Mac Mini (M1) 2020, LG UHD monitor flickers on dark colours.

I have the exact same issue with a Macbook Pro M1 (2020) and an external Lenovo T34w-20 Ultra-Wide monitor.

FWIW, I just realized that changing the monitor color profile to "Custom", the problem is gone as long as I keep the "Blue" value at 98% or lower. Just like flicking a switch.

This will probably not work for everybody, but hopefully it will for some.

Hey all, after months of being annoyed by this issue on my 32" Dell 4K screen, found this thread and tried most of the suggestions, In the end the one that works for me is changing the screen color profile to "Image P3", and it was solved instantly, and if anything, the picture just looks clearer now, even when there's no condition that causes the bars and flickering.

Display flickers Solved

If you are using HDMI cable, You have to change this option to solve this problem. Click>system preferences>Display>Refresh rate> set to 60 Hertz. Check screenshot plz.

I’m only talking about the LG monitors specifically, but it’s interesting to hear that similar stuff is happening to other monitors.

my LG 32UN500 was flickering really badly on every setting, apart from HDR mode, and when I change the Black Level on the monitor in SDR mode. Both of these resolve it completely for me.

I was having the same problems as many of you are reporting here. I was able to get the monitor to stop flickering, but I'm not sure it's the ideal solution.

I have a Dell Dell U2718Q

It's connected via an HDMI to HDMI cable

If you go into the monitor settings and change the refresh rate to 30hz instead of 60hz. After doing this, I don't get any flickering. It's not ideal as I'd rather run at 60hz, but it beats having my screen flicker every few seconds.

The problem seems to have something to do with the refresh rate since I tested it at 50hz and still get the flicker, BUT it's a slower flicker and is different than the flicker I get when trying the 60hz setting.

Give it a shot and report back since I'd like to know if others are getting the same results as what I've gotten by changing the refresh rate.

i noticed that the flickering almost stop and doesnt happen much AFTER i stop using the build-in usb3 for attaching to any hard drives. i just use the USB-C connector and if i need to use USB 3, i'll use a USB-C to USB 3 hub and the flicker doesnt happen anymore, or less happening than before. im using the LG 32 550-w

From my tests with a multimeter just now I have one end directly connected to the earth in the mains socket (do not try this is you do not know what you are doing!) the other end probing the shield on the connectors on the back of the Mac mini. I notice that with the monitor unplugged via HDMI the Mac mini is 'floating ground' in other words resistance is very high between earth on the socket and earth on the shields of the USB cables still plugged in.

When I plug the monitors HDMI cable back in it grounds the whole of the Mac mini and resistance is low. This is because the monitor has a 3 pin mains cable with earth passing through to the HDMI sockets shield. It surprises me that apple does not ground the Mac mini directly this is the reason why when you touch MacBooks and run your finger across them you get a 'buzz' feeling as they are not grounded either. You and the MacBook have a potential difference to ground. Older MacBooks around 2011-13 came with a mains cable with the long cable attached to the brick which passed the earth ground through to the MacBook via the power brick. In the box there was also the small white adaptor that you could attach directly to the power brick shortening the overall length of cable , this thing didn't have a pass through ground. Crazy, in my studio this used to cause a slight hum which is how I found that out.

USB 3 devices can emit a lot of RF interference, grounding a cables shield which runs inside the length of the cable reduces RF so I think all these things are connected with the problem.

I have just updated to 11.2.1 so am going to wait until I see it happen again before I start disconnecting USB drives and like you say TechnicaStudios start using only the USB hub

I have the same problem with Samsung LU28E590DS/ZA 28" 4K Monitor connected through 4K HDMI Cable. My second monitor is identical and connected through the Thunderbolt port and it works just fine. The HDMI connected monitor flickers every so often and appears snowy when starting up.

Update: I went to the shop I bought the LG monitor. They tried my Mac mini with new LG monitor with the same model (24MK600M), it had the same problem. They then tried to connect a Notebook with my LG monitor, it did not have problem. So, they mentioned that, contact the shop that I bought the Mac mini M1.

So, I then went to the shop I bought the Mac mini M1. They tried a MacBook Air M1 (because they did not have any Mac mini M1 for demo) with my LG monitor, it had the same problem. So, they mentioned that, they will report the problem to Apple.

I then went to my friend office to try his Mac mini M1 with my LG monitor, it had the same problem. But my Mac mini M1 did not have problem with his Acer monitor.

I`ve got feeling it has something to do with timing and synchronization. If you set colour space to some wider kind (esp. SMPTE RP 431-2-2007 DCI (P3)) Monitor works almost flawless. If you encounter this flaw again, setting monitor sharpness to 0 helps again. If flaw still persist then manually degrading DP to 1.1 version helps again (you can choose between 1.1 and 1.2 on Philips monitor). Also setting monitor colour temperature from 6500 K to sRGB colour space helps again. Now I have eliminated the flickering vertical lines flaw in 99% of time. It occurs again if I try to lay some old lo-fi dark, lo FP, low resolution videos on Youtube. To me it feels like display is losing sync while colours are too dark. What about colour bit depth? How many bits per pixel is the graphic card vs the LCD panel? Those shivering vertical lines remind me of setting the trigger level bad on an oscilloscope. It feels to me like monitor cannot guess beginning of line. Most interesting is that downscaling or overscanning eliminates this problem 100% (set on monitor itself, not in system settings panel). So again!!! Dose monitor lose sync while there are large areas displayed in same bit depth on monitor while meant to be in different bit depths by the graphic card (using wider colour space helps)?

FWIW, I switched to a new USB-C — DP cable and, so far, it's been working fine for 24 hours. Naturally, as soon as I hit "Post" it will start going nuts again and flickering out to black every couple of minutes but for now it's working as expected.

I have to correct what I wrote yesterday. I retried the DP cable and after rebooting it seems to work much better with the DP cable than with HDMI. Only very light vertical lines. After setting the monitor from DP1.2 to DP1.1 it seems to be fixed for the moment and I can not see any issues right now.

Yes, I also did very similar tests and with good results, with the difference that instead of connecting a second HDMI port on my UHD monitor, I connected it to another small and simple FHD monitor and then changed my scaling settings by going into system preferences, Displays, and 'Option'+Clicking on scaled, and I set the scaled resolution to 2304x1296 on my UHD monitor. 

It solves the problem 90%, it happened to me again once in a week, very little. At least you can work more comfortably

MatejP84 wrote:

I have two monitors, one is USB-c-DP and other is HDMI-HDMI, the first one is also working flawlessly, but HDMI is the big pain...

Are you using an HDMI certified high speed HDMI cable? How long is it?

wirh hdr mode off. When I change the black level it fixes it.