I'm clearing out some old sets (BTW, Sanjar came and got that Maggie) and years ago I shoved this old Zenith with a beat-up cabinet aside into my basement to be basically a "parts set" for some nicer examples I own.

When I put it away, it was in working condition. Now I want to save the chassis and dump the cabinet/CRT, but first I wanted to be sure it still worked. So I fired it up, and no HV. After a few extra seconds, the Horizontal Output starts getting red.

I cannot recall if this is a symptom of a bad HO, (6JS6) or a bad HV rectifier (3A3A) (or both) I think a bad HO always kills the HV rectifier? I'm rusty.

Which tube (or both) would you sub? Is this likely just a tube? Like I said, worked OK when put into storage years ago.

Someone will know much better than me, but could it be dead horizontal oscillator/drive?

The lack of horizontal drive to the HOT would be the first thing I checked.

Check the 6U10 (hor osc) first. Then remove the cap from the HV rect. If you get HV with the top cap off the HV rect, it's shorted.

Jeez, I feel bad you did all that pro diagnostic work! Since I didn't get the quick "Art Margolis" type answer, I just packed the thing back up whole yesterday. I didn't want to put the chassis on the shelf without fixing the problem. So in a way, a bad component saved this set whole till I have to purge again.

However, I was unaware the H. Osc could also be a cause. I'll keep that in the memorybanks.

Easy way. Check the screen voltage on the HOT, if its high its an overload(bad flyback, shorted rectifier, cap, damper). If its low the problem is lack of drive to the HOT.

This one test instantly tells you if the issues is before or after the tube.

Ohh, btw...there is no 20xc36. I beleive there is a 20x1c36 and 1c38. i would look it up and tell you the pin number and voltage of the screen if i knew the chassis.

He said 23XC36, which there is indeed such a chassis. All zenith's of this era had either the 6JS6A, or a 6LB6 HOT, both of which have the same pin number for the screen grid (pin 5). It needs -60/-70 volts of drive to be satisfactory.

Im an idiot, I read that as 20 not 23. (long day, late at night)
Yea I know they all use the same tubes and the Grid is the same negative, Im talking about the screen, pin 3-11. Should be 135v. If its higher, say 180 the drive is there and the tube is overloaded. If its lower, say 50v there is a drive problem.

This is a good test for this set because those pulse regulators are problematic. If a resistor goes bad or the vdr fails that tube will clamp down and cause the HOT to red plate. Looks like on this set you can just pull the 6HS5 out and see if it fixes it.

http://boxcarcabin.com/23xc36.jpg

Carmine, The same circuit was used for years. I two 1967s like that. One of them, the HV went too high, it arc'ed thru the CRT, breaking the neck.

I have a similar problem on a 12B14C52 (same basic tubes and circuit) a damper red-plating, causing HOT to spark insides and its immediate toast. I haven't had time to look into it, but it was suggested the same issue with the 6HS5 (6HV5A) over-conducting due to pin 2 going higher than 260v. R143 or C91 in the grid circuit are prime suspects per some of the gurus here.

R142, a voltage dependent resistor breaks up. Changed hundreds of them when these sets were popular along with the regulator tube. Some sets devoured the regulators and horizontal output tubes. I would check that first!