[Arran]

Eliot,

Thanks for heads up. Once I finish my AA5 Zenith 6G001, (just restored a quad electrolytic cap) this is my next project. Can't wait. Never saw a motorized drive before.

Motorized dials were quite common on the higher end sets from about 1937 to 1940 or so. The Zenith system is quite crude compared to an RCA, the RCAs have presets for the various stations, that Zenith just has a spring loaded switch that you press to move the dial, and I believe that you need to flick another to make it go in reverse. If the motor isn't working then it's likely dried out grease, a blown fuse, a bad motor run cap, or a wiring problem.
Regards
Arran