Found a Zenith

[hi_volt]

Looks a lot like one of the Zenith sets I acquired in January. Good score! I like the danish modern cabinet.

[Penthode]

I have been doing a bit of work on this set, as time permits, over the last month or so. I stripped the cabinet, restained it in Chesnut Brown and relaquered it with three coats of aerosol laquer.

It was a smoker set so there was tons of gunk to clean off from the interior. I removed the HV cage, removed the HO Transformer and cleaned it fully out. It is now pretty spotless.

I replaced a few cracked coils, the power connector and the curcuit breaker. I fashioned a couple of knobs to replace those missing. Still need the control door.

Fired it up on the weekend and did some trouble shooting. All appears to be in order EXCEPT for the HO Transformer. It appears to breakdown in operation so there is no HV. I called Moyers and await their reply.

[DaveWM]

can you describe the failure mode of the fly a bit more?

[Penthode]

Thanks for the response. Certainly, I shall share my current woe.

Fired up the set and checked basic voltages which appeared okay. I noticed the HO Tube began to red plate after a few minutes and there was no HV. Checked the H Oscillator and it was spot on frequency and amplitude to the HO Tube was correct and the HO Tube bias was about -60volts.

I loosely coupled the scope to the HO Tube plate and saw a good spike. Removing the HV rectifier cap, I could draw only a small arc. I tried disconnecting the various things that might load the transformer such as the convergence assembly, the yoke horizontal coil and the HV would not rise.

I measured the DC voltages on the plate and cathode of the damper and they were the same and there is no boost B plus. Incidently, I removed the regulator cap to ensure it wasn't loading down the HV.

I finally did some resistance measurements and see there is about a 500k ohm resistance from the HV windings to ground. There should be no leakage from this winding to ground unless there has been a breakdown through the transformer frame itself.

Funny as I tried ringing the coil earlier and it seemed okay. It looks like it will breakdown when powered up.

All thoughts are welcome but it looks like the HO Transformer to me.

[ctc17]

Its always easy to measure the screen, if its high the tube is overloaded, if its low its lack of drive.

I would agree the ring test can be pointless unless the primary is shorted. I took apart several rca ones to repair and rewax them, they all had the same failure, the hv winding was arcing from the top of the doughnut to the bottom with a big carbon trace from one end to the other.

Zeniths seem to fail less because they are potted in that hard epoxy.

From what you are saying I would try changing it.

[hi_volt]

That cabinet is looking might fine!!