@ThunderousOne, I do believe these cheap TVs have a backlight issue, but three of them doing the same thing sounds like bad luck or something else is going on that may or may not be software related. Recently, I set up a "Westinghouse" TV (poor George is probably turning over in his grave knowing his name is attached to such a cheap TV) for my niece and I noticed that it defaults to the brightest possible setting. I turned it down to "Normal". I wonder if they all come that way and is part of the reason we see so many failures here. Since you have 3 TVs, it might be interesting to know if setting the brightness to different levels affects the amount of time it takes for the screen to go black.
If it is a backlight issue, you should be able to see the picture if you shine a bright light on the TV.
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