My sam's don't cover that chassis (but the vert ckt may be the same)...I'm checking my zenith lit.
EDIT: I've got the Zenith issued schematic. Here are the PS and vert sections. C255, C258 and C259a would be my first suspects....55 or 58 caused very weak vert in my set.
BTW: The "service" position of the service switch on the rear of the chassis is designed to collapse the vertical to a single horizontal line (for the procedure of setting the screen/G2 adjustments) and the "normal" position of the service switch is supposed to allow normal/full vertical deflection.
Good luck.