Oh many many things my friend. You could have simple bad connections on the printed circuit board, perhaps a vertical sweep falure. Maybe a problem in the convergence circuit. It is impossible to tell on most sets when the problem is so generic like you describe. I wish it was that easy to diagnose a TV set like that. You will first off need to have TV circuit trouble shooting capabilities and know how to follow circuit flow and to use a schematic diagram to see what is working in the set and what is not working. If you have no TV repair experience, play it safe and call out a trained service tech to assist you with your repair. Good Luck
Oh many many things my friend. You could have simple bad connections on the printed circuit board, perhaps a vertical sweep falure. Maybe a problem in the convergence circuit. It is impossible to tell on most sets when the problem is so generic like you describe. I wish it was that easy to diagnose a TV set like that. You will first off need to have TV circuit trouble shooting capabilities and know how to follow circuit flow and to use a schematic diagram to see what is working in the set and what is not working. If you have no TV repair experience, play it safe and call out a trained service tech to assist you with your repair. Good Luck