 12v side and N.O. contact across hot wire connecting to second power port for monitor or peripheral, doesn't do anything on the main power in. 4 individual PCB boards all soldered together and lots of parts makes this a bit hard to troubleshoot. I'm not de-soldering and checking every resistors, every diode, and replacing all 40 or so electrolytic caps. There's about a dozen transistors and regulators which won't be easy to test if they aren't plain vanilla transistor (don't have anything to test for FET, regulator, switching IC, etc)
Tried the trick with the power supply unplugged from motherboard and drives. Still won't turn on. I opened it and only found one fuse (checked good) and no obvious issue like bulging cap or burn resistor. Only one obvious relay and it's wired with coil on 12v side and N.O. contact across hot wire connecting to second power port for monitor or peripheral, doesn't do anything on the main power in. 4 individual PCB boards all soldered together and lots of parts makes this a bit hard to troubleshoot. I'm not de-soldering and checking every resistors, every diode, and replacing all 40 or so electrolytic caps. There's about a dozen transistors and regulators which won't be easy to test if they aren't plain vanilla transistor (don't have anything to test for FET, regulator, switching IC, etc)