bigfatfluffycat
So I've had my CX for a few weeks and had it paired with a TUF 3080. I was able to get everything setup to work perfectly at 4k120 and its been jaw dropping. I just upgraded to an EVGA 3080ti FTW3 and now I'm experiencing the "no signal" issue when turning on the "ultra hd deep color" setting. I can get 4k60 to work fine, but the second I switch the ultra hd deep color setting on to be able to get 4k120 the tv goes to no signal. I've double checked everything, tried suggestions from multiple other posts with the same issue and I cannot for the life of me get it to work. What else am I missing here? Any help on the matter is appreciated. 

I'm not sure if this will help, but just in case:

Presumably you've set everything up in the way mentioned in the opening post of this thread?
 
And in the "Home Dashboard" menu in the TV, you set the HDMI input type you're using on the TV for your PC to "PC"?

Thanks for the info. Yes, I went through the different steps a bunch of times. Finally was able to get it to work. Had to remove and re-add setup multiple displays option in Nvidia Control Panel. (I had tried it before with no luck) Getting 4k120 setup can be a pain but its definitely worth it once its working properly!

want to add a few things. https://www.amazon.com/gp/product/B081SFN2FG/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 this cable is great. I noticed much better color accuracy over standard HDMI copper.
 
the guys over at https://www.rtings.com/tv/reviews/lg/cx-oled do good work reviewing tvs. they have some basic settings to improve out of the box quality and should compliment OP's info as these panels don't have much in the way of variance from what I have seen.

Jstandaert
want to add a few things. https://www.amazon.com/gp/product/B081SFN2FG/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1 this cable is great. I noticed much better color accuracy over standard HDMI copper.
 
the guys over at https://www.rtings.com/tv/reviews/lg/cx-oled do good work reviewing tvs. they have some basic settings to improve out of the box quality and should compliment OP's info as these panels don't have much in the way of variance from what I have seen.

Lol when opening the rtings.com link, the text is GIGANTIC on my CX48 for some reason.  It's normal sized on every other website and in windows in general.  Kind of ironic that that that page in particular doesn't scale right on the CX48.

By the way, always double check settings after a firmware update to the TV.  I've found out the hard way that it resets some stuff sometimes.  Spent a long time troubleshooting issues in windows that were a problem stemming from a firmware update resetting the TV/monitor settings.

wow

hmm 🤔

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.
 

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!

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
 
The Ruipro will sometimes allow me to get 4K 60Hz from the TV category, but it's inconsistent. I can also get the 1080p under that category at 120Hz, but any resolution with RGB, full or limited, even at 8-bit Output Color Depth, will result in a blinking screen as if it's trying to change to the higher resolution, then a completely bottom out to 1024x768.
 
I've marched through the last three driver packages from nVidia (466.77, 471.41, 471.96) with DDU in Win10 safe mode like an ant on crack with no change observed.
I've reset the LG CX tv four or five times to initial settings, ticked all the right boxes (PC mode, Instant Gaming Response, Deep Color). Latest firmware (3.23.25). Tried different HDMI ports.
I've run Precision X1 and updated the firmware on the card, even ran a curve overclock (card switch set to OC and is in a WC loop on an EKWB block that never let's it get above 52C on the OC curve test).
 
As near as I can tell, either all these cables are absolute trash, the card HDMI port is faulty, the drivers are crap, or the CX just won't run 4k 120Hz.
I've got the RUIPRO 8K HDMI Fiber Optic Cable 15ft HDMI 2.1 48Gbps 8K@60Hz 4K@120Hz Dynamic HDR/eARC/HDCP 2.2 on the way, but not much hope for it.
 
System Specs:
Gigabyte Z370 Gaming 7
8700K
32GB GSkill 3200MHz RAM
Samsung 970 Pro 1TB NVMe boot drive / 970 Evo 2TB game drive
Win10 Pro 21H1
 
edit: tried to link the cables, forum ain't havin it.
 
Edit #2: Since the last nVidia driver installation (471.68), I've found that certain resolutions can be switched to from the Windows Display Properties. 2560x1600, 3840x2160, and 4096x2160 are all accessible through this route and reflected in NVCP as TV resolutions. All resolutions hit a limit of 60Hz; higher refresh rates are ignored and return to the original resolution.
 
Any attempt to improve Color format or range through NVCP result in a prompt switch right back down to 1024x768. However, I can increase color depth to 12-bit.
 
Also interesting to note, once the resolution is changed in Windows Display Properties, it can be changed in NVCP. If going from a resolution in the PC category and changing resolutions in NVCP, it will drop to 1024x768. PC resolutions in NVCP above 2560x1440 are still inaccessible, presumably for the refresh rate increase to 100/120Hz.
 
This points to a driver interaction on some level, but I can't entirely rule out the cable (as much as I want to). The overall behavior implies a bandwidth issue, and I can't A/B test the cables to prove they have the bandwidth available.

I had an issue with EMI interfering with the video signal at 4K 120Hz (1080P was fine) - the CX would blank out all the time, seemingly at random.

Rerouting my HDMI cable away from the PSU / GPU and using a shorter HDMI cable (6 foot instead of 10+) with EMI chokes fixed it for me.