I highly doubt if a sync separator tube would cause a no horizontal sweep/no HV problem. Does the horizontal output tube 6BQ6 get really hot? If so, there is little or no horizontal drive to it, or also in that case it could also be a shorted flyback. Pull the cap off of the HV rectifier tube (1B3), and see if you can draw an arc with a insulated screwdriver off the lead from the flyback. If the 6BQ6 runs somewhat cool, then maybe there is a problem with the power supply, causing no B+ voltage to the horizontal stage. Also what about the horizontal osc tube, and it's components. Another thought, would be a shorted out "bathtub" HV capacitor under the 1B3/1G3 HV rectifier tube. Is there a separate fuse for the horizontal stage? Do you have the schematic for the set, and if not many times you can find them on the web for free, maybe from the early television website. http://www.earlytelevision.org/tv_sc...s_u-v-w-z.html
Also I'm sure you will have to re cap the set, which is fairly easy if your good at soldering, just very time taking.
Good luck, portholes are definitely a unique type of TV.

I think you should continue on with your restoration of that Porthole TV.
Restored and working Portholes are a treasure - they are so unique.

If your Flyback is indeed bad, perhaps someone here has a cross reference of your
S-17233 Zenith part number to a Stancore, Merit, Chicago, etc. When I restored
my 1950 Zenith porthole someone gave me a reference to a generic Flyback that
I remounted on top of the Chassis rather than below.

Thanks for your input Walt. What I no longer have (Because it went when I sold my TV repair shop business back in 1995) is a HV probe. I'll have to get one of those. All of the horizontal sweep related tubes, horizontal output tubes and the 1B3 tube check excellent. The only bad tube was the 6BN6. What I need to do at this stage is to pull the chassis out of the cabinet but that will have to wait for a while. Gary

Thanks for your advice CW. I do indeed plan to continue with the restoration. I plan to pull the chassis out from the cabinet sometime in the future when I have bench space and time to work on it. Gary

don't rule out the fly until the set is recapped and resistors checked but if you had a fly tester it would tell you , and a hv probe doesn't hurt