Lost yCbCr option

Hi guys,

I've encountered a really weird problem using HDMI2.0 between my GTX 970 and my Sony XD93 UHD TV.

I had it working just fine, using 4k resolution, 60hz and the yCbCr 420 colour format. My TV accepted this as an "enhanced" 10 bit HDMI input. All good.

However, I then stupidly decided to try changing the colour format to yCbCr 444. My TV stopped recognising the signal completely and displayed nothing. After some research I've come to the conclusion that my TV will not do HDMI2.0 unless the 420 colour format is used.

The crazy problem I now have is that in the Nvidia control panel the option for yCbCr 420 has completely disappeared when I change the resolution of the TV. I can only select from RGB, yCbCr 444 and yCbCr 422. None of these work, I need to get back to the yCbCr 420 option.

I've tried a clean driver reinstall but this has not helped.

Does anyone have any ideas? I'm so annoyed that this was working fine and now I can't return to the previous setup I had... Is there any way that I can use CRU or similar application to force the correct colour format?

Thanks