Sounds like the timebase has gone. This controls the scanning of the gun (at the back of the tube) that draws the picture on screen. Should be fairly easy repair, but not something you will be able to do yourself.
Mister T2
Mister T2
June 2004
I can answer this question...
My goodman TV only has a picture in the middle of screen?
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Try fixfault.com to fix televisions.