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#46
11-24-2006, 10:00 PM
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No schematic in front of me.... and I won't be where the schematic is until at least tomorrow.
Here's a couple thoughts, though. The plate voltage change on the r-y amp is probably just due to the grid bias changing. In other words it's probably a normal reaction. As for the plate voltage changing on the previous tube, it might be unrelated. It's tough to guess without my schematic. I think the grid bias is the big thing. The slowly drifting thing is kind of strange. I have had mylar caps fail in a color matrix, but the intermittent was sudden. The cap is a possibility, though. Is it a purple mylar thing? Ceramic disc? It would be a good explanation for where the extra voltage came from on the grid, as the other end is connected to the plate voltage of the previous tube, and no DC should be getting through there. If the capacitor leaked, it would raise the grid voltage. The grid resistor might be a better bet. If it changes value with heat, maybe that would do it. Drifting resistors are usually slower. I would lay a soldering iron on it and see if you can make the change. If the resistor looks like it is made out of something that would melt if you did that, then you could lay a soldering iron on the wire next to the body of the resistor. If you lay it on the wire instead of the case, the soldering iron would have to *not* be grounded I think. My soldering iron is grounded, so I would instead probably hang an ohmmeter across the resistor and heat it up with the set shut off. What this really sounds like to me is a gassy tube. You get slow grid bias change over time. I read up above that you switched the tubes to eliminate this, right? Are you sure they really got switched? 
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#47
11-24-2006, 10:00 PM
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...
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#48
11-28-2006, 12:56 PM
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John, Had the chassis powered up last night on the bench for about an hour. Seems that the grid bias on the r-y amp is staying at the higher 12 volts now... no more back and forth going on. Perhaps something decided to fail completely.
Quote:
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Again, thanks for the tips/suggestions! Wes
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#49
11-28-2006, 05:45 PM
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Did the soldering iron test on the 1 Meg grid resistor (R730) with the set off. Cold, I am measuring 1.18 Meg. When I apply heat with the iron to one of the leads of the resistor, it responds immediately by increasing resistance. Got up to > 1.4 Meg in a few seconds and still climbing when I let off the heat.
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#50
11-28-2006, 07:43 PM
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I'll bet you found it.
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#51
02-11-2007, 05:23 PM
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Quote:
 So as much as I don't like this method, I decided to try a shotgun approach. Changed all of the capacitors and many resistors in the chroma section hoping to find the problem with the red. (see picture attached)Still no reds, voltages still slowly varying and reading to high.  I have no clue what to try next...  Just tried swapping the 6GC7's around again. Two of them are brand new and the other tests as new. No change. Only difference now is that I never see any red in the picture at all.My set is teasing me... I have a beautiful picture except there is no red. I'm stumped... Ready to consider shipping the chassis to an expert for repair. Does anyone know of a good vintage color television technician who can repair a CTC11 chassis? Or, I am open to any suggestions. Thanks John and others who have helped so far. Wes
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#52
02-11-2007, 09:17 PM
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Don't have a CTC-11 schematic, but since you are grasping ---
IF it's like a CTC-7 with X and Z demods (in one tube), have you tried checking around the demod tube for intermittent voltaqes, or replacing the demod tube? If the picture really is still black and white (not cyan) it's hard to see how the R-Y amp could cause the problem without changing the gray scale tracking. So I'd think maybe the X demod circuit could be the culprit. Apologies ahead of time if this takes you on a wild goose chase - just thinking out loud.
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#53
02-11-2007, 10:45 PM
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Thanks old_tv_nut! Would you believe that all appears to be working great now??
 After reading your post, I pulled out my CTC11 schematic to check the demod tube... Yes, the X and Z demod are combined into one 12AZ7. The original 12AZ7 from my set tested to be very weak on my tester, so I had replaced it with an NOS Philco tube from Antique Electronic Supply. But, when you recommended replacing the demod tube, I decided to plug in the original RCA tube just to see what happens.... Powered up the set and now have RED, GREEN, BLUE all working! Beautiful picture. No sign of the red fading in and out.... watched for 1/2 hour and all was good. Will try a longer test tomorrow.A hard lesson learned? NOS tubes can be bad out of the box? Don't assume it's good just because it's new? A tube that tests bad on the tester can still work OK? Don't forget the basics? Etc., etc., etc. Anyway, thanks again for thinking out loud!  I'll post some new screen shots when everything is put back together and I'm sure it's working correctly. Wes
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#56
02-11-2007, 11:50 PM
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#57
02-16-2007, 11:17 AM
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Hey Wes
Hey Wes,
When do I get to see the set??? I got a similar issue with a late model Zenith Cromacolor. No horizontal sync but everything tests good. It's like I have three sets of tubes for this thing, they're all compactrons and they all test good, but I swap and swap and nothing. I feel like you, on a wild goose chase replacing resistors. It feels good to get it going though and I'm glad you spent the time to do it right! NICE! Now how's that convergence! Also, I have a video amp as well as one of those "video stabilizers" if we want to try knocking out retrace lines over at your house. Since we rip all of the media we want to keep, I always have media without Macrovision. I can burn some for you if you're looking for anything in particular. Just tell your brother what you'd want and the next time he's over, we can burn some stuff up. Or just see when he'll be by and come with and look through what we have (although I wish more were in color). I'm just wrapping up the house work and hope to get back into the cave soon. I have to pull some cable and Romex into the bathroom because I promised myself I would put a drop in the can this winter so I can go in there and click on something when I'm bored with reading the paper. Maybe after that we can get it together to see about getting a space to display some of our stuff. It'd be nice to have our own museum! Now that would be cool. Yours, Jeff
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#58
02-22-2007, 10:12 PM
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Hey Jeff, great to see you hanging around here. Yes, I would very much like to try your video stabilizer to see if it helps with the Macrovision interference. Seeing those retrace lines fade in and fade is not cool! May take you up on your offer to burn some DVD's. (desperately need a new computer over here.) I did go through the purity and convergence settings per the service manual -- very similar to the settings on your set. Got stuck near the end of the procedure since I can't find my plastic tool to tweak the slugs for the right side adjustments. May get you to come over and give me a hand going through the convergence again. It's tough for me to see the center of the screen in the mirror when adjusting the magnets... All-in-all, the picture looks nice. What's the story on your Zenith set? Must be a recent find? Hope you will get it going. The members of the Television forums are simply great. Always nice to have the pros looking over your shoulder!
Wes (btw, Thanks for the records. Right up my alley.)
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#59
03-24-2007, 06:09 PM
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Okay, you finally shamed me into it :-) After a long winter's nap, I pulled the chassis on my CTC-11 and began preparations to replace the electrolytics. Took a few minutes to find C5 and C7, dinky caps buried inside a shield under the chassis.
I'm going to try to restuff as many of the cans as possible, although the 160uf caps that I got are awfully chubby. Phil Nelson
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#60
03-25-2007, 07:42 PM
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Phil, I had also considered restuffing the cans on my set. Things got real crowded under the chassis where I mounted the replacements. If you ended up with the same 160uf caps as I did, I think they were physically too large to fit in the original cans. A good solution may be to restuff the original cans with the smaller values and then mount the 160's underneath? By the way, I didn't experience any interference as a result of moving the electrolytics underneath...
I hope you will do one of your famous write-ups on the CTC11 set and post to your site. Always enjoy reading your restoration articles. Wes
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