This is kind of off-topic for the website but I thought this information would be usefule. Last week I bought an LED TV from Goodwill and when I got it home it had a black screen–apparently no power. Upon further investigation I found it was not quite a black screen. By shining a flashlight at a shallow angle to the screen i saw there was an faint image on the screen. If I had an input hooked up I would have discovered that there was sound, too. After consulting the interweb, I found out the likely cause was failure of the backlight LED strips. The display panel is illuminated from behind by these LED strips. These strips are prone to failure in many TV/s. It may only be one or two LEDs that have failed, causing all of them not to illuminate. Another symptom of this failure is a brief flash of light on screen when the TV is first turned on. Shopjimmy.com and other suppliers have replacement LED strips available. In my case, the TV has 12 LED strips. I bought the whole set for $40. The reason for failure is the backlight being driven full blast. The recommendations are to turn down the backlight level. You can test the strips to see what LEDs are not working and just replace those, but a wiser course of action is to go ahead and replace them all, as others may be due to fail. There is a circuit board strip that the lights plug into that could be bad as well but in most cases it will be the LEDs.
I found a YouTube video that showed how to replace the LED strips on my model TV: https://www.youtube.com/watch?v=qGk6Nx82SCA
Disassembly was straightforward, taking particular care of the display panel. Once you get down to it, these are the backlight LEDs on the reflector panel.
The strips are attached with two-sided tape; I removed them with a putty knife. These are the replacement strips. They are numbered.
After re-assembling everything, the TV still did not work. However, the screen was not totally black; it seemed to have a faint even illumination. I took this to mean that the backlight LEDs were now working, but, after shining a flashlight, there was no longer any faint image on the screen. This meant the display panel was not working. Taking the back panel off again, I found that I had not properly seated the ribbon cables from the display panel to their connectors. I plugged those ribbon back in and, Presto! The TV worked.
Now, I do not claim that this repair will work every time, but if someone has a TV with this issue, the repair may be worth pursuing. And in the meantime, it is suggested to turn down the backlight on your TV to extend it’s longevity.