Mac Studio M1 Ultra External Monitor Flickering

So tired of this....

Before anyone suggests that I read this or check that or change cable.... That has all been tried to death.

Apple M1 Macs have an issue with external monitor flickering. Period. Every OS update I wait in the hope that it gets fixed. Nope... Just did the update today and it flickered within about 2 hours.

In my situation I have 2 external BenQ monitors, 1 is 4k 32" PD3205U and the other (flipped sideways) is a 27" 1080p PD275Q.

The 32" is connected via a good HDMI cable and the 27" via a thunderbolt cable. Yes, I have tried MANY different cables)

I have a couple of external SSD enclosures in a Raid0 and another external SSD for backups. USB-C to DAC, and one or two other connections. Whether they are connected or not does not affect this.

Periodically, the 32" starts to flicker, mildly at first, then it may increase or stop entirely.

When you look closely at the pixels while this is happening you can see that alternate vertical rows of pixels are shifting. Reminds of old CRT monitors. It can flicker quite dramatically sometimes.

From what I can tell, this is NOT a 3rd Party hardware issue (cable or monitor). The issue usually happens when I am working in Photoshop or Illustrator and I am in the finder which usually consists of 2-3 large windows. The flickering comes out of nowhere. If I tab back to Photoshop the flickering may stop. Or, may not be as bad. Cycle through various apps and it usually changes. To me, the Finder is affecting this, or some part of the OS that is translating to the display.

BenQ have a page dedicated to the issue: https://www.benq.com/en-us/knowledge-center/knowledge/how-to-fix-mac-m1-m2-external-monitor-flicker.html

None of their suggestions nor anyone else have helped. There are tons of posts everywhere from Reddit to Macrumours to here that all raise the same issue (for the most part). Still.... no fix or no acknowledgement from Apple. Everyone says to change the cable or whatnot but it seems the issue persists for most of us.

I've been an avid Mac user since 1990 so I have an idea of how to troubleshoot these issues.

If anyone can give me any insight on how to resolve this I would be eternally grateful.

The odd thing is it tends to happen when I get very busy! Maybe it's picking up on my karma....

Mac Studio (2022)

Posted on Mar 26, 2024 11:46 AM

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Grif_ Author

Level 1

51 points

Posted on Jul 4, 2024 2:13 PM

Hey Grant,

so BenQ are aware of the issue. There’s a link to their response on the OP. They suggested various steps which I’ve gone through a few times with no change. What’s interesting is they mention to change the “image pattern” that triggers the flickering. So they too know that displaying some sort of pattern causes the issue.

I had it hooked up to my MBP with no issues. It’s an Intel though.

I’ll have another look through the monitor settings but fairly sure I have it set for standard sRGB. No gaming settings that I can see

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44 replies

Aug 31, 2024 12:39 PM in response to Grant Bennet-Alder

Alright, with that in mind, here is a link to a Certified Cable. Will that one resolve the issue? It is 6.6 feet, but certified to transmit 40gbs. If I'm understanding correctly, no adapters should be used except the cable itself it sounds like. Since virtually no monitors besides apple's own monitors are thunderbolt capable, this leaves a lot of room for improvement on clarity for customers.

Grif_ Author

Level 1

51 points

Sep 10, 2024 4:15 AM in response to Grif_

Another day another flicker!!

What's setting it off today is a Google Chrome window with mostly black content.

This is driving me nuts and I'm not sure what to do at this point. I'd get rid of my BenQ 32" and get another make if I thought it would resolve the issue but most say it's not BenQ related.

Grif_ Author

Level 1

51 points

Oct 18, 2024 8:59 AM in response to Grant Bennet-Alder

Hi Grant. I did try .5M TB4 cables. Same issue.

This also did not happen on any other Mac I have, MBP 2019 and a MacPro 2019, both intel. They work fine with the other cables I have. I guess Apple Silicon seems to treat this differently. Judging by similar posts in other M1/2 related discussions.

It was also a massive pita to troubleshoot. If it is the case that Apple silicon Macs require very specific cables to work with some 4k monitors this should be made clear. Somewhere. Either the monitor manufacturers or Apple. It also does not seem to be consistent. Some folks have the issue, some don't.

In my case, lesson learned I guess. :-)

Thanks for all your input.

Oct 18, 2024 11:15 AM in response to Grif_

A 0.5 Meter Thunderbolt cable SHOULD have worked error-free. I don't know what went wrong there. Perhaps that still ran into the festering BenQ issue.

An important distinctive feature of the Apple-silicon M-series Macs is their tremendous memory bandwidth, which is likely to be increasingly important as users find ways to use it all up and more. That bandwidth gives Apple-silicon Macs the ability to produce screen data streams that are completely relentless -- no dead times in between packets or screens to give peripherals time to recover.

As for BenQ, It sounds like older systems paused a little between packets and between screens, and BenQ had been counting on those little pauses, taking advantage of that extra time rather than meeting the EXACT specifications. Thus, a hardware change (no way to know how extensive) was required to eliminate the corner-cutting and bring it up to conformance with the exact spec. (Clearly if Apple were operating beyond the actual spec, BenQ would be protesting loudly about it.)

Regarding older Macs, what readers are generally finding is that more recent versions of MacOS are increasingly demanding in seeing NO transmit errors. if your older Macs are running older versions of macOS, they may not be complaining, simply because they are not checking so carefully.