Chosen Solution
Hi so the iMac will not turn on, the screen stays black and there is no chime. I opened the iMac and noticed that LED #1 stays on but when I press the power button to try and turn on the iMac, LED #2 never turns on. I can hear the HDD spin up when I power on the iMac but no fans turn on. So I’m not sure if the PSU is bad or not. I tried to power on the iMac with everything put together, without an HDD, and without RAM, LED #2 never lit up. I ran a test on the RAM and HDD and both passed, so my question is if it is more likely to be the PSU being bad, the cable to the logic board being bad, the logic board being bad, or the CPU being bad. Thank you.
The power supply gets the worse of it! Yes, you need a new PSU. You should take some actions to help prevent killing the new PSU. First make sure your outlet is properly wired and the ground service is good. Go to the breaker panel and make sure the sound service from there is good. It should be connected to your water line main (metal) to the street and/or a grounding rod. Make sure you have not overloaded the circuit as well as make sure nothing heavy (heater, AC or compressor …) is on same circuit. Next you should have at least a good surge suppressor or better yet a good UPS! Here’s the needed part iMac Intel 27" (Late 2012-2020) Power Supply and heres the needed steps iMac Intel 27" EMC 2639 Power Supply Replacement
Dylan, I’ve done this repair 3 or 4 times now - and with those symptoms - it is most likely your power supply. It COULD be the logic board, but I have yet to see that happen. Any time your computer (or any appliance or amp) is not powering on, you should at least SUSPECT the PSU.
NOT BAD PSU - I have the same problem on an iMac 2011 27, only led one (1) is on and HDD spinning, nothing else (also power to HDD comes on immediately when plugging power to the computer. But I have another functional iMac exact same year and configurations. Putting the logic board from it in the problematic one and everything boots normally, fans ok, screen okey. That means that PSU, inverter board and all cables are ok, I have changed to a good GPU and new memory sticks on the faulty logic board but same problem and symptoms… So it has to be the logic board that is corrupt and broken… right?
