HelloWelcomeThanks for using JustAnswerDoes it do this on other inputs like a dvd/bluray/vcr?
Does the blinking look rather like an old cartoon flicker?
How old is the set please ?your country hasn't come up please indicate (where you are)
Its the backlight flickering this is the lamp that illuminates the pixels, it could be flickering because its faulty itself (bad news)or because the invertor that controls it is bad, so the invertor is the most suspect here
I may be able to locate an invertor(s) if you can fit?