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Ive got a 27" iMac 4.2ghz i7, 16gb ram, 8gb GPU, running OSX 10.13.6

Ive got 2x external 1080p monitors connected to it via the thunderbolt ports using 2x of these HDMI to thunderbolt adaptors

Recently Ive been having allot of issues with all 3 screens, mostly to do with the order in which they are setup in system preferences > display > arrangement. I have the screens setup as follows on my desk from left to right : 1080p display, iMac 27", 1080p display. I originally arranged the screens like this in the arrangement tab, but every time the iMac goes to sleep the arrangement seems to randomly re arrange itself, so each time the computer is turned back on i need to reset it.

Yesterday i was having allot of issues with all displays, the iMac was displaying the image below (see attached), the far left screen 1080p wasn't working, and when it did it the other 1080p and the iMac screen would dim very dark. I swapped out the HDMI to thunderbolt adaptor, and it seemed to get all screens working, but they are still not saving their arrangement settings.

Any ideas what might be wrong here and how i can fix it ?

image of issue happening on screen

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2 Answers 2

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I wrote a tool called displayplacer that let's you describe your layout and re-apply that same layout. It will let you set up profiles for changing the resolution, rotation, and positioning of your monitors.

For example, he's my 4 monitor setup profile. I have this command tied to a hotkey using BetterTouchTool. displayplacer "id:A46D2F5E-487B-CC69-C588-ECFD519016E5 res:3840x2160 hz:60 color_depth:8 scaling:off origin:(0,0) degree:0" "id:F466F621-B5FA-04A0-0800-CFA6C258DECD res:1440x900 color_depth:4 scaling:on origin:(-1440,1437) degree:0" "id:4C405A05-8798-553B-3550-F93E7A7722BB res:1440x2560 color_depth:8 scaling:off origin:(3840,-363) degree:270" "id:18173D22-3EC6-E735-EEB4-B003BF681F30 res:1920x1200 color_depth:8 scaling:off origin:(960,-1200) degree:0"

It's also available via Homebrew brew tap jakehilborn/jakehilborn && brew install displayplacer

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That looks like a GPU failure and not any sort of software issue.

Have you tried making a new user account or does this garbled text happen at the pre-log in / pre boot screen?

Worst case, you would need to bring a second bootable OS to that Mac to be sure it's not the OS if you get clean graphics in the startup mode, but garbled once the OS takes control of the GPU and enables the standard rendering options.

If you can work with it normally before the image fails, make a new user account and make sure that new account has the issue before going to the trouble to make a second OS or erase/install.

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  • its strange because once the external screens where un plugged and re plugged, it worked fine. This morning it has woken out of sleep and the external displays work (apart from the arrangement being wrong). Ive only seen the "pink and yellow" screen once. Re, the GPU can the cache be flushed / the GPU be reset, would that even make any difference ?
    – sam
    Commented Jan 30, 2019 at 13:01

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