Chosen Solution
Hey I have an iMac 27” Late 2012. I didn’t use it for the last month or so, yesterday I tried to turn it on, and when I press on the power button, nothing happens (it doesn’t even try to start). I tried NVRAM/SMC reset, tried different cable, different outlet, but nothing helped. I removed the display (I’m familiar with process as I’ve done it in the past when I upgraded my SSD, it took approximately 5 minutes), I looked at the diagnostics LEDs and found that all LEDs are off. I removed the power cable from the back of the iMac, waited a few minutes, plugged it back, and LED #1 turned on for half a second and then turned off. My wife told me that there was a power outage earlier this week and every lamp in the house started flashing (on/off) for a few times when that occurred. I don’t know if that has anything to do with the iMac issue as it was turned off when that happened (but still connected to power). What do you think is defective? And what part needs to be changed? UPDATE: I replaced the power supply and it has been working perfectly for the past few days.
Sadly, this sounds like the power supply got damaged from the surge of the restoration of power (or lightning). You’ll need to replace it heres the needed part iMac Intel 27" (Late 2012-2020) Power Supply and here’s the IFIXIT guide you’ll need to follow iMac Intel 27" EMC 2546 Power Supply Replacement. I do recommend you get at least a good surge suppressor (not a cheap power strip that claims to be one) or better yet a proper UPS. You’ll also will want to check your house wiring making sure the outlet is properly wired and grounded as well as the house breaker panel to the grounding rod or metal water pipe leaving your basement.
