Chosen Solution
Hello guys, I have a dead iMac with no LED on at all. Logic board ID 820-3588, power supply tested OK power input to power supply OK tested with new known good power supply but still no 12v present on logic board. any advice for this case? Update : Tested with normal board and works fine. so the problem is the logic board. Power supply output 0v with original logic board
Where are you testing for 12V? That might help determine exactly what’s going on. It’s possible the connector for the power supply is at fault. The first LED is reliant on 12 volts insomuch as all other voltages are derived from it. The first LED is actually lights from PP3V3_S5, which still leaves some other things in the logic board chain that could be at fault even beyond the 12V.
