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

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? 

 
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.
 

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.

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.
 

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.
 

I think you have some wires crossed. I do not use passthrough at all. The AVR takes in the DP to HDMI audio signal as a dummy display from my 3090 FTW3. I use the 3090 FTW3's only HDMI 2.1 output to go direct to the TV for video display only (the TV is also not used to passthrough to the AVR, as I've read that there is serious audio lag with surround/atmos).
 
This completely bypasses any limitations my 4K 60Hz AVR has for PC gaming on my LG CX, but I can still enjoy surround sound (and Atmos again when Dolby fixes what they broke with the last Dolby Access app update).

arestavo
 
I think you have some wires crossed. I do not use passthrough at all. The AVR takes in the DP to HDMI audio signal as a dummy display from my 3090 FTW3. I use the 3090 FTW3's only HDMI 2.1 output to go direct to the TV for video display only (the TV is also not used to passthrough to the AVR, as I've read that there is serious audio lag with surround/atmos).
 
This completely bypasses any limitations my 4K 60Hz AVR has for PC gaming on my LG CX, but I can still enjoy surround sound (and Atmos again when Dolby fixes what they broke with the last Dolby Access app update).

Ahh okay, so I think you have a fairly similar setup then -- except I am using audio passthrough on my TV to my DAC-AMP via Toslink. I haven't really noticed any audio lag myself. It could be a worth a quick test to see if you still have display issues. What I like about the way I've got it setup, I can use TV speakers in lieu of PC speakers, and headphones whenever I want -- or both at the same time. I still feel the adapter is likely a source of problems.

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.

For my #1 it really seems like all I have to do is get the display to switch modes (HDR/SDR) and the brightness levels return to normal. It doesn't even seem to matter what I do to force it to occur so as soon as I launch a full screen game it's actually fine, and when I ultimately return to the desktop that's fine too. Certainly not perfect, but it's just a minor inconvenience in my book now that I know what solves it.
 
For my #2 I can't really seem to find a reliable fix, other than just to never shutdown the PC which isn't really a fix so much as a crude workaround. It seems to have something to do with the PC being shut off and that initial handshake process with the display, or something of that nature. I've tried powering the PC on first, then the CX and vice versa with no real change in behavior that I can observe. From my perspective it seems to just randomly work again, never taking more than a couple minutes. Then as soon as it works....as long as I don't shut it down...it's fine until I shutdown. Strange stuff.

Just confirming that Zeskit 8K Ultra HD High Speed 48Gpbs HDMI Cable 3m fixed all my issues. Now on latest LG C9 firmware, I can now run 4k 120 HDR 10 bit and G-Sync with no weird issues. The cable is good quality and near enough twice the thickness of the Amazon basics I had before.

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? 

#1 I believe is a windows issue. I first noticed it with my PG27UQ 4K 144 hz 1000 nit gsync ultimate monitor via displayport 2 years ago and it still happens regularly. Now I'm noticing it over hdmi on my C9. Just one of the many Windows 10 HDR quirks. 

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?