maggie roundie
 

hey all, this maggie i have all of a sudden i turned it on and there is no color b@w only then the color bars start to fade in and a few minutes later the color is fine. in the beginning it was missing a color then it popped in but now its all the colors. does this look like a demod problem or a tube?

Bad crystal/6GH8
Try 6KE8 instead of 6GH8. You can adjust the osc coil but if the crystal is going bad it will continue to drift. I keep a stock of them because most bad so often go after awhile use

the crystal being bad would allow the color to sync up after a few minutes? would these crystals be standard, 3.58mz or were there others. this chassis is a ctc16 clone.

Exactly, drift as it warms up. Any of those 3.58 crystals seem to work. The modern small package ones work fine and dont have silver in them so they should last forever. timmy flavored :banana: bread

ok well if the tube dont work then i guess i am pulling the chassis. but if it has a different number on it other then 3.58 then i guess i should get that one, if i can.

I have, i can send to share one with you.

Classic symptom of 3.58 oscillator drifting, you get rainbow bars. Phil is intimately aware of this problem.

There can be 3 reasons why this happens:

1. the crystal is going out, and the reactance tube can't pull it in to lock solid
2. a problem with the oscillator circuit itself (try twiddling the frequency coil near the tube)
3. alignment is so far off that the 3.58 information contained in the signal is too weak for the set to lock on to

Of course check the tubes, but you'll likely find a bad crystal or the oscillator coil out of whack. When you tweak the coil, you have to ground the signal coming from the phase detector or it'll just wander all over the place. You should see the rainbow bars float by slower and slower then they will lock in. Right before it locks, you'll notice the number of bars is getting smaller and smaller as the frequency gets closer and closer to being right.

Maggie Roundie
 

Agree with all the above. Also check all caps and resistors in the color sync circuit while you are at it, and clean the tube socket contacts.

I agree the short answer is most likely the crystal.

In answer to your other question, I don't think any color sets of the old variety ever used a crystal with a frequency of anything other than 3.58 Mhz. Especially not Magnavox, RCA, Zenith, Sylvania, GE, Curtis Mathes... you get my point. :D

would you know if moyer carry these crystals or are they a specialty item.

Nte359 or was it 358. Super common any electronics store or ebay.

also try the color killer tube, I had the same problem and it was that tube, otherwise you looking at component level troubleshooting in the color circuits

I have been having the same problem with my 1981 Magnavox T815 and everyone ignores me when i ask a question. Been asking for months.

Firebird,
I went back and looked at your posts. You have not been ignored. You have been not following many of the suggestions made, and have been wildly replacing things with no diagnosis.

If you would follow the repeated suggestions to get a schematic and take some measurements, you would have a much better chance of fixing what's wrong, and not creating new problems, which your scattershot approach seems to be doing.

Slow down and try to diagnose your problems first - people here can help, but only if you pay attention and work more methodically.

also you have a solid state set.much different that the roundie.in this forum are the greatest techs alive and they are always willing to help anyone.relax,post pictures when you can and your problem will be solved.this is like magic and treat it that way!

I'll add solder joints to that list. On my Silvertone CTC15 clone it would come on good then within a minute go to looking like those screen shots above and soon after go to a monochrome picture with all saturated color elements displaying as green. After running for half an hour normal color would pop in. I lived with it for about a year before a PS cap I had already replaced once failed. While I was in there to fix that I resoldered all the chroma reference osc. traces on the board...After that(and a tweak to the osc. coil slug) the color synch has been ROCK solid.