Vizio P65-C1 extreme brightness issue

This morning I powered on my P65-C1 and the screen was incredibly bright. By bright I mean almost white. We had made no changes to any settings. I tried adjusting brightness and backlight and no change. It’s just plain ‘white’. I’m used to TVs eventually dimming, not the reverse.

I’ve done some research but can’t find any references to this specific issue. I’m not adverse to trying some repairs rather than having to replace it, it’s only a few years old! TVs sure are what they used to be!

Can anyone suggest next steps? I’ve tried factory resets, everything it just stays white. Could this need a motherboard replacement?