So 3 months later I finally got around to pulling the screen of the TCL 43 inch with the 2 black spots. Turns out was my fault lol. I have never touched these small cheap brittle plastic models before and when I had the bezel off and the screen lifted out to check the led strip ... two tiny plastic square clips from the bezel had fallen in behind the screen onto the diffuser. There was enough of a static charge in the plastic that they just hung on to the plastic diffuser sheeting. I took them out and now is perfect picture and thank god was not dead pixels in the panel. Gee my dumb arse is learning...