Chosen Solution
I have an late 2012 iMAC that does not power up. It was fine the day before and didn’t do anything a day later. When I connect the power cord I can hear a slight sound. Thereafter nothing happens when I press the power bottom. Pressing it for longer time does not help either nor does it help to reset the SMC. The shift caps led on the keyboard is not working. I took off the screen and connected the power cord: only one LED (lowest) on the logic board is on (the screen is not connected). After pressing the power switch this one LED turns off as well. I removed the power supply and connected it via the iMAC to the mains. Mains connection is ok. I get 12V and -12 V on some of the pins of the connector the logic board. I also can’t see or smell any blown up capacitors. Any ideas? Update (07/17/2018) Hi, tried a new power supply which was difficult to get - so it took some time. Plugged it in and the situation is the same:
- When I connect the plug to the mains the lowest LED is on.
- Once I press the power button of the iMAC this LED goes off (all off).
- I have to disconnect the mains and wait for a short moment and then after connecting the iMAC again to the mains the lowest LED is on again.
- If I do the last step too fast the lowest LED stays off. Any other ideas what to try? Best Frank
I would say your power supply is still the issue. Here’s the IFIXIT guide: iMac Intel 27" EMC 2546 Power Supply Replacement and here’s the needed part: iMac Intel 27" (Late 2012-2020) Power Supply
