Any ideas?

[PrinceVlad]

Hi guys

I bought a 21,5 inch Imac a while back. I got it with Catalina already installed.

It has this intermittent problem where I would get glitches on the screen and artifacts (see pictures).

It will be fine for a while and then come back. If I select reduce transparency it's a lot better. For stuff like Chrome, Firefox and other apps I turn off Hardware Acceleration and they are fine.

I removed MacOS and installed Linux which runs without the problem, but there you have problems with wifi.

I then booted into recovery and it installed Mountain Lion which it originally came with. With Mountain Lion there are no issues. I upgraded to Sierra, once again no issues. Once upgraded to High Sierra the problems return.

I suspect it's the GPU, but the fact that it's fine with Linux and previous versions of MacOS baffles me.

It's really not that bad, but it messes with my OCD

I've put it up to trade now for a laptop, but I would really like to know what the problem is and maybe solve it.

Any ideas?

 

[DapperDanMan]

iMac caught iCorona? Put it in a box and leave it alone for two weeks.

 

[Lord Flacko]

Have you run diagnostics ? Are you able to replicate the fault in safe mode ?

Use Apple Diagnostics to test your Mac - Apple Support (ZA)

Apple Diagnostics, formerly known as Apple Hardware Test, can check your Mac for hardware issues.

support.apple.com

 

[PrinceVlad]

Have you run diagnostics ? Are you able to replicate the fault in safe mode ?

Use Apple Diagnostics to test your Mac - Apple Support (ZA)

Apple Diagnostics, formerly known as Apple Hardware Test, can check your Mac for hardware issues.

support.apple.com

In safe mode it's gone. I've finished installing Catalina again. Installed Chrome and Spotify. On both the effects appear when hardware acceleration is enabled. Once disabled it's gone.

So wherever possible I disable hardware acceleration. I switched of animation and reduced motion. This is all makes it happen a lot less.

 

[Lord Flacko]

Run diagnostics, if there's an issue with the GPU it might pick it up. Unfortunately the extended diagnostics can only be run at an Apple Authorized Service Provider (iStore or Digicape).