Why is my imac shutting down by itself?

Try changing the power outlet (best to just insert to wall socket). I have the exact same issue with my late 2012 iMac shuts itself off randomly And unable to power back on unless I unplug my powercord for 10-15mins before plugging back in. I bought it to Apple Store to run some test but no issue was found. Then I thought perhaps it might be the power issue. I then went and invest a new power extension and bought it back home and ran it again. When home, start my machine, ran "gw2", enter WvW, hop in the roaming train with atleast 50+players(this is to stress test my machine to see if any shutting down occurs), ran it for 5+hrs, and since then no issue arises. It ran extremely smooth So please give it a shot before investing a bunch and replcing any hardware.

Robert,

In my case, the power was really, really OFF. No fans, no lights, no activity, no reawakening. It was DEAD. Replacing the power supply put the machine back into operation without failures for a period of at least 18 months the first time and 28 months the second time.

HOWEVER: The third iteration only lasted two months before it again started powering off again. I'm going nuts. I am really reluctant to buy a new machine if the problem is going to continue. Does anyone know the most recent machines that are shutting down?

The first time it happened, Apple swapped out the mother board, and I restored the original memory before replacing the power supply.

Replacing the power supply seems to help for a while. I associate the power down with high graphics use: Civ V, Steam, InDesign, Photoshop, other activities that draw on the video card. maybe something there.

I agree, Apple knows -- or SHOULD know -- more than they are admitting. I suspect there are some bad basic components in use somewhere, like the bad capacitors that were made and used by the millions about 15 years ago. From Wikipedia:

"The capacitor plague was a problem related to a higher-than-expected failure rate of aluminum electrolytic capacitors with liquid electrolyte between 1999 and 2007, especially brands from some Taiwanese manufacturers.^[1][2] The capacitors failed prematurely due to an incorrectly formulated electrolyte which caused corrosion accompanied by gas generation, causing the capacitor's case to bulge, venting the electrolyte and sometimes rupturing the case.

High failure rates occurred in many well-known brands of electronic equipment. The problem was particularly evident in the motherboards, video cards, and power supplies of personal computers, causing failures of these devices." (emphasis mine).

The story behind those is a tale of corporate industrial espionage and counter-espionage that cost thousands of bystanders a lot of money.

So, you are right, i don't know the precise cause of the failure; Replacing the power supply resolved my problem for a period of time for the repair cost vs. a new computer. But it didn't solve the problem. And I'm ****** if I'm going to give Apple another $2,000 for a machine that craps out in the middle of my work.

Jay

I'd like to note another thing. I have to reset my SMC in order to get the computer to restart. It will not restart unless I pull the plug for a while, thus resetting the SMC. I haven't figured minimum time. What is it about the SMC that is involved in these shutdowns?

According to Apple, my latest and greatest EFI firmware is supposed to be

which is exactly what I have showing in Hardware About my machine info. They do not list a current SMC firmware for it.

When I download the IM firmware and attempt to install it, it says "this software is not supported on your system". NOT 'this software is already installed on your system' which indicates a incompatibility with Yosemite, what I'm running now. I get the same message trying to install older or newer versions of any of Apples firmware updates. Has anyone had luck dialing back on OS levels? Can anyone explain why this is so?

This suggests that the SMC firmware or even the hard wiring on the Intel chip may be defective - leading to all the different kinds of onsets reported here. Apple says the SMC is involved in sudden power downs, and I know my machine has to have it reset to start again.

I also note that my machine stays on longer at my office and that it can take more programs open and a heavier graphic load, but it does pop off with InDesign, Photoshop, Illustrator, and Civ V running off Steam all working. That's with 8 gig of memory.

Jay,

I'm at my wits end regarding random shutdowns with my iMac (late 2012) i7. I have tried everything, except a clean install of OS 10.10.2 - coming soon.

Payed a lot for this machine, babied it all along, and yet it fails. Unexceptable!

This will fix it.

http://apple.stackexchange.com/questions/76978/how-to-stop-mountain-lion-to-stop -shutting-down-and-closing-all-my-applic…

Did you check your prefaces to see if you have a sleep option on (goes to sleep after a preset time)

So, did anyone ever find the absolute solution to this problem?

Right now my iMac is at tech support for the third time, and i'm getting ready for them to tell me they can't find anything wrong with it. So please if someone found the solution and has been using the imac for months without any more problems please share. The most common solution I've read here has been related to the power supply...I think.

