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

cltd

macrumors member
Original poster
May 22, 2014
65
11
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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chscag

macrumors 68040
Feb 17, 2008
3,360
1,065
Fort Worth, Texas
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
 

cltd

macrumors member
Original poster
May 22, 2014
65
11
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
Thanks a lot! Sad news... BTW I can't find ifixit tutorial on GPU.
 

profcutter

macrumors regular
Mar 28, 2019
119
47
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?
 

chscag

macrumors 68040
Feb 17, 2008
3,360
1,065
Fort Worth, Texas
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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cltd

macrumors member
Original poster
May 22, 2014
65
11
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.
 

CYB3RBYTE

macrumors 6502
Sep 2, 2014
338
114
Midwest
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.
 

cltd

macrumors member
Original poster
May 22, 2014
65
11
Thanks for advice, but can't find anyone reliable who can do that.