Chosen Solution
iMac does not power ON Hi, I have a Power issue with my mid 2011 iMac. I’ve already opened it up. I have experience with repairing electronics, etc. But now i’m stuck. On the logic board ( Main board) : Diagnostic LEd no light, I measure 12v and 5v on the supply.
@djdanny if you have no LED light up you are having problems with the PSU. You said you tested it for 12V and 5V but are not telling us where and how you tested this. At this point I would consider starting by replacing the power supply and/or double check your connections etc.
I have the same issue, I only have led 1 and when i press the power button - led 1 shuts off. There is a little fan spin for a millisecond.
