After having the time to run through a full troubleshooting sweep from beginning to end on the "best" cables I have, I ended up at the same exact behavior as before. I launched a Steam game called 30xx for the first time, and--out of curiosity--tried bumping the resolution up to max 4096x2160. And it WORKED, although it did switch to 60Hz. Verified with LG CX that it was detecting 4096x2160 at 60Hz. I launch an old game like Dying Light and try the same thing, it drops the resolution down to 1024x768.
 
This is a SOFTWARE issue [probably].
 
This is either a nVidia driver issue or a Windows issue. Not my @#$*& cables, not the @#$*& 3080Ti, and not the @#$*& CX. Edit: wishful thinking
Also switched back to my Monoprice optical cable, because light isn't affected by EMI.
 
Note: nVidia rolled back the latest available driver for some reason (471.96 to 471.68) between the last couple days. I'm running 471.68 now. Edit: 471.96 is showing up again. I'm a little concerned that just yesterday going through the same navigation on the site brought up a different driver..but it hasn't made a difference either way.
 
Update: Playing Valheim on Vulkan drivers was not successful, but switching to a higher resolution saved the resolution in-game (4096x2160), and the LG CX verified that the resolution still remained at 2560x1440 @120Hz.
 
20xx yields the same result as 30xx (same developer, perhaps same engine), with full resolution at 60Hz capability. Haven't been able to find a way to test 120Hz yet. Edit: Explained by latest discovery that Windows Display Properties now allows switch to higher resolutions at the same color settings, though locked to 60Hz.

rgspro

GloriousCow
I know this is a 3090 thread ostensibly, but I'm having similar issues as others with my 3070ti
 
if HDMI Deep Color is enabled, I get NO SIGNAL. Unfortunately this setting seems to lock out higher refresh rates and PC resolutions also.
I was prepared to blame the cable, until I unplugged my DP monitor and immediately the display popped up on the TV like magic. EVERYTHING worked. , VRR, 10bit, 444.  I shed a little tear.   Plug the DP monitor back in and immediately NO SIGNAL on the hdmi.
 
When both are connected I don't even see the TV in Change Resolution, although it is there under "Set Up Multiple Displays," but unchecked.  I can check the LG, and hit accept, but about 3 seconds later it un-checks itself.
 
So right now I can use the TV for gaming if I unplug my monitor, but that's a bit annoying. I was told by several people that it shouldn't be any issue running both.  It can't still be an issue with the cable if it works fine without the monitor, can it?
 
