Rebuilding disintegrated deflection yoke covers
 

As many of you are aware, many early color deflection yoke covers were made of a plastic that was prone to disintegrating over the years. The plastic used to make these covers is a molded thermoplastic that is made with nitorcellulose and camphor. It's called Celluloid. Here is a link to information about this old type of plastic which is not used much anymore.

http://plastics.inwiki.org/Celluloid

So the question is.... What can be done with the disintegrated celluloid deflection yoke covers. The answer is nothing... you must fabricate new parts from scratch.

This essay is a tutorial on how you can make replacements using easy to obtain user friendly materials.

The material I am using is model builders Styrene. I get it from Walthers model train supply but most hobby shops carry it too. It is made by Evergreen. I use .080" thick for the round discs, and .040" for the edge material.

Cuting the styrene is very easy. All you need is a utility knife to score the styrene. Then you place the score along the edge of a table and bend at the score. The styrene will snap where you score it.

Gluing, or more correctly "fusing" styrene is very easy and fast. Styrene will fuse with a liquid cement that sort of melts the styrene. All you have to do is hold the two pieces together and let the cement seep into the joint. In a couple minutes the joint will hold and in about an hour the joint will be very strong.

Here is how I rebuilt a delfection yoke for John Folsom's very rare 21" 1956 Motorlola that is in the process of being restored. Thumbnails 1 and 2 show the condition of the yoke as I received it.

The first step is to carefully disassemble the yoke so it can be worked on. In this case, both the back cover and the body of the yoke that the cover mates with, were totally shot. (thumbnail 3 is the disassembled yoke)

I started by building the body first.

First step is cutting a square peice of .080 thickness styrene about 1/2" larger than the diameter of the cover. I find the center of the square and drill a 3/8" hole. Then I mount the styrene in my lathe and turn the outside diameter to the correct size. (thumbnail 4 and 5) Then I reset my lathe tool and cut through the disc to make the correct diameter for the hole in the middle of the disc that will go around the body of the yoke. (thumbnail 6)

The disc is now ready for attachments of the edge pieces. The edge pieces are made of .040" thickness styrene. I cut 2 strips 1.125" wide by 21" long. I drag the strips of styrene over my thumb to creat a curvature in the plastic. (sort of like when you drag a ribon over the edge of a scissors to make it curl) Then I place the strip of styyrene around the circumference of the disc, and trim the strip to the correct length so the ends of the strip meet precisely.

Before attaching the edge strips, I took the disc and scored a line across the disc in the exact center so that LATER ON I can snap the disc into two equal semi-circles.

It is now time to attach the edge strip. Take a piece of scotch tape and join the ends of the edge piece together to form a circular ring. Place the ring around the circumference of the disc, making sure that the disc and the edge strip are flush to each other. Then apply the liquid cement and wait for the disc and edge strip to fuse together.

When the joint is solid (about 30 minutes) I took a tin snips and cut through the edge strip at the exact two points where the score I made previously on the disc, meets the edge piece. Then I snaped the disc into two halves. (thumbnail 7)

Edges of the parts are always made of two strips of .040" thick styrene bonded together in a fashion so as to stager the glue joints. So now I attach a second edge strip as shown in (thumbnail 8). AFter attaching the second edge strip to one half of the part, I installed the two semi-circular parts around the body of the yoke, and then I fused the edge strip to the second half of the part, thus joining the two halves of the body together into one solid piece. (thumbnail 9).

There are two terminal strips in this yoke. I used 5 minute epoxy and clamps to glue the terminal strips to the inside surface of the edge strip. (thumbnail 10)

The rear cover is fashioned in much the same way but it dosen't need to be cut in half like the body part was. The cover disc is made in the same fashion on the lathe, but it is about 3/16" larger in diameter and the center hole is smaller. The edge strips for the cover are also only 5/8" wide. Two edge strips are also used to make the edge of the cover, just as was done for the body part. Additional holes were drilled to accomodate aditional hardware that needed to be attached. (thumbnail 11 and 12)

Thumbnail 13 shows the completed deflection yoke with it's newly installed covers.

When attaching hardware such as screws or other fasteners, always use brass, aluminum or nylon fasterners. Never use any steel, or other fero-magnetic materials that will disturb the delicate magnetic fields that are createc by the deflection yoke.

Your deflection yoke may be different from this one, but the basic principals used on this project can be applied to almost any deflection yoke that has a disintegrated celluloid cover.

I hope this will be of help to some of you. Good luck!

Bob

Very impressive Bob! Now I know who to get a hold of when I get a rotted yoke.:yes::thmbsp: It looks fun, I might just try it myself, come to think of it, I may have a set in the garage with a rotted celluloid cover.

+1 :yes:

very impressive work, well done! You'll definitely be on my list to call when I need one rebuilt.

I was just brainstorming this week trying to think of a solution. This is much better than anything I thought up! This was also very common on bw sets. I have a mid-50s Motorola bw tv in the same shape-a good candidate for this!

