Chosen Solution
Is there and if so on wich pin a “power good” signal on the A1225 PSU ?
#1 LED ONLY indicates that the PSU is receiving trickle voltage, NOT that it is good or working.
bart koens here is the pinout for J600 and you’ll have a bit of trouble trying to figure out where to connect some external power. Yes, it does have PGood power sequencing on the board. Again it will be difficult to just applying power to the board.
I’d consider a new power supply instead.
iMac Intel 24" EMC 2134 and 2211 Diagnostic LED’s What are the onboard diagnostic LED’s telling you? Update (10/27/2018) LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty. Do any of the other LED’s light: If not your logic board has a problem.
