Think it may be a bad solder connection on the board. You can find it if you have a BIG magnifying glass that is how the tech found mine. When it heats up it expands enough to make a bad connection(short).
Two sets of mine had same prob. and that was the cause. One did it when just out of warranty :-((RCA). The other a cousin gave me, she was going to trash it. Both nice 27" flat screens. First was $60.00 in '91 for the RCA the second, Panasonic, was $10.00 last fall at the tech school :-)
You can get a nasty shock if you do not know what you are doing.
William
August 2006