I got my 55” S405 picture back. My issue was sound & image that could only be seen w/flashlight. I went researching on youtube. I found that most likely issue was LED backlight strips. I don't know deep electronics or how to trace voltage. But I do know system hardware replacements. It is by no means an easy repair for the novice. The replacements totaled $32. I took a chance this was it for the cost. Cheap LED strips made sense to me. I found a great youtube video on the breakdown. My TV was last gen in this model. The LED strips on 1st models were glued in; not easy to get out. Mine had 1 little screw on each strip, then each slid out easily. Kinda makes me think TCL made it easier to repair knowing they were faulty…
I can't believe how many people have this issue. Boo!