Model A1419 / Late 2012 / 2.9 & 3.2 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac13,2

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Apple STUMPED - iMac shuts off randomly, daily to multiple times/hour

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.

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This is usually indicative of a partially failing power supply.

iMac Intel 27" EMC 2546 Power Supply Replacement

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I've replaced the power supply and hope that has fixed it for good.

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@billymoon well is it working?

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Yes, it is working. Because the issue of the Mac shutting down sometimes took weeks or months to begin happening, it will be a while before I can 100% confirm that the power supply was the issue. But looks good so far! Thanks.

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Fantastic and you didn't have to pay through the nose to Apple ;-)

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And did this now solve the problem? I am having the exact jouney... :(

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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. https://support.apple.com/en-us/HT201295

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.

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Thanks for the tip. The very first guy who looked at it in VT said the same. I though taking it to Apple would be best, oops.

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I do still have a problem because i cant reset the SMC. My Mac, when trying to power on he has the black screen and makes just one 1 second of that opening noise but then it stops. If try it again it even doesnt make the sound and shuts down instantly. I tried to unplug the mac to restart the SMC but it has no effect. Need help

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Mine was solved by replacing the power supply.

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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.

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I am having the same problem. I immediately thought it was the power supply and took it to get it replaced. The geniuses could not replicate the problem and told me nothing was wrong. I brought it home. It worked flawlessly for about 6 weeks and then it starts cutting off again at least once a day. When it cuts off, I have to disconnect it from the outlet and wait 24 hours before it will cut back on. If I leave it in the outlet, it will not cut back on. (Its a 27 in iMac I've had since 2012).

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unplug from back of iMac count to 30 (not 20).

Press power button for 30 (not 20).

plug back in count to 30 (not 20)

then you can power up as normal or in safe mode or in diagnostic mode, etc.

Won't fix your intermitent shut down issues but I was able to boot for about another week.

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I had this exact same problem with my Late 2012 iMac 27" i7. Must be something particularly sensitive with the PSU on these models. Anyhow, I replaced the PSU with a new one ordered from Amazon (http://a.co/hXgDH0S) and so far so good! Upgraded the HDD to a 1TB SSD while I was in there!

So what causes these faulty PSUs on the iMac? I had no problems with this iMac until I started taking the unit home from work and plugging it into an outlet that was UNGROUNDED. I suspect that the fluctuations in current, be it sags or spikes, created this problem. I only did this under 10 times, but the damage was done. Word of caution to anyone who has a failing PSU on their iMac.... check to make sure that you are strictly using a grounded outlet (even better if you equip it with a UPS with AVR) once you get your faulty PSU replaced!

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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.

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Yes, you want a 3 pronged outlet which is correctly wired. I would also get a good surge suppressor or better a UPS!

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Yeah my problem was uncovered after I realized that in my 100 year old house, my three pronged outlet was actually just wired up without a ground wire. So It looked legit, but didn’t have the added protection that these sensitive electronic components require. Check your outlets especially in older homes!

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My 27” iMac has just started this random cutting out. May I just ask when you say changing the power supply do you just mean the power cord or something internal within the machine? I’ve already paid out for diagnostics when I first got this machine

(Few years back now) thinking hard drive was failing when it was just ram that didn’t like being in it. This has been my most problematic Mac ever

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In the original question yes, they replaced the power supply. iMac Intel 27" EMC 2546 Power Supply Replacement.

But before you go that far I would recommend replacing the cord first as well as make sure your house wiring is in good shape (grounding & not overloaded circuit). Next you might want to replace the power strip you have your system and peripherals with a good surge suppressor or better yet a UPS.

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Thanks Dan I will try everything before I need to open it up! I’d started with fuse, and changing power sockets so will try out everything that is suggested.

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Your shouldn't need to replace your house fuse. But you might want to figure out what circuit your system is on in the fuse panel and then make sure you've not put something thats power hungry on the same line. As an example: Window AC unit or electric heater.

You may want to replace the wall outlet (make sure you wire it correctly! Make sure the ground line is connected.

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Where do i start, my imac (2008) does the same (shutting down and back on again) i have changed the power chord and delved in and changed the power supply, that did nothing !!! I wiped the drive clean and a fresh install, nothing happened, so i put a new hard drive in, and still the problem keeps happening :( changed the ram, still no fix, so im only left with changing the logic baord !!! But after all that ive done, i dont think i can be bothered !!!

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so, well ......... I have just bought the logic board and I will be back with an update to tell you if it has fixed the problem

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so, the logic board arrived, I had to put the graphics card from the old board on to the one that arrived as it did not come with it and then installed the logic board and .................... it fixed the problem of randomly switching off and on, its running like a brand new iMac !!! I just wished I done that in the first place lol

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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.

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Billy Moon will be eternally grateful.
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