27 iMac (2012) crashes and requires smc reset to turn on

Mine also crashes during games more frequently. originally I only noticed it during games but recently it's crashing at random on the desktop too.

OK Guys,

so it's just shutdown again after nearly a month of no problems....aagh!

No warning (as usual) and this was after being in at an Apple Authorised Reseller recently, who could not replicate the issue.

I was editing a few pics today in the Photos app and then it switched off.

I've just got off the phone with Apple Support who are collecting it hopefully in the next 2 days to take it away for repair. They seem to think it's an hardware issue but won't say what it is until they've had it in for repair.

I'll let you know how it goes.

Just received my iMac after the third trip to the Apple Store. Because the problem doesn't show up during diagnostics or stress tests their suggestion was to wipe the drive again, but for me to do fresh installs of all of my software, the first time they wiped my drive I restored from a back up. After doing fresh installs the problem surfaced once last night, and again after a few hours of editing today. And so it goes...

I've had mine back from the store now for a day and it hasn't shut down in that time. While it was there it had a power supply replacement. Looks promising but will update you all if anything else happens.

I'm beginning to think the power supply is the root of the problem. It seems to be the only thing that some people have had replaced where the problem didn't at least immediately resurface.

They seemed pretty convinced this was the case. The engineers pointed to the log showing that there had been a power interruption when it had switched off. They replaced it with a new 300W power supply which I assume it standard?

Did you run Apple Diagnostics to determine of it is hardware related?

https://support.apple.com/en-gb/HT202731

Yes but it showed nothing was wrong that it could detect.

If you don't mind me asking what do they charge for a replacement of the power supply? I still have applecare, but after six months of this problem, and considering I basically make my living off of this iMac, it's almost just worth it for me to pay out of pocket and move on if it will actually remove the issue.

For the third time in assistance in an Apple Store.
Now it seems they are going to change the Hard Disk and the power supply for a cost of € 385,42 but I am quite sure that this won't solve the problem of the shut down.

From Italy

It cost £85 GBP including tax. Which is a lot less than a new logic board at around £500GBP so I'm hoping it's done the trick. I have 90 days warranty on the new part so I'll be putting the machine through it's paces intensively until then. I will update if it happens again.

Thank you for the update and do please keep us posted. It's quite bizarre to me that they would replace the logic board on mine, but not suspect the power supply, especially considering the evidence and the price difference. It's also strange to me that this issue seemed to crop up in about the same time frame for many of us, but at this point I'll take anything in the name of progress.

I agree it would make more sense to replace the power supply first. The reason they look at the logic board is because the SMC chip is on there which of course needs re-setting each time it unexpectedly shuts down. When I first took my computer in the engineer suspected the SMC chip and suggested that the logic board might need replacing. It was only when they were able to see the machine shutting down on their bench that they looked at the logs and then the power supply. It's probably too soon to say if it's been completely fixed but it's promising at the moment.

I will be getting mine back early next week with a new logic board fitted, so it'll be interesting to see if the problem is fixed. After reading other people's posts I guess I may be posting again in the future with this recurring problem. At least Apple are doing something about it, however I just want a fully operational iMac back!

Same problem here (27" iMac late 2012 crashing) as everyone In this thread. I took mine into the local Apple "Mac Man" store for service and was charged $79.13 for some extended diagnostics and an overnight stress test. No crashing issues could be replicated so I was sent home. Thought it might be software issue but they were unsure. This was on 12/7/15. For three weeks no issues arose while using only safari and nothing else. On 1/1/16 the problems returned. I've kept a precise log of what's occurred thus far:

1-1-16 1:45pm... iPad connected DIRECTLY to rear USB port (using Apple cord) in rear of machine to perform iTunes backup. Backup completed successfully and iPad ejected properly. A second different iPad connected. At this point the iMac immediately crashed (powered off).

1:55pm after removing the cord, iMac powered on. Upon log in, computer crashed again. Decided to wait a couple hours before attempting power on again.

3:40pm iMac powered on. This time log in successful and computer functioning with Safari. Did not attempt to connect second iPad again.

6:20pm iPhone connected for iTunes back-up and update. During update, iMac crashes & powers off.

6:55pm iMac powered on. Upon log in crashes again.

7:25pm iMac powered on. Log in successful and computer remains on. Did not attempt to connect iPhone again.

1-2-16 safari & photoshop used to edit 3-4 jpeg photos. No issues.

1-3-16 safari used no issues. Seagate portable hard drive attached directly to rear USB port to transfer several jpeg file photos. No issues.

1-3-16-

1-7-16 Safari only usage. No issues. Computer remains in sleep mode after 15 minutes & powers on next day when pressing space bar. Four days, no issues.

1-8-16 6:33pm a Delkin photo card reader is attached directly to the rear USB port. Photos (three total RAW files from a Nikon D800 camera) uploaded. Upon appearing on screen in the apple photo window the iMac crashes (Powers off).

6:58pm Delkin card reader removed. iMac powered on. Upon log in crashes again.

7:30pm iMac powered on. Log in successful. Safari used no issues for remainder of day. No attempt to attach card reader again.

Someone had had asked about service & repair charges. Here are my quotes for Wisconsin Mac Man store quoted 12/7/15:

Power Supply (part) $103.51

Logic Board (part) $799.00

Labor rate per hour $75.00

Diagnostic charge $75.00