phantomapollyon
Update to confirm for those that may be interested: I'm using the 3m cable from Zeskit mentioned earlier in the thread with no issues at all up to 120Hz on my LG CX65 & 3090 FTW Ultra. (latest hotfix drivers, manually set the profile/resolution/refresh, latest XOC BIOS on the 3090)
 
https://www.amazon.com/gp..._s00?ie=UTF8&psc=1

1. Sometimes when I leave the computer idle for a long while with the TV turned off, when I turn the TV on all the settings look correct/identical yet the TV's HDR brightness levels are noticeably low (estimate 20-30% OLED light) and the only thing that seems to solve it is a full PC reboot. After the reboot everything works completely fine for an undetermined amount of time until it happens again.
2. Twice now over the past few weeks I've also turned on the PC and there's some bizarre delay before any video will output, anywhere between 30s-120s in my experience. When it does finally display the system is just sitting at the desktop.

PhantomApollyon
 
 
UPDATE:  I was able to get the Monoprice 6ft cable connected, reconfiguring the room a bit for the sake of testing, and my #2 issue happened right away. Given that cable seems to be working for almost everybody so far, I think it's fair to say this likely is not a cable-specific issue.
 

morness

arestavo
 
So with my setup (DP to HDMI adapter for sound to my AVR, HDMI direct to LG CX) the CX sometimes has no video input if I turn on the AVR first, and I'd be forced to unplug the HDMI to TV or power cycle things.

HDMI has a whole lot of internal handshaking going on. HDMI 2.1 is fairly new and well I don't think DP to HDMI is going to be reliable. Why are you using DP (pre-30x RTX Ampere card)? Also depending on your AVR, it might not support good enough passthrough. If things are indeed out of date, you can connect those directly to the LG, and use a TOSLINK optical out to feed audio back to your receiver. The more daisy chained your HDMI setup is, the worse the handshaking problems get. It has always been bad since HDMI was born. 

PC -> LG via HDMI -> AVR via optical
 
Granted depending on how many consoles/devices you have routing through your AVR the harder it is to flow through your TV -- which is ideal for a simple setup only or bridging the gap until you can upgrade your AVR. I recommend getting rid of your adapter entirely.
 

arestavo

PhantomApollyon
 
 
UPDATE:  I was able to get the Monoprice 6ft cable connected, reconfiguring the room a bit for the sake of testing, and my #2 issue happened right away. Given that cable seems to be working for almost everybody so far, I think it's fair to say this likely is not a cable-specific issue.
 

So with my setup (DP to HDMI adapter for sound to my AVR, HDMI direct to LG CX) the CX sometimes has no video input if I turn on the AVR first, and I'd be forced to unplug the HDMI to TV or power cycle things.
 
So if I turn on the TV first, wait a second for the picture and HDR thing to pop up, and then I turn on the AVR I find that it works. I get a screen flicker which I assume is the windows desktop extension happening, and all good.
 
This hasn't failed me yet, and may be applicable to your #2 problem. As to #1, the only time I see a difference in brightness is if I turn off Gsync and the TV reverts to different settings.

PhantomApollyon

phantomapollyon
Update to confirm for those that may be interested: I'm using the 3m cable from Zeskit mentioned earlier in the thread with no issues at all up to 120Hz on my LG CX65 & 3090 FTW Ultra. (latest hotfix drivers, manually set the profile/resolution/refresh, latest XOC BIOS on the 3090)

https://www.amazon.com/gp..._s00?ie=UTF8&psc=1

Update: I am now experiencing some small quirks that I'm curious if anyone else has noticed/solved. These may be down to the HDMI cable but I need at least an 8ft cable based on where my PC is in relation to the TV so it is what it is, I can't test a 6ft cable. I do plan to try the Monoprice 8ft cable whenever that makes it back into stock on their site, so if/when that happens I'll definitely follow up.
 
Both small issues I've noticed:

1. Sometimes when I leave the computer idle for a long while with the TV turned off, when I turn the TV on all the settings look correct/identical yet the TV's HDR brightness levels are noticeably low (estimate 20-30% OLED light) and the only thing that seems to solve it is a full PC reboot. After the reboot everything works completely fine for an undetermined amount of time until it happens again.
2. Twice now over the past few weeks I've also turned on the PC and there's some bizarre delay before any video will output, anywhere between 30s-120s in my experience. When it does finally display the system is just sitting at the desktop.

 
Anyone experienced these or have any thoughts beyond just switching out the cable, which I fully intend to do when it's available? 

