well it will prob be something simple.
a few things I always do, pull the horz and vert out, do a slow power up while monitoring the AC line currrent (metered variac) and the B+ and temp of the filter caps.
I theory is this will give a cap time to reform (if its going to reform) and will also quickly let you know if there are any shorts in the B+.
Pulling the horz and vert is just done as a preventive measure in case the low voltage prevents osc and bias issues on the tube.
Typically I will let this process go on for several hours starting at about 10vac and working up to about 80vac, as long as the B+ seems ok and nothing starts to heat up.
My guess on yours is a shorted filter cap followed by a smoked resistor in the filter network.
I did have a zenith with a shorted disk cap but that was an easy fix and the only thing that was wrong with it. I did not even pull the chassis, just replaced it with the service saver chassis cover removed.
Good luck with your zenith
