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모델 A1419 / Late 2012 / 2.9 & 3.2 GHz Core i5 또는 3.4 GHz Core i7 프로세서, 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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I replaced the Power Supply for 125.00. Works great now. Apple has been no help in this issue.

I’ve been dealing with the same for 5 years. Apple never finds anything wrong, get it back, still shuts down. Now they are whining about us requesting a new computer, on their dime, because of the age of the computer. My argument is that it has done this since 11 months old, now about 5, and I have almost never been able to use it during that time. They deny they have ever heard anything like this, yet I can find it all over Internet forums. I’m so frustrated! I’ll be purchasing some kind of crap laptop this coming week. I need a computer. But I’m done with apple products. (Even 3 of our 5 iPhones do the same thing).

I had this same problem for the better part of 9 months (sometimes I'd get 5 shutdowns in an hour, and other times my iMac wouldn't shut down for days/weeks). Nobody on the forums I frequent had any solid ideas/suggestions about what might be causing this (I heard errant programs, kernel panics, etc., but none of those seemed to be the case).

Then I happened upon this article; lots of similarities to the problems I was encountering with this very specific iMac model.

I replaced the Power Supply about 3 weeks ago, and haven't had one shutdown since. At this point, I'm going to cast my vote for this being the problem/solution.

Word of caution: when peeling off the old adhesive from the back edges of the screen, don't be too aggressive. I applied a little too much pressure with my plastic widget/tool (don't know what it's really called), and wound up scraping off a little bit of the black paint on the backside of the screen, which leaves the glass bare (and noticeable when the machine is put back together).

I had this problem and lived with it for about 3 months - I had the power supply replaced and it corrected the problem.

Exact same problem. I have taken it in 3 times now and they cannot get it to do it. I will be working in illustrator or indesign and it just shuts down.

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선택된 해법

This is usually indicative of a partially failing power supply.

iMac Intel 27" EMC 2546 Power Supply Replacement

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댓글 32개:

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

@billymoon well is it working?

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.

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

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. 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.

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댓글 7개:

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.

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

Mine was solved by replacing the power supply.

I just checked my outlet and it read REVERSE POLARITY, so I switched my iMac 13,2 to another outlet with a GROUNDED extension cord. My iMac was shutting down like in OP's description. I'll report back if that fixed the problem, to help others.

I've taken my refurbished Mac 27" w/3 TB back to an Apply subsidiary (MacMedia) twice. They couldn't replicate the problem but gave me another machine. Same thing. There is obviously a problem with it. Why won't Apply acknowledge?

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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 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!

Update (05/07/2018)

I still contend that the random shut downs are due to faulty power supply unit inside iMac.

Once these get tweaked by sags or surges in current from your electrical or ungrounded outlet the damage has been done!

I HAVE had a faulty logic board on a previous machine but it was exhibiting different behavior.

In my experience, when the logic board fails you see strange colors and picture on screen. When the machine just shuts off, I believe that is not a logic board issue and rather a PSU problem.

Apple is no help in getting this resolved.

Thanks to the iFixit guides and a little online shopping I fixed the issue 100% myself (and I’m no hardware guru, I’ve only opened up my iMac once).

Check out these attached pics of a failing logic board and you will see that that is a separate issue. If your Mac is randomly going black, shutting down and the only way to hopefully power it back on is after you leave it unplugged for a few minutes.. You, my friend have a faulty power supply!

Block Image

Block Image

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Grounding & power fluctuations will kill any computer!

Yes! you need to get your outlet fixed as well as make sure the breaker panel ground service is properly grounded and the ground point is in good shape (over time it tends to degrade).

You should have all of your peripheral devices on surge suppressors as a minimum. Or better yet should get a good UPS if you are seeing flickering lights or have brownouts.

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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!

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!

I have the very same issue. And the partial solution is the same too - power off the mac, remove the cord, wait a bit and start up. I've standard EU outlet though with proper ground.

What is weird is that this issue occurs during summer season, so when the temperature in the room is higher. I was suspecting that mac is maybe overheating.

I checked the logs and was not able to find anything pointing out to the overheating though. Actually, it seems the shutdown is very sudden leaving osx without any chance to write anything.

I started having this issue last year. I opened up my mac, cleaned up, checked all the components but didn't find anything obvious. I've decided not to use the adhesive strips on display but rather used the duct tape. I actually like the look ;) And as I also had to repair the crappy stand I think it's best to be able to open it any time.

New PSU seems a bit pricey for this old machine. I'd like to know where the problem is but as it takes time for problem to show and it's hard to reproduce I guess there's not much else to do ..

I hope you fixed your homes wiring too! If you have missing or a bad ground that will damage the power supply.

Make sure the breaker/fuse panel ground is also in good shape! And use surge suppressors for your system and peripherals.

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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.

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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).

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.

Sounds like you have building (home) power issues!

Check your outlet is properly grounded and the breaker panel to ground is in good shape. You likely need a good UPS as well.

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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!

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Your power supply has in fact two circuits one for 120 volts and the other 220 volts. So your 120 circuit is bad! You still need a new power supply to fix this correctly. The cause was bad power! Do make sure to get a surge suppressor or better yet a UPS.

