It seems that ,might have a problem from the tuner to the video selector section of your TV.
If your TV have a video out, then try to connect it to another TV " video in " input and monitor
if the symptoms still arise. If the video is the same on another TV , the video selector is OK
your problem lies after the video selector to the video IF circuits to the tuner.
If your TV have a video out, then try to connect it to another TV " video in " input and monitor
if the symptoms still arise. If the video is the same on another TV , the video selector is OK
your problem lies after the video selector to the video IF circuits to the tuner.