Look for a non-polar electrolytic around 10 uF or so, 50 to 100 volts.
In the vertical drive to the yoke.

As old as that set is, suspect any of the electrolytic. Borrow an ESR meter
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I would suggest looking for a large lectrolytic, either polarized or
non-polarized, in the connection from the verical output transistor to
the deflection yoke. Odds are at least 10 - 1 that is the problem.
And, please let us know what you do find, it adds to the total
knowledge on this site.