Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor

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iMac keeps randomly restarting

My iMac keeps restarting every time I turn it on. Sometimes it doesn't get to the desktop before restarting and other times it restarts while using it.

I have already replaced the power supply with the same result. I also have tried unplugging both the HDD and the SSD and it still was restarting. I have tried switching out the RAM from another iMac and it still restarts.

When it restarts, it randomly shuts off and then boots again, sometimes over and over.

I have already taken it to an authorized Apple tech, and they told me they could never get it to reboot... the closet Apple Store is over 3 hours away so I am trying to troubleshoot this myself.

Any ideas on what I can try next? Thanks for your help!

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I think you started down the right path as being a power issue. Given the fact the Apple tech couldn't get it to fail when he had it I suspect your issue is within your homes power not your system.

First you'll need to get a cheap AC Outlet Tester to check your outlet to see if the the outlet is correctly wired. You could also have a grounding issue if you don't have a three prong outlet. This is were you will need to call in your local electrician to fix the outlet. Even still you do need to make sure the outlets wiring is correct (don't cheat here, you need all three wires). Following the wiring back to your fuse/breaker panel make sure you have a 20Amp circuit for 120volts and ideally you should have a dedicated line for your computer and your peripheral gear. Make sure the buildings Ground circuit is in good shape. Often a grounding rod stuck into the ground or strapped to the metal water line feeding the building. Over time the wire and/or the connection point corrode (green stuff) and need to be cleaned. The rod can also have degraded and may need to be replaced or positioned in a better location to be effective. Many people put electricians grease on the exposed surfaces of the connections after wiring it up to help prevent corrosion.

So we went as far as the fuse/breaker panel and we still have problems. You may need to get a UPS to stabilize the power as your power provider maybe having problems giving you reliable power. Many of the better units have power meters which can show you how good/bad your power is.

You could ask your utility provider to test your power:

Have them put a power monitor in your house for a good week or so. They may need to service your homes power feed or replace a transformer that feeds your neighborhood.

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Thanks for the help. I originally thought the same thing, that something was wrong with the outlet. I plugged the iMac into my UPS and it still has the same problems. My other iMac is plugged into the same UPS and it doesn't reboot randomly. I tried plugging it into a different outlet not on the UPS and it was still rebooting. I'll pick up an AC outlet tester though and see if the outlets are bad.

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You could try swapping the AC power cords between your systems to see if the cord is bad (less likely though)

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Okay, I have tested the outlet and all seems well on that end. I also tried using the power cord from the other imac and it still restarts randomly. Any other ideas I can try? I might try and take it to the Apple Store next time I'm in Chicago at the end of November, but I really don't want to spend more than $300 trying to get it fixed. I'm worried it could be the logic board which I've read costs ~$600 to replace.

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What happens when you take the system to work (or someone else home that is not too near you) and use the power outlet there? does it react the same way?

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Took the iMac to work and it still had the same problems. Work is about 30 miles away so on a totally different power grid. Also checked the outlets home and everything seemed fine.

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When the iMac starts-up, the graphics card supposedly uses the Intel processor does the initial work. Once you arrive at the stage when you see your user accounts, the graphics processing has been delegated to the on-board dedicated graphics card at this point.

This is also why the you can use older iMacs pre-2014in target display mode by hitting the F-2 key.

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I have the same problem with a refurbed model I bought from BestBuy.ca with 4 years of Bestbuy warranty... The computer clicks and shuts off as if the cord got unplugged, then reboots. Sometimes happens during the boot process, other times during regular usage (though seems to be frequently triggered by GPU usage... but not consistent).

Same results with Lion, Mavericks and Yosemite. Pretty sure it's hardware.

BestBuy Geeksquad replaced the logic board, and it still crashes. I, like you, have tried different cord, different outlet, with and without UPS, all with the same random results. Other 2008 iMac in same UPS is solid. I have to assume it's the power supply.

Going back to best buy tomorrow for them to send away again. Their no-lemon policy states that if they replace hardware 3 times, they'll give me a whole new equivalent or new current model as a replacement. I'm looking forward to my brand new 27" iMac soon!!

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Having same problems but it's really weird since sometimes it starts like if it was new and sometimes it keeps restarting when I turn it on.... But then after several times it restarts by itself I can use it like normal... Second day with this problem and let's until when my mood can take it... Closer Apple support is about 2 hours from here.....

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My iMac 27 Intel Core i7 OS X Yosemite 10.10.3 Prosessor 3.4 with 2 HD discs keeps restarting everytime I turn it on. Sometimes it doesn't get to the desktop before restarting, other times it restarts while I use it.

When it restarts, it randomly shuts off and then boots again, sometimes over and over. But it doesn't restart when using disk utility program. It just began after test & video card replacement at Apple store service ("Gatortech" in Gainsville, Fl.) The guy replaced video card and asked me to replace power inverter. I didn't get it why and what for, until I got home and turn on iMac. Have tried everything: diagnostic hardware, reinstall OS to the initial, uncheck "Automatic restart..." , recovery both HDs, Mount & Unmount HD, even reformat drives making partitions - the problem exist. Any meaningful advice would be appreciated. Thanks

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My 27" iMac. Model No. 814LL/A is crashing as well.

