Old and new power supply -> trickle voltage LED off
My iMac late 2012 27" fails during the night in sleep mode. It doesn't go on at the morning. No Power on USB at all.
After some days of trying and waiting I decided to open the machine and none of the 4 diagnostic LEDs lit up. I could not measure any voltage. I measured mains cable -> OK. I measured inside the iMac between the mains connector socket and the mains connector on the power supply -> OK. I ordered a new power supply. The old was Delta the new is Liteon with same specs.
After replacement -> same problem again. No trickle voltage and no reaction at all.
What's going on here? What does the power supply (on some pins) need to deliver trickle voltage?
I try to find some technical information or shematics without any luck. I am an EE with all the measurement equipment and the soldering tools needed. But without more information I am at an dead end.
Is this a good question?