[SOLVED] Flickering pixels in HDMI monitor (but not on DP)

0BADC0DE · 2023-11-16 16:03:54

Hi all.
I have attached a second monitor (3840x2160) to my laptop HDMI port, while the first one (1920x1080) is attached, still via HDMI, on a USB3 docking station.
I have done this because I think that hi-res graphics over USB3 can eat more USB3 bandwidth. (Is this correct?)
Under some circumstances I still cannot reproduce the second monitor shows flickering pixles in a pattern similar to a die face with 5 dots: ":-:" .
Then if I move some window the flickering disappears.
If I connect the same to the docking station via DP and move the first monitor to the builtin HDMI, I don't have such a flickering.
For the records, I am not using WIFI (it is disabled) but a cabled ethernet to the docking station.
Any hint on how to fix this?

Last edited by 0BADC0DE (2023-11-18 19:35:29)

seth · 2023-11-17 21:35:17

I have attached a second monitor (3840x2160) to my laptop HDMI port … the second monitor shows flickering pixles

To be clear: 1920x1080 works fine on HDMI, 3840x2160 doesn't?
Signal. Cable - or the docks output.
Assuming this is xrandr:

xrandr --verbose # maybe we can still push down the signal a bit

3840 ×2160p @60Hz requires HDMI >= 2.0 and a "Premium High Speed" or "Ultra High Speed" <brief rant about the cringe having to write the marketing BS here> cable .
If you're at any limit w/ this, the dock in the middle might just be too much.

0BADC0DE · 2023-11-18 18:41:49

I am not sure whether the new HDMI cable is "Premium High Speed" or "Ultra High Speed" (I also hate marketing BS!), but swapping them actually fixed the issue.
So, both displays are connected via HDMI, but the "big one" (3840x2160) is using a cable "borrowed" from my kids Nintendo Switch.
The other one is a "normal" cable I have been previously using with the "small" one (1920x1080) which is still connected via docking station.

Thanks @seth.

P.S.
The docking station has 2xDP and 1xHDMI (as well as 1xGETH, 2xUSB2 for keyboard and mouse and 4xUSB3).
I think it should be OK as long as you have the right cables.

Last edited by 0BADC0DE (2023-11-18 19:36:17)

seth · 2023-11-18 19:32:19

Yup. The problem is (likely) that the the cable capacity is at its limites, so the slightly weaker signal out of the dock is no longer sufficient.

Please always remember to mark resolved threads by editing your initial posts subject - so others will know that there's no task left, but maybe a solution to find.
Thanks.

Arch Linux

#1 2023-11-16 16:03:54

[SOLVED] Flickering pixels in HDMI monitor (but not on DP)

#2 2023-11-17 21:35:17

Re: [SOLVED] Flickering pixels in HDMI monitor (but not on DP)

#3 2023-11-18 18:41:49

Re: [SOLVED] Flickering pixels in HDMI monitor (but not on DP)

#4 2023-11-18 19:32:19

Re: [SOLVED] Flickering pixels in HDMI monitor (but not on DP)

Board footer