Fixing 55" TV
The TCL 55S405 is a 55", 4k Roku TV. I found one in the alley behind my house that someone was throwing away. Looking at it, it seemed undamaged and I was confident I could figure out how to fix it.
After plugging it in, the image was present but only when a flashlight was shone across the screen. This let me know that something was wrong with the backlighting of the TV, but it seemed otherwise operational. Following a video by BigDog8882 on YouTube, I disassembled the TV and replaced the backlights with a set of replacement LEDs from Amazon that I purchased for $30.
Multiple back panels need to be carefully removed to access the backlights.
The display and diffusion sheets need to be carefully removed before the LED strips are fully accessible.
I replaced the original LED strips in the TV with the strips from Amazon. It is likely that only one LED is faulty, but I don't have access to the equipment I would need to determine which LED is faulty and carefully replace it. I decided it would be simpler to just replace all of the strips, especially since they were such a reasonable cost.
After replacing the LED strips, the TV powered on properly on the first try.
The backlights are not properly tuned for the display, meaning that when the whole screen is a uniform dark color or uniform light color, you can see the LEDs through the diffusion sheet. This is minorly bothersome, however when watching movies or videos it is not noticeable at all.
I am thrilled that this worked, the overall repair went perfectly and it only took about 5 hours of work.