2011 iMac randomly restarts

[Hirakata]

Wondering if there is anyone with more iMac internal knowledge than I or an authorized repair shop.

I have an iMac 12,2 that's been having issues. It suddenly began to randomly restart and I have no idea what the issue is. And I mean it's TOTALLY random. It can work for an hour or two and be fine, and other times it will be used for less than five minutes and restart, only to restart in five minutes or an hour later. When it restarts, there is no restart message and it goes straight to the login screen. It also does not make a report of the restart.

I've tried clean installs, installing older OS's, booting from an external HDD, run the AHT, run memtest, removed all four 8GB RAM chips and tested each in each slot, installed the OS on separate internal drives (I had previously installed an SSD and a HDD at separate times years prior) and nothing seems to work.

I took it to Apple and they said it was an issue with the drives. The the Apple tech merged the two drives into a fusion drive and said it was working fine now. I took it home and it restarted with ten minutes. I called the Apple tech and he basically said take it to an authorized repair shop, because it's too old for them to work on it at the Apple Store(?).

Anyway, I took it to a local, well known, and well thought of (even by me) authorized repair shop. It passes every test. They retried many of the things I did above and after a few weeks came to the conclusion it was the logic board. They replaced it with a new one, and and that did not work because it still randomly restarted on them. Now they have no idea what it could be. As a last ditch effort they're going to test the graphics card and I suggested testing the power supply also, which they said they would.

Anyway, anyone in MacRumors world have any ideas?

 

[nambuccaheadsau]

Power Supply can be awkward to diagnose because of its inconsistent dropouts.

Ask them to leave it on overnight. Apple Stores only handle computers built within the last five years, at least that is the way it is locally here.

 

[Hirakata]

Power Supply can be awkward to diagnose because of its inconsistent dropouts.

Yes, but I'm guessing if they use a different supply and it does not restart, then we have the answer.

Ask them to leave it on overnight. Apple Stores only handle computers built within the last five years, at least that is the way it is locally here.

They've pretty much had it on 24/7 for weeks.

 

[Fishrrman]

It's a 2011, is this correct?

In that case, I wouldn't sink too much money into it.

I'd start shopping around for a replacement...

 

[Hirakata]

It's a 2011, is this correct?

In that case, I wouldn't sink too much money into it.

I'd start shopping around for a replacement...

Yeah, I'm not planning to spend much on it. I have the new 18,3 so I'm not sweating it. But if I can get it fixed for a few hundred bucks, I will. It's still a good machine.

 

[tn-xyz]

some models from mid-2011 were plagued with the symptoms you described, because of the faulty AMD Radeon HD 6970M.

 

[padams35]

My 2011 started randomly shutting down every couple of hours/days last January. In my case the clue was that turning on the overhead lights could trigger a shutdown. I have no clue if my issue was caused by a degraded power supply that had grown less tolerant of line noice, if my surge protector was failing safe, or if something changed with the local power grid but my issue was fixed by replacing the old $9 surge protector with a sturdier/new $20 EMI/RFI filtering model.

If the restarts only occur at your place and act as if there was a brief power failure then replacing the surge protector / UPS might be worth a try.

 

[Hirakata]

some models from mid-2011 were plagued with the symptoms you described, because of the faulty AMD Radeon HD 6970M.

Yep. This one already had the card replaced early last year. Could still be another bad one. They're going t test it.
[doublepost=1510267765][/doublepost]

My 2011 started randomly shutting down every couple of hours/days last January. In my case the clue was that turning on the overhead lights could trigger a shutdown. I have no clue if my issue was caused by a degraded power supply that had grown less tolerant of line noice, if my surge protector was failing safe, or if something changed with the local power grid but my issue was fixed by replacing the old $9 surge protector with a sturdier/new $20 EMI/RFI filtering model.

If the restarts only occur at your place and act as if there was a brief power failure then replacing the surge protector / UPS might be worth a try.

I had originally thought that this could be the issue, but they can reproduce it at their shop.

 

[flyingdoctor88]

Wondering if there is anyone with more iMac internal knowledge than I or an authorized repair shop.

I have an iMac 12,2 that's been having issues. It suddenly began to randomly restart and I have no idea what the issue is. And I mean it's TOTALLY random. It can work for an hour or two and be fine, and other times it will be used for less than five minutes and restart, only to restart in five minutes or an hour later. When it restarts, there is no restart message and it goes straight to the login screen. It also does not make a report of the restart.

I've tried clean installs, installing older OS's, booting from an external HDD, run the AHT, run memtest, removed all four 8GB RAM chips and tested each in each slot, installed the OS on separate internal drives (I had previously installed an SSD and a HDD at separate times years prior) and nothing seems to work.

I took it to Apple and they said it was an issue with the drives. The the Apple tech merged the two drives into a fusion drive and said it was working fine now. I took it home and it restarted with ten minutes. I called the Apple tech and he basically said take it to an authorized repair shop, because it's too old for them to work on it at the Apple Store(?).

Anyway, I took it to a local, well known, and well thought of (even by me) authorized repair shop. It passes every test. They retried many of the things I did above and after a few weeks came to the conclusion it was the logic board. They replaced it with a new one, and and that did not work because it still randomly restarted on them. Now they have no idea what it could be. As a last ditch effort they're going to test the graphics card and I suggested testing the power supply also, which they said they would.

Anyway, anyone in MacRumors world have any ideas?

Dear all, I had the same problem. In short: Had three new graphic cards over time, also three new power supplies (internally). Sudden restarts again and again. Had SSD Fan control running to no avail (SSD in main slot). Than I linked fan control to a piece of software called "macs fan control". It allows you to set fan speeds manually. There I set CPU fan to 1200 rpm. It is normally around 600 rpm. Since then I had never ever a sudden restart again. Its like a new machine. Yes, power supplies may be faulty, as well as logic boards. But this piece of freeware made the business. So, the root cause for trouble - at least in my machine - was random overheating of CPU and its environment. And this iMac is still a mighty fine machine - look at its benchmarks as compared to benchmarks of more recent machines.