MP 6,1 Mac Pro and LG UltraFine 5k screen flickering while using certain apps

[onelegend]

I have a MacPro 6,1 that's connected to a LG UltraFine 5K with an OEM Apple Thunderbolt 2 cable and an OEM Apple TB3 to TB2 adapter on the back of the monitor.

I have been doing some testing and I've found that there's flickering on the display when using Chrome and Edge.

I haven't found a single solution to this issue, even though there's compatibility listed on both LG and Apples website

I've checked for firmware updates, graphics card updates, etc... Is there something I'm missing?

I know the screen is fine since I connect it to my iPad all the time and don't experience flickering there

I also know that the Mac Pros graphics card is working fine since I use other monitors with it

Am I missing something?

 

[h9826790]

It seems like software issue from the browser. You may try to change some GPU related setting e.g. this one

and see if it helps.

 

[onelegend]

Disabling Hardware acceleration doesn't help the flickering unfortunately. If this were any other program, I'd be fine. 90% of my computer use is in browser though and Safari doesn't have some key settings I need.

 

[h9826790]

There are few more GPU related settings in the experimental settings. You may try them as well.

Anyway, if only browser has this problem. Then I think we can assume all associated hardware are fine. But just the browser's internal issue.

Just curious, Did you try full screen mode? Some bug may only happen in window mode. That may be a possible work around before you find the issue.

Other possible work around can be playing video in the background, etc.

 

[davidec]

What’s the refresh rate setting. If it variable? Try locking it to a lower refresh rate like 60Hz

 

[IconDRT]

Try running the display through HDMI on 6,1 and see if you still get flickering. I have a 6,1 with 8-core/D700s and I get flickering in the top right of the screen at random, not just with Chrome. When I run the display (also LG) via HDMI (which maxes out at 30Hz), flicker goes away. Seems some 6,1 have an issue with flickering despite various folks with identical 6,1/firmware/GPU some have flicker some don’t. One guy still had it even after Apple changed his GPUs. Some consensus that flicker began sometime after first Mojave update. I’ve reproduced the flicker on Mavericks all the way up to Monterey on my 6,1. There is no consensus on whether this is a driver issue or app issue or old/fatigued GPUs, power supply etc.

But there is some good-ish news. If you plug in a dummy HDMI into the HDMI port on the 6,1 (as if you were going to run headless - The HDMI dummy will show up as a second display) and mirror the primary display that’s plugged in via TB2-DisplayPort cable, then you can run the primary display at 4K/60Hz without the flicker. It has worked for some folks and has worked for me. I don’t recall the theory behind it, but speculation that maybe some variation in power to GPU and when you plug in the dummy HDMI, the GPU thinks its running more than one display and so amps up the power enough so that there is no more flicker. I may not be explaining correctly/technically but that’s the gist of it.

Here’s the thread I stumbled upon that helped me. Also, people experienced flicker with D300/D500/D700 so not specific to one card though seems the D700 more affected than others.

https://forums.macrumors.com/threads/mac-pro-6-1-12core-d700-flicker-issue.2217096/page-4?post=28346905#post-28346905