Card: 3070Ti FTW3 ULTRA
Monitor: ACER XB271HU
Cable: Feizlink 40ft Fiber 8k
TV: LG CX 65"
 
~~~~~~~~~~~~~~~~~~~
Edit:
I seem to have gotten both displays working, and so for anyone who searches for this thread in the future, here's what I did:
 
- Make sure the HDMI input for the PC is set to PC in the home screen, under edit.  I'm not 100% sure this is required, but I'm doing it anyway as it is often mentioned
- Enable HDMI Ultra Deep Color for the input. Note that you now have No Signal.
- Back on your PC, set your resolution of your DP monitor as low as it will go.  We're talking 1998 here, 1024x768, refresh rate 60hz.  The TV signal may suddenly pop up at this point.
- Go to "Set up multiple Displays" and check the LG TV.   If you didn't set the resolution low enough, the screen may blink after a few seconds and the check box will un-check itself. 
- Once both are checked, you should have access to the LG TV display under "Change Resolution", and see a 4k @ 120Hz option under the 'PC' section of your resolution list.  Apply evertyhing you want, enable gsync, etc.  
- Once the TV is set, set your DP monitor back to native res/refresh.
- You may be working now
- You may have to repeat these steps if you unplug the cable or either the monitor or TV loses power completely :(
 
In any case, I can't blame the cable at least.  This is a less than ideal user experience, hopefully a future driver update smooths this bug out.
 

THANK YOU SO MUCH!
None of the Reddit threads say you need to scroll down and give the TV a "PC" resolution to enable 3840x2160 @ 120hz!

Yes setting the input type to PC is absolutely necessary, and to top it off, sometimes when the tv does firmware updates, it will change that setting for some reason.  I learned this the hard way, suddenly having resolution problems and eventually figured out that the firmware update for the TV had changed it.  As soon as I set it back to "PC", everything was fine again.  Just posting this so people are aware so if things go haywire after a firmware update, they know to check it.

A3roflux
After having the time to run through a full troubleshooting sweep from beginning to end on the "best" cables I have, I ended up at the same exact behavior as before. I launched a Steam game call 30xx for the first time, and--out of curiosity--tried bumping the resolution up to max 4096x2160. And it WORKED, although it did switch to 60Hz. Verified with LG CX that it was detecting 4096x2160 at 60Hz. I launch an old game like Dying Light and try the same thing, it drops the resolution down to 1024x768.
 
This is a SOFTWARE issue.
 
This is either a nVidia driver issue or a Windows issue. Not my @#$*& cables, not the @#$*& 3080Ti, and not the @#$*& CX.
Also switched back to my Monoprice optical cable, because light isn't affected by EMI.
 
Note: nVidia rolled back the latest available driver for some reason (471.96 to 471.68) between the last couple days. I'm running 471.68 now.
 
Update: Playing Valheim on Vulkan drivers was not successful, but switching to a higher resolution saved the resolution in-game (4096x2160), and the LG CX verified that the resolution still remained at 2560x1440 @120Hz.
 
20xx yields the same result as 30xx (same developer, perhaps same engine), with full resolution at 60Hz capability. Haven't been able to find a way to test 120Hz yet.

 
Set the hdmi input type on your tv to “PC”. This is done through the tv’s home screen Not the PC.

mizzer
 
Set the hdmi input type on your tv to “PC”. This is done through the tv’s home screen Not the PC.

I appreciate the point, but that setting has been on since Vincent Teoh (youtube reviewer) went over the settings of the LG CX last year. It's difficult to forget about it because I have to change it back every time I unplug an HDMI cable. With my 1080Ti and PC mode on, I was able to run 4K 60Hz HDR with RGB/Full. Unfortunately, the 3080Ti doesn't want to keep RGB / Full (10-bit) with a resolution higher than 1360x768--at least not in the NVCP.

A3roflux
I've been fighting to get a decent resolution from my 3080Ti for a week or so now. Gone through a bunch of "certified" cables with the same horrible behavior. Most any high resolution will cause the screen to black out a few times (blinking) and shoot straight to 1024x768. The behavior seems to hinge on the color settings for the most part.
 
If I set Output Color Format to 4:2:2 and Output Color Depth to 10-bit, I can get as high as 2560x1440 @120Hz. But the moment I try to switch to RGB (full or limited), the resolution will not go above 1360x768, most likely because all other resolutions above that (under the PC category) are 100Hz/120Hz only. What's even weirder is sometimes the NVCP will ignore a color setting I set, or switch to 12-bit Output Color Depth when I didn't touch the color and try to switch resolutions. If I switch out of 2560x1440 @120Hz by trying a higher color setting or resolution, I won't be able to get back to 2560x1440 until I restart the PC.
 
Cables I've gone through:
Phoossno Certified 8K Fiber Optical HDMI 2.1 Cable Ultra High Speed HDMI Cable 48Gbps 33ft 10m 