My iMac keeps crashing and restarting, gets grey screen with pink stripes.

Crash Report

My issues started occurring after some recent Apple updates to El Capitan, about two weeks ago.

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Crashes are mostly caused by software issues like misbehaving apps or drivers. I rare cases hardware could be the cause as well. Like a bad RAM module. Here's a good Apple T/N that goes into crashes: OS X: About kernel panics. Most of the time I try running the system in Safe Mode to see if it continues to crash. Here's a good Apple T/N on it: Use safe mode to isolate issues with your Mac.

While Apple did have a recall on some models that had a bad graphics card you should have seen some odd color or patterns on the screen when doing a clean boot (cold restart). Sadly Apple recall has ended so you'll need to get a new graphics card here.

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I'm having the same problem:

Crash Report

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Crashes are mostly caused by software issues like misbehaving apps or drivers. I rare cases hardware could be the cause as well. Like a bad RAM module. Here's a good Apple T/N that goes into crashes: OS X: About kernel panics. Most of the time I try running the system in Safe Mode to see if it continues to crash. Here's a good Apple T/N on it: Use safe mode to isolate issues with your Mac.

While Apple did have a recall on some models that had a bad graphics card you should have seen some odd color or patterns on the screen when doing a clean boot (cold restart). Sadly Apple recall has ended so you'll need to get a new graphics card here.

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Yes that is correct, when using my mid-2011 iMac in "Target Display Mode", it will freeze up, and then the iMac will eventually reboot after a minute, or two, an hour, a few hours, no set pattern. This occurs even when just using the older mid-2011 iMac in "Target Display" mode.

* The purple bars started appearing during the boot up a few months back in October 2016.

* Ran the full Apple hardware tests on the memory.

* The Apple Store ran their hardware tests, all checked out as well.

* The iMac has been completely reloaded with Mac OS, two times with a fresh install of Mac OS.

The full history of the mid-2011 iMac:

Previously, owned by a Mr. Richard Freely, the logic board and power cord had been replaced a few years ago, before I purchased the mid-2011 iMac from PowerMax located in Portland, Oregon as a previously owned iMac at a decent discount. I guess that was a mistake, should Judy purchased a new iMac, with full factory warranty.

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I have the same problem. The repair guy said that it could be the problem of logic board, so I changed a new one, but not the graphic card. When I took it home, it went well for couple of days. But then, the same problem reappeared. And I changed different electric outlet and different cord, not working. I am wondering will change the graphic card work? It's so frustrating.

Update (02/27/2017)

I think I got the problem solved.

Originally, I got the same restarting problem. So I sent it for repair, and the shop told me that it was the logic board problem. I thought since I have to change the logic board, I should upgrade it at the same time. So I changed the logic board, CPU, and SSD hard drive, but not graphic card. When it came back, it worked fine for a couple of days, but the same problem came back. Then I sent it back for test, and the shop told me it might be the hard drive problem, so they changed it and sent it back. Unfortunately, the same problem came back in a couple of days. I was desperate, and ready to buy a new iMac. Luckily, I found this post:

https://discussions.apple.com/thread/617...

In the end, I asked the shop changing the PSU unit. It's been a week, I never shut down the computer, and it never got one instant of that restarting problem.

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Same issue, response from authorized Apple tech:

"Machine worked fine for a couple of days then on restart, it showed the fault as described. Found that if the unit is cool, it will power on and boot. If it is then restarted, the fault shows. Swapped in a test power suppply. The fault remains. Issue likely to be the logic board and could be graphics card."

iMac now sold for parts and purchased new one.

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I ended up purchasing a new iMac to resolve my issue. However, the general consensus is that the technical issue is caused by the graphics card on this iMac model. A clue, is the observation of odd happenings, a gray screen with pink stripes on the screen during boot up of the problem 27 inch iMac.

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The problems have been documented over the past couple of years on Apple’s own Support Forums. Additionally, the iMacs must fall in the following serial number configurations:

The last four characters of the serial number must contain one of the following groups (for example, xxxxxxxxDHJQ):

DHJQ, DHJW, DL8Q, DNGH, DNJ9, or DMW8

DPM1, DPM2, DPNV, DNY0, DRVP, DY6F, F610

If the iMac falls within one of the above the serial number categories and is confirmed to have the graphics card issues, Apple will replace the AMD card free of charge up to three years from the computer’s purchase date. Additionally, if an affected iMac user had their graphics card already replaced at cost, the customer is said to be eligible for a refund.

https://9to5mac.com/2013/08/16/apple-ope...

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I have the same model and had this problem and narrowed it down to the video card.

Argued with the apple service guy and after replacing power inverter, problem remained. Finally failed the apple video card test and got a replacement free from Apple.

A year and a half later, and the problem has returned. Out of 1 year warranty of course. Sometimes I can run 3D benchmarks for hours with no problems, other days just reboots after starting login.

Removed the card and stable as anything. At this point a AmD 6970 is too expensive and how long will it last?

I'm going to put a slower 6770 in it this time. Sucks for high end games, but at least I can get a few more years out of what is otherwise a great system.

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