That is simply outstanding, Bob. IOU.

This will motivate me to take on this set for restoration. I have pulled the CRT and am sending it to Hawkeye for rebuilding. Here are a few photos of the scruffy old girl. The cabinet is not great, but as it is a masonite type fake wood grain, I will probably just leave it alone. I still loops pretty good from the front.

Do any of you have original Motorola service data on this set? It is chassis TS-905, model 21CT2. I would be happy to pay for a good copy. While I have the Sams, I would like to gat the Motorola service data, as it should have a bit more detail than the Sams.

Awesome set John! I am envious:)

I checked, and my info consists of the Forrest Belt book that starts with TS-907 - sorry I can't help. Awesome set, indeed!

Here are a couple shots of the rear cover for the yoke on my 21ct55 that I just rebuilt recently. Different yoke design, same methodology used to create a new cover.

In my vast pile of junk upstairs I have a channel knob for this set. Upsets me every time I see it, thinking how somebody around here had one of these once...and all they saved was that knob!

I'm going to go digging through my Motorola service literature. I don't think I have it but it's worth a shot.

I smell a cottage industry coming into fruition....:thmbsp:

Thanks guys for looking for the service data. Bob, you may have a second career in styrene! :-)

Excellent work and write-up Bob. I was just thinking over the holidays how to repair my crumbling CT-100 yoke and this is the perfect solution.

excellent professional work,

Good work. I have often wondered how to fix this. I have saved your instructions and pictures as a guide.

Excellent work! Perhaps you can devise a way to do the B&W Yoke covers with the centering magnets attached to them?

It's a big problem on the RCA 8" portables, they distort badly and the magnets are only held on by a small rolled over lip.

Great job Bob!

Could you share with us the name of and where you got those clamps you used? I've never seen those before, but they look like they could be handy for many small projects.

Could you also share with us the item numbers for the Evergreen styrene sheets you ordered? I searched the Walther's site and they gave me over 1,900 choices for Evergreen styrene sheets.

And thanks for sharing with once again.

I'm having that exact problem with my 8" RCA right now. It started pulling in from the right side. I thought it was the horizontal output tube but it wasn't. One of the centering rings had slipped off of the yoke cover because it is warped. I can't find a new yoke so I am trying to buy a complete set to salvage for parts. So far, that's the only weakness I've found with these sets. Rebuilt yoke covers for this model may become about as sought after as the rubber masks on the 7" Motorolas.

OK Jim, here you go

Go to Walthers.com

Evergreen black styrene sheets

.080" stock number 269-9117
.040" stock number 269-9115

Plastistruct 3 ounce bottle of bonding cement solvent

Stock number 570-2

Good Luck!
Bob

I don't know what the yoke looks like for the 8 inch RCA. Could someone please post a couple of GOOD photographs so I can evaluate the issue. Perhaps I can devise a method to rebuild them.

Here is a link to Kant-twist clamps For this project I used the 1 inch size.

http://www.amazon.com/s/?ie=UTF8&key...l_67lni58w5i_e

I am not a fan of small screen sets so as a result my knowledge in this area is next to nothing.

Bob

Thanks Bob. That Styrene and those clamps may come in handy for more than just yoke repairs.

Bob, here are some pics of the RCA 8" yoke cover.

Note the notches, the yoke is clamped in place by a pivoting fork type thing, the notches are there so the yoke can be adjusted with a screwdriver, same with the notches on the magnet rings.

We could get by without the notches, it would just make it a little more difficult to rotate the yoke, putting the magnets on the cover might be a bit harder, there is a wave washer between them to keep them from rotating too easily, I'm thinking they would have to be put in place then the plastic hot rolled over them?

I think the front side looks do-able. Not easy, however do-able. It would probably be necessary to machine a PVC or Styrene insert with a flange lip to slip the magnet rings onto and then insert the assembly into the hole in the center of the cover while fusing it onto the styrene. Certainly a lot more involved than a conventional yoke cover, but with a lathe and a mill you can make almost anything.

How do the latch tabs on the back edge relate to the part they mate with? Do the tabs simply latch behind the body that the cover slips over, or do the latchs hook into some sort of notch? I guess a photo of how the latch tabs relate to the mating part would be in order.

Bob

Fantastic project work, Bob. I will keep your notes handy if I have to do a restoration like yours.

The tabs snap on to the phenolic board on the back of the yoke.
A replacement wouldn't necessarily have to snap on, it could be glued with some Silicone but there would have to be some tabs or else a recess for the yoke to fit into and keep it centered.

8" RCA Yoke Cover
 

I would definitely be willing to pay for a replacement yoke cover for this model. It is a common model of high build quality so there will certainly be a need for these yoke covers.

I see this is about repairing TV's. I really did not read it all. I thought you might like to know I saw a unbuilt Heathkit color TV kit on the Bay for auction.

Greg

Thats the one. That would sure be a butt load of soldering! LOL