20m hdmi 2.1 certified cable + LG 32GS95UE-B

[mnikitas]

Hi,

I am struggling to identify the root cause of the random instant screen on/off on resolution 4k@120Hz with ASUS 3080 with HDMI 2.1 port.

With the same cable and monitor but with Sapphire Nitro+ 5700 XT connected to its HDMI 2.0b on resolution 4k@120hz everything works without any problem.

With the same cable and ASUS 3080 and LG G1 65inch tv on resolution 4k@120hz everything works without any problem.

I was testing various parameters through CRU excellent tool but no luck. If there any way to troubleshoot the behaviour?

The cable is HDMI 2.1 20meter optical certified and I have already tested to use HDMI 5v voltage inserter through USB3 port but no luck.

Thank you so much for your time,
Mike

[ToastyX]

That has to be a signal quality problem. 20 meters is very long. Have you tried testing with a shorter cable just to make sure it isn't a monitor issue? The LG TV might have better error handling, or it might be using a lower FRL rate. Also HDMI 2.0 with the 5700 XT can only do 4K @ 120 Hz with YCbCr 4:2:0, so that uses half the bandwidth, and that would use TMDS instead of FRL. You can adjust the FRL rate in the HDMI 2.x data block in the CTA-861 extension block. 4K @ 120 Hz would only need 32 Gbps at 8 bpc, but 10 bpc + HDR would require 40 Gbps.

[mnikitas]

Thank you for the reply. With the short hdmi 2.1 cable (2m) there is no problem at all. With the 20m cable, I managed to have a stable connection at 2560x1440 120Hz 8bit YCbCr444 HDR but I have not yet understood if now I am using CTA-861 and if yes, how to calculate bandwidth with this resolution. I have already ordered a HDMI MPO (pure fiber) to solve the bandwidth limitation of the cable. I tried 4k@120Hz and minimize the FRL rate in the CTA-861 but I continue to have issues...

(03-05-2025 06:28 PM)ToastyX Wrote:  That has to be a signal quality problem. 20 meters is very long. Have you tried testing with a shorter cable just to make sure it isn't a monitor issue? The LG TV might have better error handling, or it might be using a lower FRL rate. Also HDMI 2.0 with the 5700 XT can only do 4K @ 120 Hz with YCbCr 4:2:0, so that uses half the bandwidth, and that would use TMDS instead of FRL. You can adjust the FRL rate in the HDMI 2.x data block in the CTA-861 extension block. 4K @ 120 Hz would only need 32 Gbps at 8 bpc, but 10 bpc + HDR would require 40 Gbps.

[mnikitas]

I bought an HDMI MPO cable 20m and the problem persists with LG 32GS95UE-B. I really cannot understand. LG TV G1 works fine at 4k@120hz with HDMI MPO cable. Any ideas?