Is tv repair worth it?
Your problem appears to be in the Vertical Deflection circuit. The Vertical Amplifier I.C. may have a thermal problem. One way to prove this is to spray Zero Mist or Component Freeze on this I.C. at the time it is failing and see if it corrects the problem. It will take some soldering and de-soldering skills to remove and replace this component if you can get one. Yes, it probably would cost you between $200 to $350 to repair, at least here in California.