CTC-7: Convergence, Convergence, Convergence - Videokarma.org TV - Video

jbeary · #1 08-12-2006, 10:52 PM

Hello All,

Can anyone let me know how come I can’t ever get a perfectly round dot from my dot generator? It’s not the dot generator because it works fine on the new TV which is perfectly converged… Because I can’t get a good dot, I can never get really good convergence and it’s making me crazy.

Could this be caused by having the elements out of whack? Can anyone post a diagram or pics for a CTC-7 neck; maybe with some measurements just to make sure? I get really good purity, but each dot is a different oblong shape. And while I can more or less line them up, the convergence is always off on one side of the screen or the other toward the end of the process.

I’m hooking up the generator through the tuner but no matter how I tune the fine tuning; the dot shape remains the same. Should I be going straight into the video signal to eliminate this? If so, can some one please let me know how to do that on a CTC-7 chassis with that horizontial trigger thingy?

THANK YOU ALL in advance for your help.

Jeff

***Eric H*** · #2 08-13-2006, 12:16 AM

Hi Jeff, I don't know about the dot shape but I seem to remember convergence problems on these sets being caused by a bad Selenium rectifier on the convergence board? Could be wrong, someone please correct me.

If you don't already have one there is a factory service manual for this model posted here: http://www.vintagetvsets.com/schem/ctc7-small.pdf (right click and save or you'll be stuck for a while, 8 meg file)
It has all the info for setup.

Eric

kx250rider · #3 08-13-2006, 01:11 AM

Typically the dots aren't round, due to various SLIGHT tuner and IF problems, and also due to slightly weak CRT or poor video response. Try turning the contrast way down and see if they get more circular. Also, if the TV focus is off, it will malform the dots. But no matter what shape, you can still use the dots for convergence purposes. They just need to be sharp enough.

As far as placement of the components on the neck, you need to refer to a diagram. I could try to explain, but a printed diagram is better. I'm not sure what effect on the generator dots mis-installed neck components might cause, but I can say for sure that those things need to be right in order to get convergence and purity. Any of the RCA factory manuals, or the Color Pict-O-Guide, or any early color TV repair textbook will have a diagram.

Charles

Chad Hauris · #4 08-13-2006, 01:29 AM

Also make sure the vertical linearity is good...if you have weak tubes or caps in the vert section and have the vert height control at maximum you may be getting distortion of the vertical waveform.
Make sure too there is not a pot on the convergnce board which has an open segment in the resistance element.

jbeary · #5 08-13-2006, 11:43 AM

Hello Guys,

Thanks and I'll try all this stuff. I never did replace the selenium rectifier on the convergance board, so I'll try that too. Thanks so much for pointing me to a factory service manual. That's better than the Sams I have for sure!

Will let you guys know the results.

Reards,
Jeff

vintagecollect · #6 08-13-2006, 06:30 PM

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reeferman · #7 08-13-2006, 09:43 PM

Jeff,

Don't be to hard on yourself expecting perfect convergence because it won't happen. This was the first roundie to have the "modern" convergence board.

I doubt the selenium is bad. I tried putting in the more modern style in (like from a CTC-16) but not once did it make a difference.

To get a better dot/crosshatch adjust the brightness along with the contrast. Try injecting a video signal vs. running it through the antenna terminals

Have patience and enjoy. Good luck.

Phil

Chad Hauris · #8 08-13-2006, 09:59 PM

The round sets are capable of as good of convergence as modern sets if set up right...the convergence is actually easier to set up on the rounds rather than the rectangular delta gun sets.

reeferman · #9 08-13-2006, 10:14 PM

Chad,

I agree very much with what you say! All I'm saying to Jeff is not to expect the set to perform like it did 40 yrs ago

Phil

jbeary · #10 08-14-2006, 01:41 PM

Hello again All,

I do think some of you guys are right and I shouldn’t beat myself up over a few little shadow marks. Like my dad said when he first saw the TV working; "when you've been looking at black and white your entire life, color looks pretty good" (I’m not giving up my B&W though). Just about everyone that sees the TV working comments on the color (rich and vibrant) and no one has mentioned seeing a few weird artifacts on the screen.

In 1958 I guess that most people were just happy to see a color broadcast. I know that most if not all of the issues that plagued the earlier color sets had been worked out by the time my TV was designed and that there were probably only a handful of color sets bought in 1958 that were installed correctly and that people most likely settled with a mediocre set-up. However, it does not make sense to me that I can't get perfect convergence across the entire screen. The way I'm thinking is that my set should work at least as good if not better than it did when it was new. I mean, I've replaced about a 1/3 of it alone with swapping out all of the capacitors. And rarely have I done a complete overhaul of any TV and not had to adjust something and this one is the same. Everything from the power supply to the tuner works GREAT except for the convergence being off.

Now, like I said before, I may be being nit-picky but every time I go through the convergence process, I get differing results. I start with the purity adjustment and go from there since I'm pretty confident that all of my screen controls are balanced. It looks very in focus to me, but I'm definitely going to fiddle with the contrast as well as the brightness and focus controls. I wish someone would tell me how and where to inject the video signal from the generator and how to use the horizontal trigger. I've read documentation, but the last thing I want is to blow up something in the video chain or my dot generator. So if someone has hooked up a generator this way before on a CTC-7, please let me know how you did it. I've always read that I need to put it on the second IF amp and use some RCA WG-306A adapter. I'm in the dark because I lack the knowledge and the confidence.

