CT-100 color sync issue?

[Phil Nelson]

Dorothy's back, too.



Other issues remain, but color sync isn't one of 'em.

The most recent set of color bars were from the test pattern DVD. I just tried the generator again, and with its stronger signal it's easier to get better color bars -- including magenta, for instance, and a deep blue.

I'm playing the TV for a few hours -- Gone With the Wind, for a change -- to see whether this improvement sticks. Then I'll pull the chassis back out and take another look at the color circuts while dealing with some other stuff. I'm inclined to set the generator aside and use the test pattern DVD from here on out. The ultimate goal is to watch movies and TV, not generator patterns.

Thanks,

Phil

[old_coot88]

Originally Posted by Phil Nelson

Bill, do you have ESP? About 20 seconds ago, I just finished uploading this fresh picture of the TV with original crystal back in place.

No ESP. Darndest thing though, i don't remember ever seeing the xtal cause loss of sync. Of course that's been nearly 50 years ago, and xtals might go bad over time. Evidently yours didn't.
A couple of little tips worth bookmarking.. the reactance coil is the primary 'color sync' adjustment. To tell if the color osc. tube is weak (even if it shows "Good" on a tester), have the set running with a normal in-sync color picture. Shut the set off for maybe 5 to 10 seconds, and turn it back on. It should come on in sync. If it comes on with color bars and takes a while to lock in, the tube is weak.
The same test can show a weak horizontal osc tube too. Bill(oc)

[miniman82]

Bear with me here, I'm just gonna think out loud for a second...

Looking at the color bars, it appears red has bled (or shifted) over into magenta, and blue has bled (or shifted) into cyan. Looking at the vector described on your site, and taking into account the way the demod and matricies are wired in the CT-100 schematic, I'm lead to believe you may have an issue in the demod/matrix section of the set. Here's what I'm thinking: if the +Q signal were 'weak' in signal strength, would not there be more red (given that +I stays the same) leading to the mostly red bar where there ought to be magenta? It would also explain why the bar on the end that's supposed to be blue has shifted more towards cyan, since it takes -I and +Q to make blue (lack of +Q with unaffected -I).

Again, just thinking out loud and I'm probably wrong here. But if this were my problem, I'd start poking around with an ohm meter for drifted resistors in the I/Q demods (+Q specifically), or possibly weak demod or adder tubes.

[Phil Nelson]

Thanks for the tips, Bill. I like those practical tricks that come from experience and might not be found in any book.

Miniman82, you're right, even though the color bars have stopped rolling, they're still half-baked. It would be a minor miracle if they weren't, considering the unscientific horsing around I've done lately. I intend to check a bunch of things when I take the chassis back out. For starters, I'll redo the color AFC alignment with the original crystal and with the test pattern DVD instead of the generator. There are some unrelated little mysteries, too, but one thing at a time.

Regards,

Phil

P.S. The set remained stable while playing for about three hours. So far, so good.

[old_tv_nut]

Originally Posted by miniman82

Bear with me here, I'm just gonna think out loud for a second...

Looking at the color bars, it appears red has bled (or shifted) over into magenta, and blue has bled (or shifted) into cyan. Looking at the vector described on your site, and taking into account the way the demod and matricies are wired in the CT-100 schematic, I'm lead to believe you may have an issue in the demod/matrix section of the set. Here's what I'm thinking: if the +Q signal were 'weak' in signal strength, would not there be more red (given that +I stays the same) leading to the mostly red bar where there ought to be magenta? It would also explain why the bar on the end that's supposed to be blue has shifted more towards cyan, since it takes -I and +Q to make blue (lack of +Q with unaffected -I).

Again, just thinking out loud and I'm probably wrong here. But if this were my problem, I'd start poking around with an ohm meter for drifted resistors in the I/Q demods (+Q specifically), or possibly weak demod or adder tubes.

As long as we are guessing: Looks to me *mostly* like too much color and tint control not quite right. MAYBE but only MAYBE the I gain ( I believe there is an adjustment) is high, rather than Q being weak; or MAYBE the quadrature transformer is a tad off 90 degrees. Need to tweak these things step by step, since any one can throw the color bars off.

[miniman82]

Originally Posted by old_tv_nut

MAYBE but only MAYBE the I gain ( I believe there is an adjustment) is high, rather than Q being weak.

Excellent observation! There is in fact a gain pot for I, it's 2R361 in the schematic: http://www.antiqueradio.org/art/RCAC...CAManual9C.jpg

[Phil Nelson]

Yes, this wonderful TV has more adjusters than a barrel of monkeys and they are interactive. I have gotten best results by following the manual procedures exactly, in the order given, even when I feel like Adjustment X might be unnecessary.

I haven't done any of the usual setup at this stage -- just stuck the chassis into the cabinet. Since I'm going to take it right back out to redo the color AFC & other things, I'll do the setup for real next time.

Phil