Chosen Solution
Hi there, Since two years ago I’m having random shutdown problems with my iMac. I’ve tried a lot of things but the last thing, because I think it can be a heat problem, was replace the HDD for a solid disc, it cools down the machine but randomly I’ve still having shutdown problems. The main issue to me is that I can’t reproduce the shutdowns so it’s frustrating to give the machine to a technician listen from him the machine is fine… Recently I’ve noticed that I can’t reset the NVRAN (using CMD+OPT+P+R) because when I’m doing it the Mac wont start again and I’m wondering if that fact maybe can help for a diagnosis. What do you think? Thanks in advance!
I’m thinking your real issue is a bad power supply and/or poor power in your home. I would first make sure your outlet you are using for your computer is 20 Amp (120-US) and you only have a your computer gear connected on that power circuit. I would recommend getting a good fill-in UPS if you note your lights flicker as thats a good sign of poor power. Even still you might want to ask your power supplier for a power meter for a week so you can see how your buildings power is. I would also make sure the outlet is properly grounded and back at the breaker panel make sure the ground service is properly grounded (check the ground line and the ground point its self!) Only after checking your power service would I dig deeper into your computer. I would swap out the power cord with a known good one. sometimes the simplest solution is forgotten! I would reduce what you have running to make sure you aren’t mistaking a software issue as a hardware one. Then I would look at the diagnostic LED’s on the logic board while not ideal you can get an internal display cable extension hopefully you can catch the event. Otherwise I would just replace the power supply. Update (02/01/2018) Here’s the needed part: iMac 27" Power Supply, 300W, Late 2012/13 and here’s the IFIXIT guide you’ll need to follow: iMac Intel 27" EMC 2546 Power Supply Replacement