Monoprice 8K SlimRun AV Ultra High Speed HDMI Cable 30ft - AOC 48Gbps Black
8K HDMI Cable 10FT, Maxonar (Certified) 48Gbps Ultra High Speed HDMI 2.1 Cord 8K60 4K120 eARC
RUIPRO 8K Certified HDMI 2.1 Cable 10ft Ultra HD High Speed 48Gbps 8K@60Hz 4K@120Hz Dynamic HDR eARC HDCP 2.2/2.3
Zeskit Maya 8K 48Gbps Certified Ultra High Speed HDMI Cable 16ft CL3 In Wall Rated, 4K120 8K60 eARC HDR HDCP 2.2 2.3 <---currently running 2560x1440 @ 120Hz (4:2:2, 10-bit) on this cable
 

Is the shortest cable you have 10FT? Anything shorter in the 6FT or less range even if it is an older cable?
 
Other thing, what is the Prevent Input Lag set to in the gaming menu? Standard or Boost? Try Standard if it was on boost.
 
If you leave the color profile mgmt to auto and only change resolutions on TV or PC, does it let you go to 4k/120?
 
Were you running 4k 60 on your 1080 ti with the same cable? If so, could be the 3080 ti unless you can easily swap it out for another to test.
 
Edit: Saw the date after the fact - I presume you resolved this.

So I'm going to tie onto this thread as well.  I recently got a 3080 that I'm trying to get running with my LG C9 and I'm running into the same type of "no signal" issue noted in this discussion.  After much trial and error, I managed to get 4K/60Hz and 1440p/120Hz running, but now I have a new and very strange problem that is happening.  Many games and even 3DMark are unable to claim full screen mode if I am running at 1440p/120Hz mode.  If I switch to 4K/60Hz, there is no issue, but then I am unable to get 120Hz working.  Did anyone run into this specific issue I am describing?  It does seem to be related somehow to the 120Hz refresh rate and how some games are handling it.  For example, F1 2021 works just fine, as does say Age of Empires 4, but FIFA 2021 for example will not go into full screen mode at all.  An older game called Trine (specifically Trine 3), explicitly requires me to set the refresh rate to 120Hz otherwise the game crashes with a D3D error because it cannot claim full screen mode, yet once set to 120Hz, it claims it just fine.  3DMark crashes with a D3D error because it cannot claim full screen mode as well, and the only way to make it work is to switch to 4K/60Hz which magically makes it work again, but no 120Hz refresh rate.
 
Any thoughts?

3090+lg cx here

I turn off the TV when not in use, the problem is that sometimes it doesn't come back on. PC is running but TV won't come back on. Only the TV is connected over hdmi 2.1 cable
Zeskit Maya 2.1 8K HDMI Cable 6.5ft 4K120Hz 48Gbps for eARC Soundbar Ethernet Gaming 144Hz Certified Ultra High Speed HDR VRR HDCP 2.2 2.3 Compatible with Dolby Vision Atmos Apple TV Xbox Series X PS5

Always turns back on after restart. Fast boot is off, problem still persists. It happens very occasionally. Maybe once or twice a month?


Latest thing I tried was (found here: https:// www . reddit . com/r/OLED_Gaming/comments/m4dnrg/does_this_happen_to_anyone_else_black_screen_on/grdn4lc/ ) :

Nvidia Control Panel:  3D Settings > Manage 3D Settings > Global Settings > Power management mode: changed it from Normal to Prefer Maximum Performance

I will report if the problem comes back.

piptik
3090+lg cx here

I turn off the TV when not in use, the problem is that sometimes it doesn't come back on. PC is running but TV won't come back on. Only the TV is connected over hdmi 2.1 cable
Zeskit Maya 2.1 8K HDMI Cable 6.5ft 4K120Hz 48Gbps for eARC Soundbar Ethernet Gaming 144Hz Certified Ultra High Speed HDR VRR HDCP 2.2 2.3 Compatible with Dolby Vision Atmos Apple TV Xbox Series X PS5

Always turns back on after restart. Fast boot is off, problem still persists. It happens very occasionally. Maybe once or twice a month?


Latest thing I tried was (found here: https:// www . reddit . com/r/OLED_Gaming/comments/m4dnrg/does_this_happen_to_anyone_else_black_screen_on/grdn4lc/ ) :

Nvidia Control Panel:  3D Settings > Manage 3D Settings > Global Settings > Power management mode: changed it from Normal to Prefer Maximum Performance

I will report if the problem comes back.

Also try long pressing the power button. With the LG CX (now retired for a Samsung S90C), I had that happen every once in a while. The long press on the power button hard restarts the TV and got the picture back for me with my 3090 FTW3/4090 FE.

arestavo

Also try long pressing the power button. With the LG CX (now retired for a Samsung S90C), I had that happen every once in a while. The long press on the power button hard restarts the TV and got the picture back for me with my 3090 FTW3/4090 FE.





on the remote or the tv?

it happened again, so i came back to this thread, lol. it's very rare yet so annoying

piptik

arestavo

Also try long pressing the power button. With the LG CX (now retired for a Samsung S90C), I had that happen every once in a while. The long press on the power button hard restarts the TV and got the picture back for me with my 3090 FTW3/4090 FE.

on the remote or the tv?

it happened again, so i came back to this thread, lol. it's very rare yet so annoying





On the remote.