There is a good possibility the picture tube is bad, If it is a zenith from 1990 to 1996 your chances are 98% The tubes they used had a high failure rate. There is the possibility that the solder connections from the crt socket to the pc board have become cracked from thermal expansion. Check that, It is real easy, Once the back is off the set, The crt board will be facing you. Take a strong light and check the solder connections that are in a circle, These are the socket to board ones. If there any dark circles around any of the pins, Or if when you gently tap the board with a plastic stick while the set is running, And the problem goes away, Then you have it!