1966 Zenith 20X1C36 failed vertical output transformer

[Dave Drez]

Thanks for all of your input!

I spent most of today troubleshooting the vertical linearity issue. I did not find any "smoking gun" components that were bad, although I am ordering some caps and will replace as these are original. I do not have a tester that can test for leaky caps... (maybe I should). I'm not sure if ESR testers help with old TVs... Everything I test, the Blue ESR meter says it's OK.

The linearity control does effect the bias at the cathode, as it should. The only question is the grid. I see a proper waveform with the correct voltage at the grid. The Sams says there should be -5 volts DC at the grid and I don't have anything.

I reached an alright compromise today by using the relative interactivity of all the controls. I compressed the height via the "ineffective" vert linear control and expanded the vertical size to get near the correct height, then adjusted the vertical centering. Back and forth a few rounds and to my surprise, the linearity had changed for the better. A couple of the controls are at their maximum travel though. The image has a kind of "bubble" look to it but when I adjust the pincushion transformer, it doesn't have the change I expected. I'd call it "tilt" from my CRT projector days (maybe this is my trouble?). Adjusting the convergence helped with the improved appearance of the geometry as well.

So anyway, fooling around with those things improved the geometry to a point it's watchable but I am going to keep at it. Feel free to tell me it is as good as it gets!

Thanks,

Dave

[Electronic M]

Most caps leak and act strange at ~50V+ and most ESR testers can't come close to that.

Without a test pattern picture it's hard to judge picture quality...also be wary of modern signal sources some distort the picture and if you adjust a working set to make a distorted signal look better that isn't the best solution.

[JohnCT]

Originally Posted by Dave Drez

I reached an alright compromise today by using the relative interactivity of all the controls.

LOL, they do indeed affect each other! Raising and lowering the height control constantly affects the lin, so any adjustments of height and lin need to be back and forth along with the centering. I always hated the vert adjustment dance and sometimes - just when you had it real close -you'd find that the vertical sync was iffy with the best geometry!

I'll never forget the first time I adjusted the vertical height on a SS TV back in the early 70s. I couldn't believe the height control adjusted only the vertical scan height, and that there was no linearity adjustment whatsoever.

John

[Dave Drez]

Thanks for those thoughts! I have a great piece of test equipment by Sencore. It is a VA48 video analyzer built in the late 1970's / early 1980's. Its manual makes it sound like a TV repair shop in a box. It does a ton of things: it will generate drive signals for SS or tube circuits, does ringing tests for flybacks and yokes, RF or IF drive and complete signal generator. It can be used to align the entire circuitry chain. I have just scratched the surface with this device. It was made in the era between full SS and older tube sets.

So I've been using this to generate crosshatch. dots, color bars, ect. as I get a feel for this device and the Zenith. I have reached the "as good as it gets" point with the Zenith geometry. As I mentioned, two of the controls are at their maximum and tonight the vert centering pot disintegrated while turning. I guess I found the life expectancy of 55 year old plastic...

I appreciate your experience of adjusting these settings, John. Everything you said is exactly what I have experienced. Everything is interactive! (good or bad) There may be some resistor values that have changed which lead to the extreme control adjustments and I'll pursue that as well.

Has anyone ever gotten excellent geometry on a TV set from 1966? (NOS CRT installed)

Thanks!

Dave

[Dave Drez]

One last comment on the Vertical sweep issues that I have been having with a 1966 Zenith... At the time I posted my comments about the "non-working" nature of the vertical linearity control, I didn't have a set of vertical oscillator and vertical output tubes
to swap. Since then, I ordered a pair and they arrived. I have found that this "newer" vertical output tube has made a tremendous improvement to the functionality of the vertical linearity and all of the adjustments. The geometry is now very good. The "older" tube was a 6HE5 and is now a fully compatible 6JB5. I changed the vertical oscillator tube - a 6BA11 and it didn't matter so much. I kept the 6JB5 in and the Zenith is much improved!

Dave

[JohnCT]

Originally Posted by Dave Drez

I have found that this "newer" vertical output tube has made a tremendous improvement to the functionality of the vertical linearity and all of the adjustments. The geometry is now very good.

Glad you found it. I would have commented that while geometry adjustments were always a song and dance number on any vacuum tube TV, certain TVs of the era were far less finicky. Zeniths were among those that were fairly easy to setup, and under no circumstances should any of the controls in a Zenith be at their limit.

The only quirky thing with Zenith was the audio. I don't know the reason (patent avoidance?), but Zeniths often would buzz in the audio, and indeed had a "buzz" control (potentiometer) on the back apron. Other than that, any Zenith should have excellent geometry and excellent vert and horiz lock.

John