Model A1419 / Late 2012 / 2.9 & 3.2 GHz Core i5 or 3.4 GHz Core i7 Processor

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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.

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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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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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Billy Moon will be eternally grateful.
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