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iMac 27" 3.4 GHz i7 (Late 2012) This iMac was my father’s and began having this issue last summer. It will simply power off completely at random - sometimes being able to be powered back on immediately, sometimes not turning on for an hour. This problem persisted for months and grew more frequent until it was happening several times a day. Rather than try to deal with it over long distance, I had him buy a new iMac and took the old one with me to NYC. Took to Apple, who found nothing wrong. I reformatted the drive, did a new install and step up with new software in a completely new environment - I did NOT restore from any user or backup. Within a week the Mac started shutting off again. I brought it to Apple again. They kept the machine this time and ran diagnostic over days but could not get it to repeat shut down in their possession and insisted it was a software issue. We rebuilt the machine once more and tried again. This time it worked for a few months before starting to shut down occasionally again. At first just every few days, then nearly daily (oddly often around the same time in the afternoon), and then multiple times a day. I brought back to Apple once more and eventually spoke on the phone with a master tech somewhere in the Midwest who also thought the “Geniuses” must be missing something and gave them more stressful test to try. Again, they can’t get the machine to replicate the problem. This machine has been rebuilt several times.This machine has been in two completely different environments, with different sets of software from different sources.I have swapped power cords. I have tried different surge protectors and outlets. I am at a loss and Apple will not tell me anything is wrong to replace. Except for the shutting off, this still remains one of the fastest Macs I’ve used from probably 15 different 27" models from 2010 - late 2015. Any suggestions? Thank you very much.
This is usually indicative of a partially failing power supply. iMac Intel 27" EMC 2546 Power Supply Replacement
Since this is a basic first step to resolve power issues, I would imagine that the Apple techs have reset the SMC, but if not try this. How to reset the System Management Controller (SMC) on your Mac I once had a similar problem with an iBook, many years ago. Resetting the SMC would work for a period of time and then the powering off would happen again. I discovered eventually that it was a logic board/processor issue.
I had the same issue with my iMac 27" late 2012 model, random shut down, pull the power cord, wait, plug back in, runs fine or a while, repeat every few days until it became daily. I replaced the power supply board and it’s all good… Only a few days so far with no problems for a REAL proof, but it was shutting down daily. Key things? I think the fact that I had to unplug after every shut down to be able to restart was a solid clue that it wasn’t a software issue. As Greg Blair pointed out, I ALSO have UNGROUNDED power to my machine. Maybe that is what kills the board? Just mentioning it here in case that turns out to be a common clue as well.
Had the same issue after heavy CAD use of my iMac (same machine, late 2012 3.4 GHz) for some hours, and it continued to happen. After I found this thread, I decided to check the outlet and turns out it was faulty, grounding wire was missing on the back side! Plugged the iMac into a good grounded outlet and it’s been running fine since.
After speaking to an IT guy who was having the same problem, I replaced the power cord and am no longer having problems. I also turn my iMac off at night and disconnect it from the outlet.
My 2104 iMac have same issue too! I’ve had to move to a country with 110 V, before my iMac have never had this problem under 220 V power of my home country. So I’ll try to connect at 110 V to 220 V Transformer. That fixed the problem!
I had the same problem with a 27 inch 2013 model. Since I don’ t live in the usa I could not bring it to the Apple store. I’ ve tried everything. Changing sockets, buying UPS, disconnecting everything and connecting them back 1 by 1. Had a IT friend look at it and at his house everything worked perfect. Brought it back home and same problem again. Suddenly the battery of the keyboard was dying very quickly. I had to change batteries every 2 weeks. After the 2nd time I was so fed up with batteries that I just replaced the wireless Apple keyboard with a generic non Apple wired keyboard. I was thinking about buying a new MAC. So glad I did not do that. The MAC has been working fine since that day, now almost 3 months ago.
I brought my late 2012 iMac to Apple today and it powered down twice while I was there. Power supply was one of the possibilties they cited. Will let you know in “5-7 days” what they find out. UPDATE They replaced the power supply - just got it back today.
I know this is an old thread but I’d like to share my experience. I had a very similar problem where my iMac would shut off randomly. Turns out the RAM was bad, I replaced the RAM and have been stress testing the machine for four hours using the “yes > /dev/null command and GPuTest. So far so good. Be sure to try removing RAM sticks as part of your trouble shooting process. By the way, the RAM is Crucial 1333MHz 4GB x 4 sticks.
My mid-2017 is doing this same thing. I bought it brand new in May 2019 from the Apple store. I had no idea I was buying a 2017 model in 2019, which is a separate point of contention. So, my apartment is in a 100 year old building. There are no grounded outlets - they are all ungrounded and I can’t afford thousands of dollars to rewire someone else’s building. I do use a surge protector. Is there anything else I should be doing? Should I unplug and shut down every single night? Thank you in advance. It’s aggravating having a brand new computer with issues. My powerbook last for 8 years without incident. Thanks again~
Hi I have a similar Issue, I’m in the UK so don’t think its a grounding issue… Randomly turns off sometimes as soon as trying to log in, some times 40 minutes after logging in, other times 24 hours. It is not a complete shut down it is just completely losing power. I have an iMac (Retina 5K, 27-inch, Mid 2015) and just wondering for any advise out there? I’ve looked at the process into replacing the power supply unit - the issue is I have a small crack in the glass on the screen - luckily this hasn’t effected the display…. Is this likely to break or damage further taking this to pieces? Any help would be greatly appreciated. Thanks
Bought 2012 iMac 27” from Indiana University surplus store. Worked fine and what has been described on this thread is EXACTLY what mine did…randomly shutting off. Unplug it and sometimes 30 seconds, sometimes 30 min plug it in and starts up again…was doing it several times a day making the computer unusable. I did vacuum out vent to remove any dust as has been described and that worked with no shutdowns for maybe 2 months, then started to do it again…vacuumed out again and that sort of worked for a month. Took it into local MAC repair guys and they said they checked out PSU and they said everything was checking out okay, so they assumed board was bad. Too old to make it worthwhile to fix now, but screen is perfect and love it otherwise. Just asking here…is the consensus just to replace the PSU and see what happens? Otherwise, it has zero value in trade-in, and isn’t heavy enough to be a boat anchor.
I have the same machine, 13,2 I7 32GB 27” late 2012 and same problem. No one mentions it but when I switch to bootcamped Windows 10 it works fine. For example, recently when it started shutting down a couple of minutes into starting MacOS, I switched to Windows and kept it running there for a couple of days without an issue.
