Hi Mate my LG 65UF680T tv started doing exactly that just last night and I've been trying everywhere for answers.
I'd be very interested if you get some answers cheers.
We are in Shepparton Victoria , ours surprisingly worked last night no idea why or how but i expect it will fail again .
Not sure but isn't there a signal strength check in settings which you still should be able to see .
My thoughts as of now is that its probably the main board , we know it's not the screen and probably not the power board .
