I've seen two of these do the same thing.
Monitor comes in and
powers up on the bench with backlights but will only cycle through red/green/blue/white/black and never prompt "Check signal cable" like a known good monitor will. The status LED changes red to green when I give it a video signal so it detects something.
Swapped the TCON - no change.
Ordered a replacement A/D board (Tovis UD120 Rev1.01) and it's visually identical down to the manufacture date (but the VGA port has been deleted) but when installed
as soon as the backlights turn on my bench supply kicks out. Unplugging the LED driver harness from the board stops that but I can still see it cycling colors when I put a flashlight up to the screen. The pinout for the LED harness on the old and new boards are identical.
I put the original board back in and the backlights work again but I still have the cycling colors and I cannot see anything on the new board that would cause the backlights to kill power as soon as the backlights are turned on.
There was a discussion about this on Delphi Forums back in 2019 but it didn't lead anywhere. -
https://forums.delphiforums.com/slottech/messages?msg=18110.1