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

After 18 months of shutdown agony I was very frustrated. The local Apple Shop could never replicate the problem or find anything wrong with the computer.

In the middle of autumn here in southern Australia the problem became so bad that the computer was shutting down several times a day, including when it was asleep with no programs running or connection to the internet or to the Time Machine backup. It also used to sometimes die when I was shutting the machine down.

The straw that broke the camel's back was when it did that during a restart after a system update and corrupted the operating system so badly that Apple Support suggested I wipe the hard drive and reinstall the operating system from scratch. Even getting the existing information off the computer and onto a portable hard drive became a nightmare because the computer would abruptly shut down while I was doing it.

In desperation I decided to do what others have done and get the local Apple Shop to replace the power supply unit. Before replacing the power supply the local Apple Shop tested the computer again and still couldn't find anything wrong. One month later and I haven't had a shutdown.

If you are having this shutdown problem I would highly recommend that you try replacing the power supply first before spending money on replacing video cards, screens, CPUs etc.

You will probably have to insist that they do that first because they will still argue until the cows come home that it is likely to be one of the other components and not the power supply. Given how often replacing the power supply has solved people's shutdown problems that is not always true.

In my case, I installed some fan controller software (called Macs Fan Control) and pinned it to the GPU PECI (whatever that is), so that the fan really cranks when it heats up above 45C. This has greatly reduced, but has not completely eliminated, the random shutdowns (which I still believe are power-supply related but may well have an overheating aspect as well). Eventually I will replace the power supply. This is my newest of about 15 macs at home and work, and it is the most problematic.

Bill, I had Istat Pro installed and looked for heat and voltage spikes before the abrupt shutdowns and never found any.

I even tried cranking up the fan speed to the maximum and the computer still abruptly shut down even though the room temperature was in the range of 5°C - 25°C and none of the temperature sensors were high.

I'm guessing here, but I think there is some sort of very transient temp spike that evades the sampling window of those programs but tells the defective power supply to shut itself off. This could be a total red herring, but it is all I got.

What would cause a heat spike when the computer is asleep and it is not connected to anything so there are no processes running?

Why has replacing the power supply solved the problem for so many people?

Why has the problem started for so many people between the two and three year mark after purchase?

From what little I understand, replacing the power supply with a LiteOn power supply has solved the problem, but not for the others. (No one answered my question above, so I am still not certain about this, but it is the impression I got in the first 36 pages of this thread.)

I think the most likely explanation is that the power supply Apple uses is inherently defective. As for your other questions, it is possible later versions of OS X unmasked the issue, or maybe it is a capacitor that starts to die or something like that. I don't know enough to offer anything other than guesses.

When you spend the amount of money I did on a computer you expect it to be usable for longer than two and a half years.

I could not accept that the way to solve the problem was to spend lots of money on randomly replacing components in the hope that would fix the problem. Others have done that unsuccessfully and spent more money than what their computers are worth.

Apple don't seem to care that their continuing denial about this abrupt shutdown problem is a PR disaster.

We are all in the same boat here. That is the reason I don't want to bring mine to Apple for repair. But I have had two well-regarded Apple-certified third-party repair places say they don't want to touch this can of worms.

The fan control at least seems to have applied a bandaid.

After reading the posts here and elsewhere I came to the conclusion that this recurrent shutdown issue is caused by a defective power supply.

I ordered a LiteOn power supply from the UK and had it shipped to Australia.

I had also broken the main body hinge so got one of these as well.

My OWC temperature sensor/hard drive cable was faulty too, so I got a replacement for that as well.

Yesterday I stripped down the iMac to an empty chassis, replaced the broken hinge, power supply and HDD cable.

I spent over 4 hours on the job, proceeding slowly and carefully using the guide from iFixit.

If you proceed carefully it is not all that difficult. You just need to get the adhesive strips from iFixit and some Loktite if you are doing the hinge.

Stripping off the adhesive with turps from the LCD and iMac body probably takes the most time. You also need to be very carefull removing and replacing the various cables.

So far everything is working perfectly. (Touches wood!).

Another update from me. It should have been close to a year that I got my power suppy replaced by Apple (so not a Lite-on one apparently) and it has not shut down once on me requiring a SMC reset. It is definitely power supply for me. It may be hard to persuade Apple guys to replace the power suppy and they insist on keeping the old one or give you that faulty one back for a fee. Funny I know.

I sport a 27'' i7 iMac with 680MX

@oomoot :

Thanks for that update. That is really good to know. I think I will just have to bite the bullet and take it to the moron bar and get it fixed. This is just driving me absolutely nuts. I have several iMacs that are older, both at home and at work, including two from 2007, all of which have been flawless. They really blew it with this one.

I mean the fix is relatively cheap for an official repair from Apple so I'd do it. But even better is getting it fixed elsewhere with a Lite-On PSU. I'm in Turkey so I just didn't want to wait for a PSU. I also was not sure if it was PSU so I thought getting it to the Apple Store for diagnostics first is a good idea (in which they of course failed to find anything wrong like almost everyone else in here). I almost had to beg over the phone for them to swap it for a new PSU (make no mistake, I paid for it, but still...)

The upside is I just had to haul the iMac once to the Apple Store. It really is a pain to carry it.

Another thing is I use my iMac seldomly. Some other people reported that the shutdowns are coming back after around six months with the original PSU replacement. As I've inquired newer iMacs were also using the same PSU so maybe they fixed something with them maybe more quality capacitors I don't know. My replacement is probably the one that they also use for the retina iMacs.

Shortly, get your PSU changed and you'll most like be fine.

So this started happening to me about 3 weeks ago on my iMac late 2013. Computer randomly shutting off no matter what I am doing (internet, video games, anything), and at completely random intervals.

Took it to Apple and they told me I needed to replace the power supply, so I reluctantly did that. Got it back a week later, and all was fine for about a week of it being on, and then 3 days ago it shut off again. Then again the next day. Then twice today.

I got a refund for the power supply they replaced, but they said the next step was the logic board. I am most definitely not paying for that since I see here that it didn't work for a lot of people. I really don't want the computer to stop working again in a few months after spending $700 to fix it.

Seriously peeved since I've had this $2100 computer for 2 years and it's already broken. I didn't get Apple Care + which I am seriously regretting now.

Hi, these days I'm having the same problem.

My iMac (late 2012 i7, 32gb ram, fusion drive 1TB) shuts down randomly with no apparent reason.

I looked some threads on the apple support community with no help.

The computer shuts down in idle and in full load situations.

Even when I'm using windows 8 with a boot camp partition.

I called the Apple support and they told me to do a full hardware test ( hold D on startup ).

It took a while (about 3 hours) but it was clean.

The guy who I talked with told me to do a clan install of the system in case the hardware test was clean. Maybe it is a software problem ( oh yes he checked the caches and .plist file too)

If it persists after a clean install I should take by mac to assistance to be checked and repaired if needed.

I'll contact the support again on Monday GTM+1 time because I had a shut down even using windows...

I guess (unfortunately) it's some hardware problem....

Hi, same problem.

My 27 iMac i5 2012 shuts down randomly, for restart unplug power line for 30 seconds, (reset SMC).

After hardware test (ok) reset imac with clean install but never same problem.

how your have resolved.

think apple support say.

THANKS