[drh4683]

Does it have the concentric tuner? After channel 13, a white window should appear and then you adjust the outter knob thats used for fine tuning VHF as the UHF tuner. A smaller diameter drum is inside the VHF indicator drum that has the UHF channel numbers on it. They can be hard to turn though, Ive seen these tuners with stripped teeth on the UHF dial drum when someone forces the tuner when its stuck.
No color sync with AFC on? How is color sync if you offtune the set with AFC off? AFC module may be out of alignment, which is an easy to correct. however, First thing is to check all those tubes and be sure you use a tester that can test for grid emission. So many people use testers that don't test grid emission and a bad tube slips by every time causing problems. The 6JU8 color AFC is a common suspect for color sync issues though.
Poor CRT may=poor focus, however its common to find a zenith with focus that won't come in sharp enough. A brightener on a CRT is basically a death sentance to the tube (kind of like "instant on"). Open up the HV cage and replace the 212-85 selenium focus rectifier. Replaceing that will bring the focus back and the control won't be at the end of its range. Its soldered in, its brown in color about 2.5" long on the right side of the flyback board. The correct replacement is an NTE-118, you might have to shop around the internet to find one as I dont think NTE makes them anymore. Moyer of course would be the best bet to find one.