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  #1  
Old 07-23-2018, 07:55 PM
Techguy46 Techguy46 is offline
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Zenith 29JC20 21"--cataract and convergence

First big challenge is getting the cataract off the tube (21FKP22). The blear covers all but about the central six inches. I have watched a few youtube videos on cataract removal, mainly using heat. The tube is now out and sitting in the top of a garbage can. The plan is to set it out on a RILLY hot day, then if that isn't enough hit it with the heat gun. (I am in TN, so yes we have days in the upper 90's.) I would appreciate any advice or warnings concerning this operation.

The second big challenge is that the plastic frame for the convergence coils (and magnets) (looks like a 3-leaf clover) is busted in two places, so the coils are kinda ski-wacky. Suggestions for repair? I am guessing something like JBWeld. Or by some miracle are these available? What do I know?

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Old 07-23-2018, 09:00 PM
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There are two types of cataracts the green Halo and the moldy white. Green you can cut cold with a guitar string. The white you either heat or soak in water. If it is white and that far in it should be an easy fix.

You may be able to glue the clover. On my 29jc20 they just installed a newer style clover and spliced the wiring to the board.
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Old 07-23-2018, 10:09 PM
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For the "white" cataract, I think the water method is safest but it can take weeks. I've done this a few times; it doesn't work well with the "green" type.

I've done a number with heat, best with a decent heat gun. I actually did one on a dud (aired tube) using a propane torch and it seemed to work just as well though I'd be cautious doing it with a "live" tube. I also tried infrared bulbs on a dud one time and it worked well but the crt cracked underneath-too hot!
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Old 07-25-2018, 10:13 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Techguy46 View Post
First big challenge is getting the cataract off the tube (21FKP22). The blear covers all but about the central six inches. I have watched a few youtube videos on cataract removal, mainly using heat. The tube is now out and sitting in the top of a garbage can. The plan is to set it out on a RILLY hot day, then if that isn't enough hit it with the heat gun. (I am in TN, so yes we have days in the upper 90's.) I would appreciate any advice or warnings concerning this operation.

The second big challenge is that the plastic frame for the convergence coils (and magnets) (looks like a 3-leaf clover) is busted in two places, so the coils are kinda ski-wacky. Suggestions for repair? I am guessing something like JBWeld. Or by some miracle are these available? What do I know?

Thanks HUGELY
Techguy46
The set must have the original CRT. The CRT is RCA sourced, but it was numbered 21FK instead of 21FJ. Why?
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Old 07-25-2018, 01:54 PM
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Originally Posted by dieseljeep View Post
The set must have the original CRT. The CRT is RCA sourced, but it was numbered 21FK instead of 21FJ. Why?
Because they had to buy it from the one 'FK'ing supplier they never wanted to give business to.
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Last edited by Electronic M; 07-30-2018 at 10:06 PM.
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Old 07-30-2018, 08:24 PM
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reeferman reeferman is offline
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Cloverleaf

I have a NOS cloverleaf. Might reproduction be a possibility with 3D printers? It would definitely have to be flexible to work.

As mentioned earlier, installing the hard plastic convergence assembly is the way to go.

Phil

Last edited by reeferman; 08-05-2018 at 03:41 PM.
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Old 07-30-2018, 10:10 PM
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I have a NOS cloverleaf. Might reproduction be a possibility with 3D printers? It would definitely have to be flexible to work.

Phil
Sure it should be possible. There are 3D scanners and printers around, and a variety of types of plastic filaments available...Once it has been scanned and any needed adjustments have been made to the CAD file then it should only be a matter of selecting the best-suited filament and figuring out how many copies to make.
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Old 07-31-2018, 08:01 AM
iong iong is offline
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Zenith 29JC20

Anyone know if Zenith 29JC20 (First Zenith Color) Has as nice picture as a later roundy like 26KC20?
Perry
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Old 07-31-2018, 03:08 PM
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It was on par with my 25MC33 before I sold the MC...Granted I'm using direct video injection since the tuner IF needed work and I was not prepared to open that kettle of fish.
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Old 07-31-2018, 07:32 PM
iong iong is offline
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Zenith 29JC20

Where did and how you connect the direct color video input?
Perry
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Old 07-31-2018, 09:20 PM
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There was a thread on here where someone else explained it. IIRC (it has been ~3 years since I did it...) all I had to do for the video was unhook the outputs of the two video detector diodes from the set and connect the unhooked connections downstream of them directly to the center conductor of the video cable I used...This also defeats the RF sound circuits IIRC.
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Old 08-04-2018, 04:21 PM
Techguy46 Techguy46 is offline
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Progress!!

Nice hot day, set the tube out with a black plastic bag over it around 8 am. By noon it was around 150 deg all over the face (used one of those laser temperature meter thingies) and the lens popped right off! Easy peasy. I will try to post some pics.

Next step is thorough cleaning and sealing.
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Old 08-04-2018, 08:56 PM
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Nice work! When a cataract is that far in it is easy to fix...When one has just started forming to the point that 1-2" of the edge is cloudy they are not as fun to fix.

BTW is that a 5" SONY 1/2" EIAJ RTR videotape in the background of the first pic?
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Old 08-05-2018, 02:03 PM
julianburke julianburke is offline
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The 29JC20 chassis delivered very nice color pictures with a sulphide (green) screen. Back in the '60's I used to go to the Zenith schools when they would come to Knoxville and Graybar Electric would host these as they were the regional Zenith distributor. The Zenith field engineer we called "the Dutchman" would tutor these classes. He would always refer to the 29JC20 and his young son was touted to be a 29JC20 expert!


As for the "cloverleaf" convergence plastic mount, it was always a problem even way back then. Its' main drawback was that is was not "adjustable" with a screw clamp mount and it was the dickens to reinsert the coil & magnet components in this plastic ring that was not flexible. In doing so it always felt that you were going to break it. The worst part was to replace the completed assembly on the neck of the tube as it was VERY VERY TIGHT! If you had a loose CRT socket, you could also crack the tube or break one or more of the wires underneath to further the hindrance. Time, age and heat would always make it brittle and break as it had a short life span.


As for removing the faceplate on a bonded face, a rebuilding plant that I would work at on nights and weekends, we would place a clean scrubbed tube facing a large (2' X 2') natural gas radiant heater (about two feet away) and after about 10-15 minutes we would place it face up on a wooden box with a one foot hole and take piano wire with a wood dowel on each end then place your knee against the tube and pull the wire between the faceplate and tube and pull. Be sure to wear heavy gloves when doing this not to mention handling the hot tube from the radiant heater. It would slice through with ease. I DO NOT recommend using a hair dryer or heat gun as this will create hot spots on the glass as the heat applied must be uniform throughout the whole glass area and can be dangerous as if you get a very hot spot on the tube itself as it likely can cause the tube to implode depending on the ambient temperature of the area. Moving the heat gun around on the face is usually a losing battle as when you move it around, the spot you just heated will cool rather quickly as there is a large mass area on the face.

I hope this answers a few questions here.
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Last edited by julianburke; 08-05-2018 at 05:14 PM.
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Old 08-05-2018, 03:44 PM
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Julian,
You nailed it. I had forgotten what a "joy" those hard plastic convergence assemblies were! The original cloverleaf was much easier to work with, for sure.
Phil
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