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Hi, I have been having an issue with my computer today. It starts up fine and seems to function normally. After a while the screen shifts or flickers or turns white randomly (or all of the above). After that the computer shuts down and restarts. Any idea what the problem may be? Thank you, Colin C Update (02/18/2019) I’m aware of the graphics card issue and replacement program. I had this issue dealt with a few years ago and my computer has been working fine up until this point. I ran terminal as suggested by Jonah. One of the previous shutdown causes is -128. The shutdown cause list suggests that it’s “probably GPU related”. What do you guys suggest is the best course of action ? Thanks for all your help!
Ouch! I’m suspecting your dedicated GPU board is going on you. Give this a try reboot your system and press and hold the Option (⌥) key is the screen stable then? You might also try running diagnostics as well Reference: Mac startup key combinations Update (02/20/2019) We don’t have a direct GPU board guide but this will get you 90% there Installing iMac Intel 27" EMC 2429 Dual Drive Kit (HDD or SSD) follow it to Step 33, pop off the SATA & power cables for the HD & optical drive, as well as the boards power connector so you can fully remove the logic board, carefully ease it out. Once the logic board is out flip it over to locate the GPU thermal sensor
Remove the screw holding the heat sink to the frame
Then remove the four screws on the board
Carefully lift the heat sink off Your system came with either a MXM-A or MXM-B board
Remove the two last screws holding the board in and ease it out of the socket. Here are your choices for replacement boards: AMD Radeon HD 6770 512 MB - P/N 661-5967AMD Radeon HD 6970 1 GB - P/N 661-5968AMD Radeon HD 6970 2 GB - P/N 661-5969 You might be able to recover the board by heating the board up to fix the cold solder joints that develop. You’ll need to apply some flux onto the board and using a heat gun heat up the board so the solder re-flows but don’t go to far! As you don’t want the components to shift. Some people just cook the board, I’ve found that technique is not as dependable as doing it properly. Here’s a time-lapse of someone using the heat gun approach YouTube - GPU Repair You’ll also need to clean off the old thermal paste & thermal pads, and will need to put fresh thermal pads on the RAM chips (don’t use thermal paste).
Holy Smokes! My computer has come back from the dead. I cleaned up the GPU and chips of the old thermal paste, baked it in the oven at 400F for 10 mins. I applied Arctic MX-4 to the GPU and K5 Pro to the chips. It works and I’m stoked!
It sounds like a graphics card issue. It was a pretty common issue with 27” iMacs in 2011 with an AMD Radeon HD 6970M, so that’s what I’d lean towards especially if that’s your GPU. The instructions in this guide can show you exactly why your computer is shutting off and would help us troubleshoot further. If it does end up being a GPU issue, it’ll just need to be replaced.
If your serial number ends with one of these designations DHJQ, DHJW, DL8Q, DNGH, DNJ9, or DMW8 DPM1, DPM2, DPNV, DNY0, DRVP, DY6F, F610 Your machine was part of an extended GPU card replacement program, which has now expired https://9to5mac.com/2013/08/16/apple-ope…
