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

It is the Delta PSU.

Exchange it with the LiteOn or start switching of the iMac during night. This solved it for me.

I also opend it up, installed an SSD and HD and I cleaned the fan and all fan holes in the chassi. Since then no single shutdown but I also switch it off during night...

have you tried an hard video rendering with imovie?

try 20 minutes of rendering and see if it will be done.

and please try also a reset of PRAM (another thing that shutdown the imac with our problem)

after swapping out the psu for a new Liteon psu, our iMac has been rock solid. It has been since mid September. Keeping our fingers crossed.

i think that there is a series of bad PSU.

who have change it could have back a good one or another bad one.

When the new is another bad one, who repair the imac think that the problem is in others imac part and begin to change parts and parts....

LOG file don't see any alert, as you unplug the power chord.

so i think that the problem is the PSU. but whe have to hope to have a good new one and not a bad new one....

Just an update. I received my iMac today with a new Logic Board and PSU and clean OS install.

After replacing my PSU and having it fail I called AppleCare and was able to get a senior support tech to allow me to bring my iMac in for repair without any cost to me.

Don't give up. Make the call to Apple care and let them know a 3-4 year old system you paid 3k+ for shouldn't be failing. Will keep you posted on how the machine runs.

I thought I would give my 2 cents worth into this thread. I can't believe it's been going on since 2014.

My issue started a little differently.

I have a late 2013, 27 inch iMac. About 2 months ago I heard a buzzing noise coming from the bottom left hand side of my iMac. I did some searching on Google and up came threads with people who had a similar issue. It's amazing once you have an issue, doing a simple search you find out you're not the only one.

After reading through various threads I worked out it was most likely a faulty power supply that needed replacing.

I took my iMac to my local Apple Store, told them about the buzzing noise and they said that had heard of this before and they will check it out and fix the problem. As it turned out, it was a faulty power supply, which they replaced.

And it totally fixed the buzzing noise...Yay.

Anyway last week, out of the blue, 2 months after the power supply being replaced, my iMac just shut down by itself. I had to reset the SMC to get it to start up again. I had to do this sometimes 3 or more times in a day.

I did some searching on Google and this thread came up. I had never even heard of this issue before this thread.

Anyway, straight away I booked in to see the genius bar last Thursday at my local Apple Store. I took my iMac in again, and told them the whole story. I even mentioned this thread and said that it looks like a fault and Apple hasn't acknowledged it yet. I even said it may be the brand of the power supply. But they weren't really interested in hearing about this thread. They also said anything is fixable....while I agree, this thread left me feeling deflated.

They said they would do a full diagnostic test on it which takes over 5 hours and see if they can replicate the issue, which means they will have have my iMac for a few days.

I wasn't feeling too positive about it after reading this thread with no one having a solid solution to this issue.

Anyway, I got a call from Apple on Sunday saying my iMac is ready to be picked up. And of course, it passed all diagnostic tests without any issues, and they couldn't replicate it shutting down by itself. They said they they even did a CPU dump which means they worked the machine very hard to get it to crash or shut down and it didn't.

I was thinking this is just typical.

He then told me just to be safe they replaced the power supply again with a new one. When I heard that I felt a bit happier, as at least they had done something even though they found no issues.

So here I am sitting typing on my iMac, I've used it for a few hours here and there and it hasn't shut down.

I'm still not 100% convinced and I am just nervously waiting for the thing to shut down based on everyone else experiences.

But what I am certain about is I think it's a power supply issue.... first I get the buzzing noise...the power supply gets replaced and the buzzing is fixed. Then I get the shutting down issue. It's too much of a coincidence.

So perhaps the initial new power supply was faulty. Now they have replaced it with another one, I'm hoping that fixes it.

Only time will tell, but I will update everyone here if it shuts down again and I need to take it back to the Apple Store.

SOLVED SOLVED SOLVED SOOOOOLVEEEEEEEED!!!!!!!!

today I changed by myself the power supply.

I bought a Liteon instead the Delta (Delta is the PSU that was installed in factory on my imac).

I followed the guide on ifixit.com

After I changed the PSU, i've run the imovie rendering that ever shutdown the imac,

and....finally..... it has completed it without shutdown!!!!

it is a very hard rendering!

