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

Ah OK good to know. I will try changing the power supply then...

It started with Safari Problems. Whenever I surfed the web with Safari, I got these shutdowns.

Then I switched to firefox which solved it for some weeks but now its coming back.

I got this solved again (don't now for how long) witch setting the fan to max rpm. Its louder, of course but since then not a single shutdown anymore. That brings me back to temp. problems which are maybe the cause. I will let you know when the shutdowns return. So far so good.

Nick,

Don't think temp is the cause, most likely your power supply unit is not powering yourAirport ( WIFI ) Card properly. I also noticed during my diagnostic testing that my Airport Card failed wake and sleep tests, those wake and sleep tests are a good indication something is wrong with power.

When I replaced my power supply unit my iMac passed tests on the Airport Card.

If temp was the main cause, then the shutdowns would be predictable. These iMacs have plent of sensors, on reaching a specific temp then your iMac would always shutdown, that's not the case here. The shutdown cause error 0 ( sudden loss of power ) logged also points to the PSU.

Glasguy,

understood.

But as I read so far in this thread there are some people who changed their PSU and after some time the shutdowns happened again. You mean this problem comes back from time to time or is there a bad amount of iMac models with the "wrong" or not working PSU? As I read, this also affects 5k iMacs, so this is a problem of more then one model?

I agree with you, if temp would be the main cause you could force shutdowns only by high temp. Thats def. not the cause. But it may affect the problem here - lower temp may let the PSU work in more stable parameters.

I just down know honestly what to do, I just can try things out and when it works, we all can be happy. Its so nerve wracking with that shutdowns...

Nick,

I seems that 27" iMac 2012 up to Retina have reported problems with intermittent shutdown. The 27" iMac service manual is the same for 2012 /2013/ late retina 2014. I'm wondering if Apple use's more than one manufacturer to supply PSU's for these iMacs, also wondering if they use refurbished PSU's for replacements. My faulty PSU is made by delta Electronics, my replacement is made by LiteOn. That makes sense what you mention that low temps may let the PSU work in more stable parameter. It a spoiler having uncertainty and no confidence when using the machine.

Thanks for that info - then it makes sense that all iMacs beginning from 2012 having these problems.

Just 10mins ago I exchanged my 1TB Harddrive with a 1TB SSD. With this I saw A LOT of dust in the iMac as it was mentioned above by other users. I tried to clean it up as good as I can. It really were flakes of dust and compressed dust. The fan was free, not jammed or something but of course also full of dust. Hopefully its now getting better. I also set fan speed back to default. The OS is controlling it now, we will see if strange behavior will occur. I'll drop a line if so.

Nick,

Can you confirm what brand your power supply is, does it look healthy when the dust is removed. Do you have white ingress marks on the PSU.

Glasguy,

sorry but I just put in a new hard dive, I did not dismount the logic board the install it. Therefore I did not see any labeling of the PSU.

I did it.

But shutdowns persists

I simply cannot imagine that Apple does not know what the core of the problems is. They are so much in control of their products and the assembly of them, our problems must be known.

I would not mind spending money on fixing my Mac, but I don't want to end up replacing part after part - and wasting lots of money - until the Mac is fixed.

Apply should be able to point out that if you have PSU model xxx or CPU model yyy etc, then you should do zzz.

Please, our son was just doing his homework on the Mac today and suddenly the Mac turned off. And since he did not know that he had to unplug the power for 1 Minute, he never got the computer turned on again.

And he was furious that some parts of his assignment was lost, which I understand.

Well, I presume everybody has seen this notice. iMac (27-inch): AMD Radeon 6970M Video Card Replacement Program - Apple Support. Clearly Apple recognize the problem with our build, models but only those fitted with the AMD Radeon HD 6970M video cards . All of our models are based on the NVidia Card. When will Apple address this ?.

Sadly does not apply. Suffering with a NVIDIA GeForce GTX 660M.

OK, so I have had my late 2012 27 inch Imac back from apple for exactly one week now after taking it back to them a second time with random shutdowns. The first time was July 14th and they replaced the hard drive which did not solve the problem. The second time, they kept if for a week and ran every diagnostic test they could. Of course, the computer never shut down. They did not replace anything BUT, they did give me a brand new power cord. I plugged it in last Saturday after I got home and I did not not shut it down until last night. Now, I am not saying that the power cord solved the problem; I am not saying maybe the computer kind of fixed itself with all the test Apple did on it; all I am saying is that for one entire week, my computer has not shutdown, and it has been acting and running like I just bought it. It is so fast and snappy, and it acts like it is supposed to. When I turned it on this morning, it powered up in seconds and I have had no issues waking it up, no shutdowns, and no sudden loss of power kernel. I am afraid to say anymore because as we all know, this shutdown thingy can occur at any time. However, so far, fingers crossed, the new power cord SEEMS to have solved the issue. I will definitely be back to report if the shut downs return. I just wanted to maybe help someone else that is having the same issue, maybe a new power cord might be the answer.

The iMac has a standard power connector so a normal power cable should fit. Have some laying around here so it is worth a try.

Unfortunately this did not do the trick for me :-(