Winking Zenith Porthole
 

Chassis 22H20 (H2227R). Works fine EXCEPT video flashes on and
off at about 1 second intervals. Tubes check out fine, have full screen with some retrace so I figure a cap is charging up and dumping its voltage; an electrolytic, perhaps?
Outside of trying to meter these voltage changes with the set
on, any suggestions as to where to start?

Thanks!

It's breathing!
 

Michael,

I had a similar problem with my 1947 Admiral 30A13 chassis. It went away when I stopped trying to use rabbit ears in a fringe area and put a good strong signal from a VCR into the set. Your problem may be that the AGC circuit has an open time constant electrolytic capacitor and is motorboating due to slow time constant positive feedback. Without looking at a schematic the AGC is generally a common bias line that supplies the grids of at least the IF tubes, and sometimes the RF amp in te tuner as well from an AGC detector like a 6AL5. The grid resistors will not go to chassis ground in this case, but to a bus bypassed at each tube feed by a small disc capacitor.

Rob