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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.

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I went with the generic non-Apple too and problems ceased. I am four hours distant from an Apple store.

I'm confused - was the problem the keyboard then??

@shannonw - Not likely! Power is the root issue. These are USB or BT connected and have no direct issue with system other than the control (key entry) and this series doesn't have a keyboard power switch.

Either the power supply and/or the power entering the home is not stable and/or the physical ground and the outlets ground are not properly setup so the system is not grounded!

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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.


They replaced the power supply - just got it back today.

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@homerfrizzell - did it work for you? Any more shut downs? I'm having the same problem for about 6 months now...

@hervoa - no shut downs since I got it back a week ago. I think the power supply was the culprit.

Good for you! I just dropped my imac at an apple store to change the power supply. Here goes $200... :(

I finally decided to drop it at an apple store. They kept it for 2 weeks and of course couldn't reproduce the shut down. I told them about the potential issue with the power supply - that i was ready to change. They checked every components (...so that they told me) but couldn't find any faulty hardware. So they basically didn't do anything - only cleaned it up, as dust was building up in there. Anyway, just got it back a few days ago. No crash yet....but still, Apple has to be aware about this issue. I even showed them some videos on youtube, showing the shut down!! they can't ignore this one forever...on a $3K box!!!

The newer Thin Series 2012 onwards are more sensitive to power issues! Get someone to check your buildings/house wiring making sure the outlet is properly wired and has a good ground. You may want to get a good UPS.

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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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Ok had the same problems like everyone I change the power supply and replaced the memory.

I also changed the power cable and now have the system plug into its owns surge protector

It’s was still shutting off then I went back and l replaced the memory again and now it has not randomly shut off in weeks.

I think you'll find the real issue is your building/house power is not stable. Time for a UPS!

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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~

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Then you should get the owner of the building to do the rewiring. If the building has ungrounded outlets that allow for plugs with PE to be plugged in, that's probably illegal.

I don't know where you live, but in most places there's distinct shapes for plugs/sockets with and without PE (In the US, that would be three-prong vs. two-prong), to ensure devices that require grounding can't be plugged into an ungrounded outlet.

Your old powerbook's power supply doesn't require grounding, that's why it comes with a two-prong plug. Same with Mac mini – no grounding required.

Using any electrical device that requires PE with an ungrounded outlet is not only highly dangerous and irresponsible, but might also be illegal.

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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.


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Grounding is only one issue, you likely have surges or dropouts. Best to get a good UPS.

Small cracks in glass can grow! Opening the system could stress the glass so be careful as you may sendup needing a new display.

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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.

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댓글 7개:

I have that iMac model and when I took it to be tested they told me the power supply was “fine” also. So, I decided to buy one myself and get it installed, rather than buy a whole new computer. It’s been about a year or so, and I haven’t had that issue since. So I’d say it’s worth a shot.

Over the years I tried almost everything, first thought it was an issue with office as it tended to shut off when I was in excel ,it might be usb driver issues So ran it with nothing plugged in, replaced hard drive with ssd, swapped ram in case it was fault , after last big shutdown i got PSu replaced then decided to replace mother board, a week later it started all over again.

Since then I’ve taken to not letting it sleep. Rather I turn it on when I need it and off as soon as I’m done with it that have nipped it in bud for now.

I have a wacom cintiq that backlight stop working ... but if you leave it unplugged for a week it will work again talking to my electronic engineer friends we have decided its an issue with capacitors not discharging enough so not charging and having too low boost to start tubes ... I’m gonna just guess something similar with imac. this doesn’t make tons of sense .. but turning it on and off and not letting it sleep seems to help so far ( its been 6months)

One thing I haven’t tried is something i read on the webs years ago when this first started. It was suggested this was actually an issue with the physical on/off button at back and if you pulled it Or replaced it the issue would go away .

No tech personI’ve talked to said this made any sense so I have never tried it.

Have you checked your wall outlet?

For me a faulty outlet (missing PE) was causing the issue, and plugging my iMac into a properly grounded outlet solved it for good.

Might also explain why your PSU checked out fine at the repair shop.

I too had a Mac with the same problems, replaced the PCU and never had the problem again. It’s still in use.

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My 27” late 2015 having this problem right now. after read all the comment above ill start the trouble shooting by replacing the thirtparty RAM ( Hyperx) to original Apple RAM

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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.

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I said mine has the "same problem" but of course everyone's problem might be caused by different reasons. Regardless, having observed that bootcamped windows was running fine, I switched back to MacOS, and installed Nvidia web drivers, and it has been working fine since then. This may fix some people's problem too.

Same here, I went to Linux mint and I am running with no problem

Have you had any issue with Radeon graphics in Linux Mint? Also are you running Mint 20 Cinnamon? Thanks in advance. Charlie

Well, I doubt running under MSWin is going to help it. As well as trying to install any variety of MacOS versions, I've also tried Fedora 39 & 40. The machine will lock up before it ever finishes an install. I had been running it with the panel off and using an external display (so I could have a fan blowing directly on the mainboard and GPU) and now it just keeps shutting off.

Next thing is to look at what's currently available for rPi-like SBCs, remove all the Mac system boards and make it into a large Pi-Case.

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