OK not the vert.
Looks like its loss of video. Most likely a problem on the 9-88
board.
I would clean the tuner before it drove me nuts. Also
the service switch on the chassis ( not the one on the 9-86).
Check the 4 lead cap thats strapped to the H out heat sink.
If its orange you are OK. If its white get a new one before
you work on it. Part ## is 800-860 IIRC. Often on e-bay.
73 Zeno
LFOD !