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  #31  
Old 06-30-2015, 05:41 PM
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63bird 63bird is offline
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I sent a email. I'll go through the lot and see what I'm keeping.

So I have a crt tester and a supposed good tube tester coming in the mail.
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  #32  
Old 06-30-2015, 06:06 PM
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I have the Sams in PDF.
Send me a PM.
Phil
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  #33  
Old 07-01-2015, 12:13 AM
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I agree with Zeno. Replace K1 and K2 vertical integrators. VERY common problem.
Changed a ton of them.
Phil
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  #34  
Old 07-06-2015, 06:55 PM
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So I got some working test equipment finally.

I found a pin on the crt that was very corroded. I cleaned it up.

Crt tester showed a weak gun so I followed the rejuvenation instructions and all 3 are now in the good range. No shorts either.

The color is better but I'm not sure what my issue is so here's a short video. I'll find something else to play later on.

65 zenith color roundie troubleshooting: https://youtu.be/iFTNy6VR-AY

The Color bar generator was fun to mess with.

So now I can test tubes and do a little more now.
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  #35  
Old 07-06-2015, 08:51 PM
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zeno zeno is offline
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Try a blanking tube. There is both vert retrace & a white line
going down the left side.
Also be sure you can turn the brightness down. If
not it may need a set-up by the book, no big deal.
This set should come out quite nice. Keep in mind
even when new they are not bright sets, use in subdued lighting.

BTW the volume knob will have the Zenith color triad on it.
Tons around I am sure.

73 Zeno
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  #36  
Old 07-06-2015, 10:01 PM
DaveWM DaveWM is offline
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looks like some fold over on the left, maybe need the horz setup procedure. ( oops forgot zeniths dont really have a setup procedure other than adj the hold control for good lock, you could try just adj the horz hold of tube swaps below do not help)

Anytime I have issues like this I start with new horz out and damper tube, and horz osc.

also agree with zeno, you have to not drive sets too bright, esp if the CRT is not great on cutoff, or you get the vert retrace.

Test pattern generators are often not the best signal source. Be sure to test them on a known working set to make sure they are not the problem.

on vert size, 1st suspect would be the cathode bypass cap on the vert out (100uf), next I would go a head and replace the .1 1KV boost filter cap on the vert size pot. Any leakage there would drag down the voltage supplied to drive the vert osc. you could confirm this by checking voltages of the plate of the vert multiplier. I routinely change out those since I can't test for leakage at 1kv. Be sure to try a new tube 1st both the vert multivibrator and the vert output. Never assume tubes are ok, and you cant test them as you need to sub those.

Last edited by DaveWM; 07-06-2015 at 10:06 PM.
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  #37  
Old 07-06-2015, 10:21 PM
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This is the best pic I could get. It's actually pretty good.

Turning brightness down helped. I finally felt like the controls made adjustments. Where before it didn't do much at all.

I'm really thinking to recap all the can caps at a minimum. Or should I do all electrolytics?

I really feel like the Tuner it dirty is there a test point on the chassis I can inject a composit signal? Also any tips on cleaning it?

My 1963 B&W Magnavox has a perfect working tuner that keeps stations locked in very well.
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  #38  
Old 07-06-2015, 10:22 PM
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I'll buy the new tubes for it that you mentioned Dave thanks.
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  #39  
Old 07-07-2015, 05:08 AM
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Dont forget to order a blanking tube !

You can usually inject 1V P-P composite at the 1st video amp.

For tuner pull the cover. Hold a big eraser against the strips
& turn. Work your way down the tuner. Best to pull it
out so you can see what you are doing. Things get delicate there.
Can also check your FT mech at same time.

73 Zeno
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  #40  
Old 07-07-2015, 07:41 AM
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Where is the blanking tube located? I can't find it on either schematic that I have. I'm not sure what one is or does.

TV repair makes amplifier repair look easy.
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  #41  
Old 07-07-2015, 08:28 AM
DaveWM DaveWM is offline
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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
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  #42  
Old 07-07-2015, 08:35 AM
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Quote:
Originally Posted by 63bird View Post
Where is the blanking tube located? I can't find it on either schematic that I have. I'm not sure what one is or does.

TV repair makes amplifier repair look easy.
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
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  #43  
Old 07-07-2015, 10:02 AM
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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.
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  #44  
Old 07-07-2015, 10:29 AM
DaveWM DaveWM is offline
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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.
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  #45  
Old 07-07-2015, 11:24 AM
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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.
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