the first time i encountered this symptom , it was on a 9" tv/vcr combo.
once i found the culprit ( took awhile) , it made the next encounters a snap.
with VERY good lighting , and magnification, inspect the vert yoke windings for a wire break.
vert windings have 2 identical coils wired in parallel.
when one side is open , what you see is what u get.
u may be able to solder the wire - or yoke replacement will be required
good luck
qrz