Chosen Solution
I saved this M75-C1 from someone’s trash. For the first three nights the TV worked great even though the guy told me there were issues. The next night the TV made a loud white noise/screech sound from the speaker on the left if you are facing the TV’s screen. The sound lasted a few seconds and would happen every few minutes. After that the TV turned itself off. I turned it back on and a few minutes later it turned itself off. After leaving it off for several days then trying it. It worked great for about 30min then it did the same thing. Which leads me to think it is a overheating problem.
@linderben sounds like your TV is having issues with the main board. Remove the back cover and post some good images of the boards with your QUESTION. That way we can see what you see. Use some freeze spray on the main board when it has one of it’s screeching episode and cool the various areas on the main board down. See if that helps you to locate the specific area that gives you the trouble. Since there are no schematics available it is most likely an issue of replacing the board but let’s see what we can find out. Adding images to an existing question
