Lights go off after some time, tv stays on

@elvisperika TCL does use cheap backlight strips. This sounds like one of those cases where your backlight gets hot turns off, and then turns back on. Sometimes you can "nurse" it along for a bit longer by changing your brightness and color temperature in the settings menu. The darker you keep the screen teh less power to the backlights.

Anyhow, let's check it out.

Once your display turns dark and you are on a channel where you can hear the sound. Next, use a flashlight and shine the beam at an angle against the screen. See if you can make out shadows or shapes. If you do, then it is your backlight that has failed. If you do not see anything, unplug your set and remove the back cover. Then visually check the boards for any obvious damage like domed or leaking capacitors. Check all the wiring and unplug the wires and plug them back in, make sure they are properly seated. Post some images of all of your boards with your question. Use this guide Adding images to an existing question for that so we can see what you see.

@elvisperika let's say I am 98% sure :-) The backlight gets it power from the power board. The backlight circuit gets turned on by the main board. It is very, very uncommon for the power board to lose the power for the backlight and then to turn it back on. The power board is more of an all or nothing situation. The same for the main board. If the main board tells the power board to turn the backlight off, it usually also turns the video/audio off. That results in a negative flashlight test. Of course, anything is possible and circuits change etc. You can always use a voltmeter and test the voltages to the backlight LED's. Check what values you get when the lights are on and when they are off. The same for the main board. You can always measure the BKL_On part when the lights are on and when they are off. That would show you that your circuitry is still turned on. etc.

I am absolutely good with giving that a try. Just post a couple of pictures of the boards etc. and we can point out where to measure and hopefully find a little information on the voltages. Otherwise we have to refer to common voltages.