Wow, that picture is really shaping up. A bad selenium rectifier on the convergence board would not be unheard of. On my first CTC-11, when I unsoldered the legs on the selenium unit, it fell completely to pieces.
Before it was replaced, simply touching the old rectifier, or the board nearby, made the picture go nuts.
I installed new fast-response diodes that someone sent me. I don't have the type number at my fingertips. Perhaps it is buried in a past thread.
No guarantee that this will cure your problem, but the parts cost almost nothing, and selenium rectifiers are so sketchy that I routinely replace them in radio restorations, just like electrolytic capacitors.
Phil Nelson