Ever since updating to firmware 1402 I have been unable to get any picture from my RTX 3090. I pull out and insert the HDMI cable to get the TV to detect the PC and that works to get image but input signal plus is disabled that way. Turning input signal on results in no input screen. Using any other than HDMI port 4 works fine with input signal plus but these don't have the benefits of HDMI 2.1.
I have a CX too and the RTX 3090 works fine with ultra HD deep colors at 4K 120 Hz 10 bit HDR.
It worked on the previous firmware and I hope there will be no unpleasant surprises with HDMI 2.1 and Xbox Series X and PS5 next month.
Well, it worked on an ealrier TV firmware so the new one broke something.
Also tried again with 457.09 drivers that came out a few days ago, still no screen in windows when you turn on input signal plus.
Like @userQ1zu5lCx7x said, you get the boot screen when starting up but windows gives nothing with input signal plus.
<sigh>. Same problem - I just received my RTX 3090 and was so stoked to finally run my PC at 8K. But on plugging it in, the Q950TS automatically goes to 4K@60Hz mode, with Input Signal Plus disabled. If I try to enable it in Settings on HDMI 4, I just get a blank screen. I've managed to get limited success by enabling game mode on the TV (which auto enables input signal plus). But this results in a very washed out image on screen, still in 4K60Hz but no option to change the resolution to 8K. I have a Monoprice 8K HDMI 2.1 cable, which worked fine up till now, but I've only just started testing the high bandwidth requirements of 8K with the RTX 3090. I have a HDMI 2.1 certified cable on order so that I can rule out cable issues, but as you mentioned yours worked prior to the 1402 firmware update, I expect the cable is not the culprit. What a mess, so many HDMI 2.1 compatible devices came out before any input sources were available and now everyone is fighting fires.
Firmware 1403.1 is out on the Samsung website. Does that fix any of these issues? I can't test it myself as I can't install FW from the US region on my Australian Q950TS and it is not yet available via a TV update.
Has anyone found a fix for this no signal issue on an RTX 30 series? I've been using HDMI 2 and getting 4K@120hz but only at 4:2:0, 8 bit, and no HDR. It feels bad not being able to take full advantage of this TV or my graphics card.