The Sams website says the manual for Zenith chassis 19L27 is 232-11:
https://samswebsite.com/en/photofact...index/id/14447
If nobody here happens to have it, you can order direct from Sams or watch for a copy on eBay.
As others mentioned, replacing the electrolytic & paper caps will likely fix the picture problem and also make it reliable/safe to play regularly. If you haven't replaced caps before, this article provides basic info about that:
http://antiqueradio.org/recap.htm
This article describes some other basic restoration procedures:
http://antiqueradio.org/FirstStepsInRestoration.htm
The following page lists a bunch of TV restoration articles. None of those sets is exactly like yours, but if you skim one or two articles, you'll get an idea what's usually needed to get one of these old sets working well:
http://antiqueradio.org/televisions.htm
Regards,
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html