look for a cap that goes from the vert out tube plate to the plate of the video out tube. there is a RC circuit in there that prob is used to aid in vertical blanking. See if its one of those paper cap in ceramic tube types. IIRC zenith used a couple of those 1kv ceramic tube caps, that may be one of them.

I cant say for sure if it would improve the vert blanking but again its the kind you cant really test a rated voltage, and it prob takes a beating from the vert spike.

I think most of the time its more CRT related than circuit related, I even looked into better vert blanking patents posted to improve blanking by sending a pulse to the screens of the CRT. If there were patents for it and circuits designed for it I presume it may have been an issue back in the day, at least for early color sets. On my sets with really good CRT's its never an issue.

here is me looking into vert blanking issue (RCA not a Zenith though)
https://www.youtube.com/watch?v=39DlVjo9hSY

I dont have a manual so not sure. It will be a small tube &
dual function. Probably a 6GH8 or 6KT8 If you have a Sams look along under the video amp tubes thats where they usually put it. It may
use diodes instead. What it does is turn off the video during retrace.
If its not turned off you get lines & often strange symptoms.
Whatever you are using may also be adding to the problem.
DVD's VCR's, Digital CATV were not designed for the old sets.
By the mid 70's almost all roundies were gone in our area.

https://en.wikipedia.org/wiki/Horizo...nking_interval

There is more to know than in audio but its a good start, more
than most have !

73 Zeno

I notice most these tubes have a A,B or C at the end of the part number do these make a difference?

I know in audio Amps a 12ax7A is a little better than a 12ax7 in noise.

The 3at2 among others come in A,B or C at the end.

generally speaking it does not really make any diff. the shunt tubes (6BK4) have more lead in the later letters to help with Xrays. Sometimes there are different internal connections on tubes but that is very rare. I would think any will be ok.

If you don't have the tubes, hold off on buying them, the horz out are very expensive, and may not be needed.

I would recommend messing with the horz hold adj a bit to see if you can clear that fold over on the left, and maybe improve the horz lineairity.

It has an external stop, see if it stays locked within the range of adj with the lock in place. If it does and you can improve it, then you may want to remove the lock and try going a bit more to see if you can further improve and still stay locked on. just flip the channel back and forth and make sure you get a good solid lock after adjusting it.

Ok I'll be looking in to everything you guys advised me on. I need to go through my stash of tubes. I did find a couple NOS tubes for very cheap so I bought those just to have. I like this tv set a lot I think I need to recap it before I regret waiting too long and one shorts out. I've seen that happen on tube amplifiers. Not fun.

Here's some pics of the schematic and list of tubes. I'm not sure these will show on here but here goes nothing.

Well I guess the list is readable at least.

the caps used in zenith sets are pretty good, esp the film caps.

the ones that give the most trouble are the single black low value electros, like 5-10uf. Not sure if your set has those, I see them in later rectangle sets.

You can change the cans if want but I generally check them, and if they test good I leave them be.

Most of the time there is a problem with dirty tube sockets, sometimes cold solder joints on video amp tubes, and maybe those .1 and .15 1kv films (again not sure as I cant test them).

Best thing to do with a zenith is to use it. That seems to keep them happy.

Apologies in advance...:rolleyes:

Butthead: Hey Beavis, can you reach around and turn up the BUZZ control on the back of this really big TV?

Beavis: Like....there's also this one that says "color killer"...what will that do?

Butthead: Leave that alone Beavis, it could transport us back to the old days of black and white!

.

If you see any white tubular caps or black tubular ones (usually striped like resistors) I'd suggest changing them. Orange drops, and other lookalikes tend to be good and should be changed only if after other work and checks the circuit they are in is misbehaving.

What do you use to check or test the caps?

I have a pair of smart tweezers it tells me the capacitance. But does not test them.

I have a old Sprague tel ohmike tester but no clue if its useful or works.

that tel ohm is the best! It may need caps itself but once working very nice.

The thing you need to test is leakage at rated voltage. Most old testers have an eye tube, IIRC the tel ohm uses a meter to show uA leakage.

They also test value (capacity). You have to be careful on low volt electros, as the test voltage may damage them, but for most vintage stuff its should be your go to tool.

I generally test the old cans and then compare to a new cap. If they test nearly the same, I assume the old is good to go and just hook it back up. Thats the one thing you need to do is remove it from the circuit, unlike modern ESR meters.

Post up a pic of the cap tester so I can see exactly what you have.

It's a TO-5 I'll take a pic soon

Here's the cap tester and some other stuff I have.

And more random testers I have. Let me know what's junk or good. Either way they make for a nice display.

the cap tester is TOTL, should be serviced and used.

Thanks Dave! I found a manual online for it. It don't seem too complicated to go through and calibrate.

if you decide you don't need it, clean up the tel ohm and get it working, list it on ebay, those bring in $$$. Go look at some completed sold listings.

Wow one sold for 200 bucks and as is condition. It's gotta be good to have if people pay that much. I got it years ago as a lot sale at a flea market for like 30 bucks. Hopefully it works still.

All eye type cap checkers I know of are old enough to need a recap to work PROPERLY....The good part is most have fewer caps than an AA4 radio so the recap is a breeze to do (less than a half hour going at a good pace).