Chosen Solution
I bought a 2011 iMac used knowing that there was a problem with it “shutting off at random times” and I thought I could simply replace the power supply. After receiving the computer I noticed that the only thing that’s shutting off was the backlight because I could shine a flashlight at the screen and the computer was working fine. I then replaced the led backlight control board, but the problem persists. Now all i can think to do is replace the lcd itself, but I can’t figure out what part would be compatible. Would a screen listed from a 2009 or 2010 iMac of the same size also work? In addition I don’t know if there is a better place to buy the parts than eBay. Thanks for any help you can give:)
Update: nothing I tried fixed the problem, and then the graphics card went out completely. After putting it in storage for months I finally decided to try a new graphics card (or rather a used one from eBay, but new to me) and it worked… perfectly… and four months later still haven’t had any issues. For many this may have other causes but in my case it appears to have been a faulty graphics card. By now I have a closet full of iMac parts I tried to fix it with, but at least it works now. Hope this helps, and good luck :)
I’ve resolved my issue by replacing the LED BackLight board (cost me about 45 EUR via AliExpress). Got it fixed within hour by following iFixIt tutorial. Was quite easy to do, just take your time. If i need to do it again i could do it within 15 minutes… :-) Display hasn’t failed once since i replaced it!
See if Apple will replace the board, do not mention that you changed the back light board. I know the LEDs do not show this but experience says this is the problem: https://support.apple.com/en-us/HT203787 Due to high demand Apple has extended this period of time in a lot of cases, mention the term, “Warranty Exception”. 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. http://9to5mac.com/2013/08/16/apple-open…
I bought an used iMac with this problem for a good price to solve the problem, just like you. I got it temporary worked around, maybe you can try it. Unplugging the power for a while and putting display brightness to lowest seem to have worked around the problem for a while. I think the built in power adapter or backlight board is the issue. These are both always powered when plugged in. This week this workaround didn’t work anymore and I’ll replace both. I’ll let you know what the culprit was. If you have it resolved before me please let me know what you did. Dennis van der Pool
I’ve the same problem… like many, many others on the Apple Support Communities.