CPU temperature reached 76°C but no shutdown.

I'm very happy!!!!

if you look pictures, liteon PSU is different from Delta PSU.

I hope that this is a final solution.

but if it appears in the future, i know that the problem is the PSU,

and with 65€ i can solve it again!!!!

Good for you! I've done the same and all has been all good since then. Apple needs to dump (or fix) the Delta PSU!

That's great news.

Well since I got my iMac back from the Apple Store with a second Power Supply replacement, it hasn't shut down . I asked them what brand power supply they used and they couldn't tell me.

At least I now know that if it shuts down again I bet it's a Delta brand, so I need to get a Liteon PSU as Hank K mentioned earlier.

So this isn't all doom and gloom. This whole thread had me nervous.

I have the same problem - it's been going on for 3 years but I had the power supply initially replaced when the problem first arose over a year after I bought it. I had my HD replaced too as Apple did a recall on that particular one (it died before they recalled it unhelpfully!).

It worked for around 6 months before it started again.

If you are in the EU and you can prove there is a hardware fault you are entitled to a replacement so I'm going down that route. I have to take it to a 3rd party approved repaired for them to replicate the problem (with the system wiped of software). If you're in the EU, don't go down the route of trying to mend it yourself and spending your own money. If you've paid thousands for a machine, you are entitled to a certain length of usage out of it and this thing has just been one problem after another. Worst computer I've ever owned and put me off buying new. I've always bought refurbs!

I owned many assembled pc in my life. power supply is a fragile component also in PC. i changed several psu in my past pc. also in imac is the same problem. but in the PC is very simply replace them. in new imac the PSU is more expensive and difficult to replace it. this is the real matter. but we can't consider trash the imac only for the psu. because also in pc there is the same problem. it is like consider trash a car because the breaking pads need to be replaced every 20.000 miles.

But apple have to do somethings for the Delta psu. because they are not good

As I posted earlier, my liteon power supply continues to work great after replacing the delta supply.

I see people posting that the delta supply is bad and the liteon is good. How do people know that the liteon won't fail in 3 years. My imac lasted 3 years with the delta and worked fine. Has the liteon been around for 3 years. If someone has tested these supplies against each other i would love to see the results. I would not leap to the conclusion that the liteon is better.

Wow. 32 pages of replies to this problem and I'm adding another to the pile.

Same problem on a late 2013, 27" iMac. Only starts up after being unplugged for a time. Like others have said the longer it's unplugged for the longer it seem to run. Average about 10 minutes after being unplugged for 12 hours. It then shuts itself off as if the power was lost. Sometimes I'm able to restart for a few minutes. Have started in Safe Mode, reset the SMC and NVRAM with no change. Added another Admin user and logged in with that and same result.

This computer is new to me having bought it used. Had very little use and I trust the seller. There may be a lesson here but I'm still praying for a simple solution but as time progresses I fast loosing hope. Have a Genius Bar appointment for next week. Investing a bunch of money in it won't make sense to me. Should have bought new or not at all. No AppleCare at this point.

Don't be too concerned....I'm convinced it's a Power Supply issue, that is very cheap to fix by Apple.

The only problem is I think Apple are using the Delta brand power supply which are prone to issues. so I have had 2 replaced in the last 3 months.

They put a new one in last week, and so far no shut downs. But they couldn't confirm what brand they put in for me.

Apparently the Liteon brand seems to give people no issues.

So a (hopefully) final update from me on this thread. I've posted before on here but it's been a while - I've had the same problem as everyone else.

To date my iMac has had it's HD replaced (under the fusion drive replacement program last year), two power supply replacements and finally a complete logic board and airport card replacement just last month. None of these fixed the issue and now finally to their credit Apple have offered to replace the computer. Not bad service considering it's coming up on 4 years old.

I did mention about the different brands of power supplies but unless you can speak directly to a senior engineer they're not interested.

I hope this gives some hope to anyone still suffering with this problem. Go through the Apple store process and once they've seen that the problem persists after three or more hardware changes they should feel obliged to replace the unit. It's a pain while it's happening but it has resulted in a brand new iMac for me.