How to get a full picture on my 1976 RCA XL-100 console?
 

So I just got my hands on this RCA ColorTrak console from '76, and it's in truly remarkable condition cosmetically. The owners were an older couple who used it sparingly so the picture tube seems to be in great shape as well. The set powers on, but the CRT does not produce a full picture. Instead, static comes down a little more than halfway down the screen and stops at a white line. Everything else seems to be working just fine; all of the fine tuning knobs are in working order and even the channel indicator lights are bright and vivid.

I had a General Electric Performance television from the late 70s growing up that used to do something similar, but the white line would almost always bounce down after it warmed up and produce a full screen image.

Does anyone know what the cause could be? I'm thinking its a bad cap since the CRT looks like its in good shape. I don't quite know where to begin, besides to try and clean out the inside of the chassis. Any advice would be much appreciated, as I'd love to keep this beauty alive and well. I will post pictures as soon as I get off work.
Thanks!

Usually vertical deflection issues are indeed capacitor related.

Additional info: the set is a CTC 81, the chassis and inside in general aren’t terribly filthy, just need to dust them off a bit. Pics attached.