Phil
Try the chassis number also. Should be inside on a white tag, sometimes also on the back.
One good trick with "no manual" is the parts designaters ( R###, D### etc).
Most sets come in blocks like IIRC
800 #'s power supply
400 #'s vert.
500#'s horz/hv
100#'s IF
When you find the vert out IC look for matching numbers.
Example Vert IC IC401. All other vert parts will have a 400 series number.
Odds are is a 'lytic or cold joints on the IC. While in there check for cold
joints under the FBT, very common.....
Those were great little sets. We sold Zenith but they only went down to
13" so we sold the Pannys, no regrets.
good luck
73 Zeno
LFOD !