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

At my home my late 2012, 27" iMac used to shut down every day, sometimes several times. I used to unplug the computer overnight to stop this behaviour.... then I had Apple service center testing my computer... At first they found nothing wrong with my iMac! I insisted that they should continue (I was away on vacation for two weeks) At the 12th day of constant stress testing, the computer finally shut down completely. Apple service center replaced the power supply (PSU) and that is the end of the story.... I hope... Cost me about 250 Euros to fix this because my apple care plan just ended. 😟 The iMac has worked perfectly since... 70 days of very intensive use and so far so good!

My specs:

• iMac (27 inches, late 2012)
• 3,4 GHz Intel Core i7
• 8 Go 1600 MHz DDR3
• NVIDIA GeForce GTX 680MX 2048 Mo

Hi Nick,

Shutting down iMac overnight and also unplugging the power cable work for me.

Before I just shutdown iMac overnight without unplugging the power won't work.

Thanks Nick.

Hi Just It,

nice to hear.

I now use a wireless remote control to unplug to cable. Its a bit easier every night 😉

Good thing is that still there is no single shutdown since I started it. Even if it runs during the whole day.

I really think they have a problem with 24h powersupply. The smc may needs to "rest" sometime :-)

Cheers,

Nick

Well, I did it! Changed out the Delta PS for a Liteon, now we'll see if the fix works!

For one thing, the screen is much brighter. I might have to adjust

Since the new Liteon PSU was installed, the baby has been perfect. I'm convinced that the problem is in the or Delta PSU.

Apple needs to be honest and recall these Macs.

Hank

Apple needs to be honest and recall these Macs.

I expected better of Apple than this.

They appear to be hoping that the affected users like us will just give up.

i took my imac 27 late 2012 apart and changed the thermal paste. I had read someone say that was the reason for the heat problems and would fix the reset problems. I had installed macs fan control and could see the temp spiking just before the resets. Alas no luck.

When i put the computer back together i attached the monitor screen with masking tape instead of double stick tape in case the paste didn't work. Then i saw this thread and decided to try the new power supply. Amazon sells the power supply (Liteon) for $65.97 with shipping. So i ordered it and got it today. Just installed and stress tested it. I test with high def video files at full screen. These seem to spike the gpu temps on macs fan control. Anyway it seems to be working. If i see another shutdown i'll report back.

My computer is now failing during shut down.

When I next try to start the computer up nothing happens. I have to unplug it, wait a while, plug it back in and then start the computer up.

It might be time to replace the Delta PSU with the Liteon.

Mine's been fine since I did that!

Had this problem for almost a year with random shutdowns as much as twice a day. 1st trip to Apple store came back with the usual 'we couldn't find anything wrong with it'. Just had a 2nd trip to the Apple store and told them that I believed it was the PSU at fault and they replaced it. Computer was ready 24hrs later. This was almost 3 weeks ago and haven't had a single shut down since. I'm keeping my fingers crossed.

Also, Apple didn't charge.

Reporting back:

zdz80 wrote:

i took my imac 27 late 2012 apart and changed the thermal paste. I had read someone say that was the reason for the heat problems and would fix the reset problems. I had installed macs fan control and could see the temp spiking just before the resets. Alas no luck.

When i put the computer back together i attached the monitor screen with masking tape instead of double stick tape in case the paste didn't work. Then i saw this thread and decided to try the new power supply. Amazon sells the power supply (Liteon) for $65.97 with shipping. So i ordered it and got it today. Just installed and stress tested it. I test with high def video files at full screen. These seem to spike the gpu temps on macs fan control. Anyway it seems to be working. If i see another shutdown i'll report back.

Its been 10 days since replacing the power supply. Everything works and no shutdowns. The old supply was a Delta.

I have looked at the old supply for problems(puffed caps) and didn't see any. I have since looked harder and one of the 1500 uF 16volt caps looks different. It has very faint signs of puffing.

I have no idea how long the new supply will last and am actually thinking of buying a spare.

Surprise, surprise.

iMac 27" 2012 3.4 I7 1 Gb Fusion 24 Gb Ram running El Capitan

Last week it just turned off. Thought it was electricity interruption. Nope.

Had to turn off at the wall to restart.

Has been randomly turning off all week. Can get it to run for a few days and then it all starts up again. Today has been the worst. Lucky to get 20 minutes out of it before a shutdown. So far 6 times today and it requires a few minutes with the power off at the wall before it will boot.

Initially tried UPS but no go, looked at fan speeds and temperatures. Nothing extreme. Tends to crash around 54 degrees Celsius on the GPU. Have tried with boot disk running Yosemite and Bootcamp Windows. All shut down so not software related.

I have located many posts on forums explaining the same issues. Console indicates "0" as the cause which follows the trend.

Am going to approach Apple for a response before I endeavour to replace the power supply.

After reading through the whole 31 depressing pages of this thread i thought i'd add my name to the list.

I have the same exact problem as the rest of you, the imac cuts off, need unplugging for a while before it will work, then does it again etc.

Mine is the 3.2 i5 processor and have 24gb RAM

I use mine mainly in windows via a boot camp partition so it's happened mainly there although it has done it in OSX too.

I've used windows 7 and 10 and the last couple of varieties of OSX while this has been happening.

(I've also never had Safari installed in Windows and never use it in Mac OS in case anyone actualy believed that could be the cause)

I haven't contacted Apple about the issue yet, as with the unplugging workaround and the hassle of dragging a 27" computer through a shopping centre i've just been putting it off.

My first thought when it started happening was the PSU and that still seems to be the most likely cause.

This is my first mac computer and will most likely be my last.

Same issue here as well. I took the machine to a certified tech, they couldn't replicate the issue. Once I had the machine home and running it started right back up. Brought it back in and they were able to replicate the problem. They replaced the PSU and I went home happy as a clam. Within three weeks the problem was back and that's when I started digging for more info and wound up here.

I've been on a mac for nearly 15 years and for the first time feel truly let down. Unfortunately I'm not going to move my workflow to a PC and am faced with swallowing another 3k + for a new home machine.

So, is it too soon to determine if the Liteon power supply may be a answer to the problem ?. Have ordered one and decided there is nothing to lose in having it fitted.