PhantomApollyon
Thank you to everyone for the feedback so far, I tend to agree that my #1 is/was largely just a Windows HDR quirk as suggested and am largely writing that off for now. (though I NEVER experienced this with my 2080ti FTW3 Ultra)
 
My main outstanding concern now is an issue with getting no video output at all from the PC from a cold boot until after some undetermined amount of time, EXCEPT the initial BIOS splash screen. I want to front load this with the fact that I NEVER experienced this with my 2080ti FTW3 Ultra and beyond the GPU/drivers, nothing else has changeg with the system.
 
Generally the delay in video output will be anywhere between 30s-120s, with seemingly no real rhyme or reason as to why it starts working. When it does start working, I'll be at the Windows 10 desktop. What's interesting to me is that it always shows the BIOS splash screen just fine (not HDR), and once it starts to boot into Windows, the signal cuts out and the TV shows no signal though it does recognize that something is plugged into the HDMI port if you look at the input window. While doing some testing this morning I actually had a white VGA error light on the board show up after waiting ~2minutes for video to display, and when I was walking over to look at the LED the screen lit up without me touching anything at all. I did a power cycle and the VGA light was gone and things are working normally again. It's almost like something's odd with the HDMI handshake as it attempts to boot into Windows, which triggers HDR. 
 
Any thoughts on this one?

• AudioQuest Pearl 5' 8K-10K 48Gbps HDMI Cable --- Confirmed no problem, 4k @ 120, 10bit, G-sync, 4:4:4

Qaedyn

• AudioQuest Pearl 5' 8K-10K 48Gbps HDMI Cable --- Confirmed no problem, 4k @ 120, 10bit, G-sync, 4:4:4

So I picked up my CX 48 at Best Buy yesterday and got an AudioQuest Pearl 5' 8K-10K 48Gbps HDMI Cable have had no issues with my 3090 ftw3. First thing I did was upgrade my firmware to 3.11.25. Any of the AudioQuest 8d-10k listed cables at Best Buy should be fine but anything over Pearl gets expensive quick and you only gain better auto quality apparently.
 
Edit: Woops restrictions on new members and links...sigh. Tried to post links to the cables. Just search for the Pearl or Ocean (apparently same quality as Pearl but BestBuy exclusive) 8k-10k HDMI Cables at BestBuy. Also AudioQuest has their own site as well if you want to see more info on the cables.

arestavo

PhantomApollyon
Update: I tried the Monoprice 6ft cable with no change in behavior at all - still having the same issue

I just read that someone else fixed a black screen problem by enabling HAGS. I personally don't have it enabled and everything works, but maybe it will work for you? https://www.pcquest.com/w.dows-10-may-update-hags/

MrEWhite
I'm using this 25ft fiber cable as my PC is quite a length away from my LG CX 55 @ 120 Hz with HDR on and no full RGB and it works fine with my RTX 3090

MrEWhite

aldur80

MrEWhite
I'm using this 25ft fiber cable as my PC is quite a length away from my LG CX 55 @ 120 Hz with HDR on and no full RGB and it works fine with my RTX 3090

Dang, I need at least 30 feet, although I'm tempted to pick up a 50 foot one as it's still way cheaper than the 30 foot monoprice cable I bought.

I meant "full RGB" in that post, dunno why I put "no" there

MrEWhite

aldur80

MrEWhite

aldur80

MrEWhite
I'm using this 25ft fiber cable as my PC is quite a length away from my LG CX 55 @ 120 Hz with HDR on and no full RGB and it works fine with my RTX 3090

Dang, I need at least 30 feet, although I'm tempted to pick up a 50 foot one as it's still way cheaper than the 30 foot monoprice cable I bought.

I meant "full RGB" in that post, dunno why I put "no" there

Do you have to disable "Instance Game Response Mode" and enable all the time to get gsync to work? I have to do this every time before I play a game or the TV flickers and gsync stops working.

Nope, works fine for me.

MrEWhite

aldur80

MrEWhite

aldur80

MrEWhite

aldur80

MrEWhite
I'm using this 25ft fiber cable as my PC is quite a length away from my LG CX 55 @ 120 Hz with HDR on and no full RGB and it works fine with my RTX 3090

Dang, I need at least 30 feet, although I'm tempted to pick up a 50 foot one as it's still way cheaper than the 30 foot monoprice cable I bought.

I meant "full RGB" in that post, dunno why I put "no" there

Do you have to disable "Instance Game Response Mode" and enable all the time to get gsync to work? I have to do this every time before I play a game or the TV flickers and gsync stops working.

Nope, works fine for me.

Which version of LG firmware are you on?

03.11.26. I got it from LG's website before they swapped it with 03.11.25. Works fine with VRR on my Series X too.

Naur1 Anyone try using custom resolution but only getting 8bit and not 10 bit as an option?  Native 4k resolution 10 bit is fine but if I do 3840x1850 it only flickers and goes back to 8bit