I'm sure there are more that just one cause for this problem. Mine was solved by replacing the power supply. That was Apples repair advice and solved it - 2 months up and running again.

I have had unexpected shut downs for 3 months. Since December (when the computer was 2 years old aprox.).

As I stated above, after visiting 2 different Genius Bars where they could not fix it, this is what I have accomplished in order to keep using the machine with no shut downs.

I usually had multiple shut downs on a regular day. Sometimes after 2h, sometimes after 7h. When that happened, I needed to unplug the iMac for 15 minutes (I ended up calculating with iOS Timer).

So I though maybe there is a component being charged unexpectedly until the mother board shuts down itself for security. That would explain why changing the Power Supply doesn't work.

Anyway, I decided to connect the iMac to a multiple power socket with a switch. When I'm done working with the iMac, I shut it down and I also switch off the power socket.

Doing that seems to "uncharge" whatever was going on in the iMac as when I come back to turn on both socket and iMac I can work with it for more than 24h.

I've had no shut downs for 3 weeks now. And after having 3-4 shuts downs every day., this is something.

So, I took it back to the tech support to run more tests (3 more days) and luckily the iMac shut down in front of their eyes so they managed to get the apple warranty. They are waiting for apple to send the replacements (I live in Ecuador) and hopefully the problem will be solved. My only concern is that apparently apple is only sending the logic board for replacement, and i don't know if this will be enough to solve the problem.

I'll keep you updated in case someone still needs answers on this matter.

They just replaced the logic board, power supply and a cable on mine

seems to be running correctly now

I bought the 27" IMAC in 2013. It started to shut off by itself, but never before it had been on for at least 4 hours. Then the ON button would not work unless I unplugged the power cord, waited a minute or so, then replugged it. Then it would reboot OK after pushing the ON button.

Many days it would never shut off. It seemed to shut off more often when my room was warm (upper 70s, 80) during the summer. I called Apple support and she suggested to basically do a fresh install of the OS, etc. I did not want to do that since I felt the problem was heat related.

Then for months my iMac did not shut off. But the other day it started doing it again. Then I unplugged the power, replugged, then it rebooted OK.

But I just "may" have figured out my problem. I hope it helps others here.

Ever since I bought my IMAC I have never heard the fan operate and the entire back of the metal monitor, near the vent and also even the metal stand were very warm to the touch. Way too warm IMHO. After searching Google for "IMAC fan does not work", I came across this free software app:

http://www.macupdate.com/app/mac/47386/macs-fan-control

It will show your fan speed and also sensor temperatures (Ambient, CPU, GPU, LCD, Mem Controller etc. It works with Yosemite.

So I downloaded this neat desktop app and it showed my fan set on "AUTO" control but the current RPM was ONLY 1200, with the minimum RPM listed as 1200 and maximum as 2640.

The Ambient temp was 8 C (46 F), and the CPU, GPU etc. were at 44 or 45 C (~113 F). So I used the Macs Fan Control interface to set the fan at a constant value of 1920 RPM (right in the middle of the 1200 - 2640 RPM range).

Immediately I could hear a very quiet "whirringgggg" sound of a fan (which I had NEVER heard since buying the iMAC) and can actually feel air coming from the back vent. After an hour or so, the entire back of the IMAC that used to be very warm, now feels "normal" and cool to the touch, not overheated like before.

Now, just an hour after increasing the fan speed from the minimum of 1200 RPM to 1920 RPM, the CPU, GPU, etc. sensor temps are now showing as 37 or 38 C (~98 F). 15 degrees F cooler than before when the fan was only running at 1200 RPM.

I really think this solved the problem of my IMAC shutting off by itself. Maybe there is a problem with the "Ambient sensor" since it is 68 F in the room, NOT 8 C / 46 F. This may have kept the fan running at only 1200 RPM (minimum) while set to the "AUTO" setting.

Hello again,

Bringing updates on my case. So, since the iMac shut down while they were running the apple tests at the tech support place, they were able to make the warranty work. After two more days apple sent the logic board for replacement. Its been a week since they changed it and everything seems to be alright now, I haven't had any problems so far.

I hope you are all solving your problems as well, cuz this issue is in fact very annoying and stressing.

Hi Jay, that is not much RAM. Are you watching Activity Monitor to see what is happening? Cheers Bryce

…Does this help or assist? http://9to5mac.com/2013/08/16/apple-opens-graphics-card-replacement-program-for- some-mid-2011-imacs/