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iMac 27" late 2013 - stucks on Apple logo while booting; distorted graphics, green artefacts

C

cltd

macrumors regular
Original poster
May 22, 2014
137
32
Hello,
Please, help me diagnose this problem with iMac 27” (late 2013; NVIDIA GTX 775 XM). iMac stucks during the startup:
- OS doesn’t load. Loading bar stucks in the middle or so.
- What’s more, loading bar is distorted, with green artifacts.
- All those known startup shortcuts don’t work (verbose mode, recovery, single user etc.)
- Works only single user verbose mode, but frankly saying I don’t know what can I do here.
- As usual, hardware test says everything is OK.
- I have bootable backup on external drive, but it doesn’t load, it stucks same as internal drive.
- iMac starts under Ubuntu in safe graphics mode, but GUI is distorted (again, green lines everywhere).
- I can use iMac as target drive.

Is my GPU failing? Has anybody else had this problem?
 

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It sure looks like a failing GPU and all the symptoms you describe also indicate that it's a GPU problem. A late 2013 27" iMac has its GPU on a separate card but it's very difficult to get at it. You can google for various fixes. Also take a look at the replacement procedure on ifixit. www.ifixit.com
 
chscag said:
It sure looks like a failing GPU and all the symptoms you describe also indicate that it's a GPU problem. A late 2013 27" iMac has its GPU on a separate card but it's very difficult to get at it. You can google for various fixes. Also take a look at the replacement procedure on ifixit. www.ifixit.com
Click to expand...
Thanks a lot! Sad news... BTW I can't find ifixit tutorial on GPU.
 
When I read the tear down for the 2013, it didn’t look like it had a replaceable GPU. You sure it can be replaced?
 
I think that ended with the 2013 model. That’s when the enclosure got thinner.
 
I did find this YouTube video
but it may be for a previous version iMac. In any event, even if you have to replace the logic board (in case the GPU is soldered in) the instructions at ifixit are quite extensive.
 
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Got info from repair service: GPU is unrecoverable, need to buy whole main motherboard, which costs ~40% of the new machine. It's uneconomical, so iMac will be sold for parts.
 
Have you tried reaching out to any local shops to see if they will try a reflow of the GPU solder points for you? Could possibly bring it back.
 
Thanks for advice, but can't find anyone reliable who can do that.
 
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