Resolved HDMI monitor flickers after Mojave update

[Simon R.]

Not sure if this is a Mac Pro or Mojave issue or a combination but let me try to explain.

After updating my cMP from Sierra to Mojave, my third monitor (which happens to be a Samsung TV) that is fed from the HDMI output from a Radeon RX 560 card no longer works properly. The display is turning on fine, but after a second it goes black, then back on. Then stays on for a few seconds, goes black again etc.

Just to be sure it isn't a connection issue, I booted into my old Sierra partition, and sure enough, the display works fine.

Any clues? This is really annoying and if this can't be fixed I will be forced to remain in Sierra, but I really would love to go Mojave because it has some Audio Units 3 features that I look forward to.

 

[h9826790]

Sierra only support up to HDMI 1.4

Mojave support up to HDMI 2.0

Most likely your setup (may be the cable) is not good enough for HDMI 2.0. And the system trying to output HDMI 2.0 which eventually cause the trouble.

You may use ResXtreme etc to set the output back to 4K 30Hz or below.

 

[Simon R.]

Sierra only support up to HDMI 1.4

Mojave support up to HDMI 2.0

Most likely your setup (may be the cable) is not good enough for HDMI 2.0. And the system trying to output HDMI 2.0 which eventually cause the trouble.

You may use ResXtreme etc to set the output back to 4K 30Hz or below.

Thx but its just a 1080 monitor. I can chance it to 24 or 30hz but it makes no difference. And the cable is plenty good for HDMI 2.0. So that isnt it.

 

[h9826790]

Thx but its just a 1080 monitor. I can chance it to 24 or 30hz but it makes no difference. And the cable is plenty good for HDMI 2.0. So that isnt it.

Try 1080i output then.

 

[Simon R.]

Try 1080i output then.

Nope. Its not it. Something changed in mojave regarding hdmi. There are several threads about this problem already. Both on mac Pro and especially on MacBooks. Problem is probably related. Seems all I Can do is hope that Apple fixes it in an update.

 

[h9826790]

Nope. Its not it. Something changed in mojave regarding hdmi. There are several threads about this problem already. Both on mac Pro and especially on MacBooks. Problem is probably related. Seems all I Can do is hope that Apple fixes it in an update.

You mean 1080i option is not there? Or nil help?

 

[Simon R.]

You mean 1080i option is not there? Or nil help?

I was a bit too quick there. Actually changing to 1080i seems to work! Image looks less sharp though, but it's better than no image. Thanks for the suggestion, I hope this solves the problem. I am pretty sure it used to work in 1080p in Sierra though so it doesn't really make sense.