Question Diagnosing backlight issue on a TCL 55s405

Sep 14, 2021
Hey everyone,

I have a TCL 55s405 that just had the backlight stop functioning over the weekend. The unit still powers on, still produces sound when pressing buttons on the remote, and using a flashlight on the screen allows me to see that the menu is being displayed, so I'm confident that it is just the backlight that is the issue.

I have opened it up and tested voltage to the LEDs from the powerboard, and think I have determined that it is an issue with that board, but wanted to make sure before I start dumping money into parts. There are 4 wires connected on the 10 pin connector and the voltage I get on the 4 pins with wires are as follows:

Pin 9- Top wire (black) - .7V
Pin 7- Second wire (red) 0V
Pin 4- Third wire (white) 0V
Pin 2- Bottom wire (red) 0V

Pins 7 & 9 are one circuit and Pins 2 & 4 are another. Considering that I'm getting different results from each of the circuits, and no voltage at all on one of them, I figure something is definitely wrong there. Am I safe assuming that the power board is the issue or are there further tests I should do to confirm that?

Thanks for any help or recommendations you can give me!
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