I have done that. There is no visible evidence of anything amiss. I probably should have been more clear about the screen appearance.

The screen is "black". The backlight works and the touch screen function works as well. So, CCF information is getting to the screen, but the contrast function is missing. Rotating the contrast pot produces no change whatsoever.

I'm wondering if the contrast pot is broken internally. Alternatively, something else in the contrast "chain" is defective. (Wish I had a circuit diagram!!!).