The closest US model for your set is SM1971P
You may find a factory manual on E-Bay.
If not look for a Sams Photofact manual. The manual number
is 2010-2 for Sams. You can by from Sams but $22 US and you
get a poor PDF.
Some used Sams dealer.
http://www.theschematicman.com/
There was also a factory training manual. IIRC they called
it the XXX chassis. Zenith stopped using real chassis numbers
about 1979.
Your 13" looks good. one thing to check is a cap on the 9-160.
IIRC its 10mf 315V & on the right rear near the FBT. Very
common & causes many symptoms. Another thig is on the 9-155
look for open resistor from G2 control.
73 Zeno