I'm also worried about the placement of the yoke, convergence yoke, purity rings, and lateral magnet. The plastic that held the lateral magnet disintegrated from me fooling with it too much, so I made one from some heat shrink tubing which seems to work okay. The point is; I've messed with these things so much I'm afraid that without seeing where exactly they should be on another set that works perfectly, I may as well just abandon the idea of having perfect convergence. I know that they're in about the right positions, but I've noted that as soon as you bump a purity ring, the shape of the dot changes. So very often I would start with good purity and then bump the magnet ring mistakenly and change vertical or horizontal convergence without being aware of it. Then I'll go onto doing all the rest of the convergence steps only to be dissatisfied with the results. The big question is where do I put the convergence yoke? The center convergence magnets should be directly over the poles, but I have no idea where the pole pieces are because the inside of my CRT is shadowed and the outside pole pieces cannot be viewed from the glass envelope. If anyone can let me know how far forward from the pin side of the socket I'll need to go with the convergence yoke that would be great!

I printed out the 50 page "Service Clinic" for the 800 series that someone sent me a link to and it is packed with useful information that I've yet to see compiled in one place. So THANK YOU for that. If you guys have anything else that you can send, please forward it to jbeary@cox.net. I’m also available to answer questions about basic TV restoration if anyone out there needs help with something. I wish I had more time to devote to a website, but I’m unfortunately over-burdened!

THANK YOU ALL AGAIN!
Jeff

blue_lateral · #11 08-14-2006, 05:44 PM

You really need a picture from one of the books, but I'll try.

The yoke goes anywhere for now. there are pole pieces on each gun. The convergence electromagnets go over these, not the sliding magnets. There is probably a coating on the neck blocking your view. Try to look up in there and see them. They might be under the pink stuff inside the neck (if you have it). In any event, look forward and try to see them. Center the convergence yoke over them, blue on top. They are the same thickness as the convergence yoke, so if you can see one edge of the pole pieces, you can figure it out.

Next comes the purity rings. They might have more plastic on one side than the other. I forget which way, but you can sort of tell because the rings I think. The extra plastic probably goes forward. The rings go over a gap between the elements of the electron guns. This is going to put them really, really close to the static convergence magnets.

The blue lateral comes next. there is a pole piece on top of the blue gun for this. The magnet is centered front to rear over this pole piece, but twisted to about the 2 o'clock position on the neck. If you have the blue lateral that turns, the short part thats through the bracket is what goes at 2 o'clock. If you have the bar magnet, the magnet goes at 2 o'clock. If you have the one with a little bump of a magnet strapped directly to the neck, start out at 2 o'clock, and adjust by changing the clock position.

If you have something in the wrong way, like the purity magnets, you probably cant get blue lateral forward enough to be over the pole piece. This stuff is really crammed together when its put on there by the book.

The blue pole piece is at focus voltage (6kv) with the set running, and the blue lateral is usually grounded. If you can maximize the distance between the blue pole piece and the grounded bracket by adjusting clock position, It's probably a good Idea. Probably only possible on the bar magnet kind.

All the best,

John

jbeary · #12 08-14-2006, 06:11 PM

Thank you all for trying to help me. I'm going to post a picture of what I currently have because it sounds like I have everything in the correct spot but I still want to make sure. I look forward to someone telling me that I have it all wrong but so far it all seems right. I just can't see the pole pieces inside the neck and this is what I feel is throwing me. I've tested the position of the convergance yoke by sliding it back and forth as well as side to side and everything nets a different result. Of course, I'm looking for the best one

6K on the lateral magnet band??? YOWAZA! I hope that I don't lose that ground. I better check the solder joint on that thing because when this sucker shocks you, it does it real good.

Also, if anyone wants to chime in on injecting the video into the 2nd IF amp, please do.

THANKS AGAIN GUYS!

reeferman · #13 08-14-2006, 06:15 PM

John,

I can PDF some stuff to you from the RCA Service Manual. You can get good, but I doubt perfect is achieveable. There are just to many dynamics involved (like the shadow mask). Play with the set, experiment, gain some experience, and have some fun.

Phil

Whirled One · #14 08-14-2006, 07:52 PM

Quote:

Originally Posted by reeferman

You can get good, but I doubt perfect is achieveable. There are just to many dynamics involved (like the shadow mask). Play with the set, experiment, gain some experience, and have some fun.

I gotta agree with Phil here-- I wouldn't expect to get absolutely *perfect* convergence on an early color set no matter what you do or what you replace. Try to get it as good as you can, but don't expect perfection. This was a common comment/criticism even in _Consumer Reports_ reviews on color sets through the 50's. Convergence generally improved with each generation though. At least the CTC-7 can't be as tricky in that regard as the CTC-5, which still had a metal-coned CRT and needed those edge purity magnet adjustments, along with DC static convergence that tends to drift according to line voltage. Anyway, have fun, but don't feel bad-- I doubt even the RCA service folks could get these things totally perfect.

roundscreen · #15 08-14-2006, 08:01 PM

Jeff
The round color crt is vary fussy when it comes to magnetic fields in and around the room. Every time I move a set it will change the purity and convergence and I have to realign the crt. I have found when you point the neck of the crt to the south and the screen north [ or neck north, screen south } when doing a alignment it will be easier to get purity and convergence right, But not perfect. {The blue vert lines are the ones I have the most problems with.} Put the set were you are going to watch it, Demagnetize the crt and set. Do purity and center convergence. Then cut off the blue gun {turn down blue screen and drive} and converge the red and green first. Then converge the blue to the red and green. Reeferman is right, You may have play with the set to get the experience. If you get lost , Take a break for a few days and then attack at it again.
Ed