GameMode not working with HDMI 2.1 (RTX 3090),Samsung 2020 QLED [1402] Update !!!!!!

[RouDeR]

Background:
TV is 75 inch Q800T (EU version), but I assume this will affect all of the 2020 Samsung TVs
Software is version 1402.6 (updated Octomber 8th)
HDMI Cable 2.1 certified full 48gbps
The same HDMI cable works just fine with HDMI 2.0 GPUs like my old GTX 1080Ti (Game Mode works flawlessly there)
Current GPU:  RTX 3090 with latest Nvidia drivers

What is working as intended when using the HDMI 2.1 port and RTX 3090 as a source::
* Outside of game mode I don't have any problems, I can run at 4k@120hz RGB 10 bit or 8k@60hz 4:2:0 10 bit without any problems.

What does NOT work when using the HDMI 2.1 port and RTX 3090 as a source:
* If you turn on Game Mode, the TV picture goes BLACK and it looses signal
This happens disregarding on what resolution and refreshrate you are playing, I`ve tried the following:
- 1440p@60hz Input Signal Plus ON
- 1440p@60hz Input Signal Plus OFF
- 1440p@120hz Input Signal Plus ON
- 4k@60hz Input Signal Plus ON
- 4k@60hz Input Signal Plus OFF
- 4k@120hz Input Signal Plus ON

- 8k@60hz Input Signal Plus ON
NONE of them was able to switch to Game Mode !!!

However
If the RTX 3090 is connected to one of the HDMI 2.0 ports of the TV, Game Mode is perfectly functional, but then you are restricted to 4k60hz and 8k@30hz

SUMMARY:

Spoiler

Game Mode does not work AT ALL on the HDMI 2.1 port when HDMI 2.1 source is Attached.

[RouDeR]

It is not from the cable it is either from TV software or Nvidia software,

This brightness flickers is happening to me when I`m in range 80-110 FPS in some (not all games), game that this issue happens for me is Elder Scrolls Online.
I have 3 different brands HDMI 2.1 cables with different length (3m,2m,1.5m) it happens with all of them.

[shadowsheikh]

Having a similar problem. I'm running a 55Q90T off of my ASUS TUF RTX 3090. Enabling game mode causes the TV to lose signal with the PC.

With game mode off, it functions perfectly fine as a second monitor. 4k, 120hz and HDR all work together after enabling them from the NVIDIA and Windows settings.

[Shaun400]

Same issue here with 55 inch Q70T and RTX 3080

[wickfut]

I have a RTX3090 and Q700T which used to work until about 10 - 15 days ago, now I can't even turn Input Signal Plus on to get to 8k as it gets a No Signal Error and sometimes crashes/restarts the PC. 

A work around I've discovered is 

Get a Display Port to HDMI adapter. Connect the PC to the TV via the DP adapter.

Set the graphics settings to 4k, 60hz, 4:2:0, 10 bit, Limited

Switch on game mode / Input Signal Plus

Turn the TV off. 

Swap the cables to the HDMI socket on the GPU

Turn the TV back on again. 

You can now turn on game mode / Input Signal Plus / 8k resolution. 

Issue - I lost the ability to use 1440p and 1080p, which can be solved by setting the scaling to the GPU rather than the display in the GPU settings, also I usually need to go through this whole cable swapping process each time I update the GPU drivers. 

I have been in contact with Samsung via Facebook and phone for the last couple of days trying to sort this. I've had them connect to the TV via remote while they reset the EDID on the TV with no luck.
An engineer is coming out in the new year to look at the TV so I'll update then. 

I believe it's the latest firmware causing this. My PC stopped working correctly around the time I updated it to 1460.09  

[Denn15M]

on My q80T 55 and i was having this issue as well, on the newest firmware as well. you can see a video of what was happening here. this is my video i made. https://www.youtube.com/watch?v=yRSvigGwadU&t=4s

The issue happens even when not using game mode as well but to a less of a degree, once you turn on 120Hz 4K it starts in any mode. If you lower your colour mode to 4:2:2 it still occurs as well on port 4 but not on port 1-3 which are 2.0

Interestingly you can use one of the other 3 HDMI ports which are 2.0 ports and you can get 4K 120Hz to run but you just have to lower to 4:2:2 but this makes the colours look really bad as well(more than the loss of depth attributes normally) for some reason like its not displaying the colours correctly (another issue i suspect)
VRR is totally broken as well and has flickers across the whole range even when using 1440P, in general these TVs are junk and have so many issues for gamers they are not worth considering. 

Samsung kept denying it was a issue to me, replaced my motherboard on TV and issue was still happening, then advised me to, quote: "Don't use game mode" or my favourite "Upgrade my 3070 to a 3080". Their support was really bad and they didn't want to admit it was a issue even though it happens on multiple video cards and the Xbox series X as well for me. in the end i had to return it to the shop because their support was making me dance around again and again for no reason and wouldn't even acknowledge the problem was there and kept blaming me for it.

They are stalling everyone for a Firmware update by the sounds of it, but i doubt they will fix it in FW, this looks like a inherent hardware issue like the chip issue on the Audio Receivers that is occurring now.

[Denn15M]

look at my comment below mate, as you are about to experience what i had happen. the Tech coming out will replace the motherboard and thats it, they will then direct you to speak with Samsung support again. 

They will then continue to blame your device or you and its not their tv at fault. this won't be fixable by FW as its a hardware level issue that is happening on all their models and HMDI 2.1. you should check what other Brands and models your shop has and try and return for another brand as All Samsungs have this issue.

[wickfut]

It worked perfectly until a few weeks back. Something either broke with the firmware or broke with the hardware. 

1440p in game mode had tearing, now I can't even get any resolution under 4k to work in game mode - I just get no signal errors. 

I can live with it the way it is, but I don't want to. I use it as a PC monitor in a audio workstation (as well as gaming) so needed the extra image scaling. I run Cubase @ 6k and on the TV it scales and looks clear, while scaling on the GPU is a mess. 
The only other 8k TV in the price range is an LG Nano956 55". No reviews online, can't find user feedback when used as a monitor. Reports of low contrast ratio and terrible backlight. Not sure what to do. 
I sold my KS7000 which was working perfectly and had great black levels. Can't find anything at all to match it now days. Can't go OLED due to burn in. 

[Eran9998]

Please let us know!

[Denni5M]

You can get around most of the issues if you setup custom resolutions for the ones that are broken and just set the colour mode to something lower, with that I was able to get stable 4k 120hz and all lower resolutions as well.  make sure you have the Signal plus enabled as you can't get the high bit rate res/refresh combos with it off. The problem is we paid for a TV that is meant to support gaming features like VRR and 120hz 4:4:4 4k but it doesn't so it's really junk for gaming on. 

[wickfut]

I don't get that option.  Mines a 60hz 8k TV not a 4k 120hz TV.