I have sound and backlighting but no picture.

@davidp87045 this sounds like either a mainboard issue or the driver boards. There is always a minute chance that this is possibly firmware or video source related. So, start off with this. Disconnect the TV from the power cord. Disconnect all external devices (cable box, Sat box, game console etc.)from the computer. Now push and hold the power button depressed for about 30sec-1min. Next reapply the AC power adapter and see if your TV shows the TCL splash screen. If so connect one video input source and see if it works as it should.

If not then your next move would be to remove the back cover and do a visual check on all of the boards. Check for components that appear damaged, burned charred etc. or even missing. Check all of the ribbon cables for any rips or tears and corrosion. Remove them, inspect then reinstall. Check the LCD driver boards (long skinny boards that connect directly to the LCD panel ) for any abnormalities. Post some good pictures of your boarsd with your Question. That way we can see what you see. Adding images to an existing question

There are many suspects that could cause this but my money is one either the main board or the driver boards. For the driver boards, you could always try a Tape-Off and see if you get any sign of life from the display.