CT-100 color sync issue?
 

I'm guessing this CT-100 has a color sync problem, but I'm open to other theories. The color bars are bright and stable when I connect a pattern generator:

http://antiqueradio.org/art/RCACT-10...arsForGrid.jpg

When I switch to any other source, we get the same old rolling color bands, which are usually so faint that the picture looks almost monochrome:

http://antiqueradio.org/art/RCACT-10...licWizard1.jpg

Going through the color AFC alignment procedure didn't fix anything. You can see more pictures and read about other things I've tried in the updated article:

http://antiqueradio.org/RCACT-100Television.htm

Scroll down to the section, "First Picture With New Picture Tube."

I'm just about to take the chassis back out for another round of checks & tweaks. If you think I'm barkin' up the wrong tree, now would be a great time to say so :)

Regards,

Phil Nelson

Have you tried another Xtal? IIRC, over (a long) time they loose mass and frequency increases very slightly.
jr

Yea try swapping out the crystal. Its fairly easy and allows you to rule that out if nothing else.
I have ended up changing them on every old rca set I have.

I would change the crystal and then check to see if your generator is slightly off. (how old is it?).

One way to check is to hook up a meter to the color AFC control voltage in the receiver. (The set must lock up to both sources that you want to compare, though.) Then measure the control voltage with one source and then the other. Any diference indicates a difference in the frequency of the sources. Unfortunately, there are no analog stations to use as your standard of reference, so you will need to compare whatever local sources (DVD player, cable box, etc.) you have handy to your generator.

Perhaps the bar gen has a stronger output signal, and your other sources aren't strong enough? Might be a good idea to look in the tuner/IF for issues. AGC might also be to blame, or maybe the color killer? My CTC-9 will do something like this if the noise gate and killer are adjusted wrong.

Ditto on the crystal. Could be something as simple as a sync or demod tube.

Silly me, I thought I would just step over to my CTC-11 and borrow its crystal, but of course that's conveniently mounted under the chassis.

In the shop I found a board from a junked 1980s TV with a crystal. If I can unsolder that and add little leg extensions without burning it up, maybe that will do for a substitution test.

Say that I wanted to go nuts and buy a new one -- where to look? A quick romp through Digi-Key and Allied didn't turn up much. I don't care if it looks exactly like this one, as long as it has two legs that I can solder prongs onto somehow.

http://antiqueradio.org/art/temp/RCA...tal3-58MHz.jpg

Phil

You have PM.

Phil,

Look for a NTE358 crystal. It has the same style case but the legs are smaller diameter. What I do is wrap a layer of very fine copper wire around the legs of the NTE358 and then solder the layer of wire. If you use the right gauge copper wire to wrap with, you will add just enough thickness to the legs so they fit snugly into the crystal socket on the ct100. When you finish the nte358 will mount and look like the original.

Warning do not use a NTE358A

I looked high and low for the correct style as used in the ct100 and there are none to be had unless you find one in a junker set.

Exactly, NTE358. You need the big style, the small ones quickly fail under the high voltage.
I found some at the local electronics store that look like a big blue disc capacitor and they seem to hold up.

Thanks, now I know what to look for.

You're lucky to have a local store that carries components. I phoned the most likely place I could think of around here, and had to spell the word c-r-y-s-t-a-l for the clerk.

Trying the crystal I salvaged from the junk board was a waste of time. Made weak color bars and a faint sound of frying bacon, so I immediately powered down. Perhaps it wasn't up to that voltage. No harm done, anyhow.

My generator's a Leader LCG-396 of unknown vintage. New enough to be solid state. I have tried a few other sources, including the agile modulator that I use for in-home broadcasting, and at this stage nothing produces good color but the generator. Which could mean one of two things, I guess: [A] the generator's frequency is different than all the others, or [B] its signal is stronger. Regarding signal strength, tweaking the AGC control doesn't affect this problem.

I'll keep pokin' around.

Phil

not a new problem...
 

Over the years, ten percent of the operational CT-100 sets I know of have exhibited this problem. In these sets, changing the crystal has thus far been ineffective. While the gremlin(s) involved is(are) not yet fully exposed, the IF strip is suspect.

Since poor tube-socket connections can drastically change the signal level from the video detector, I speculate that same type of anomaly could cause a tilt in the IF response that could result in a loss of chroma sync.

Here's what I did for the signal level problem: used a bottle of DetoxIT D100L and some nylon cleaning brushes (also gotten from Craig) to SCOUR each tube socket connector.

Since the loss of OTA NTSC color, I nearly exclusively jeep the signal and bypass any IF problems. But, during the final years of NTSC, I didn't again experience the chroma sync problem.

I'm surprised the crystal comes in that can, since the RCAs from slightly later used the tube-envelope-with-a-crystal construction. Can't beat that awesome '54 date code, however.

I'll give those tubes & sockets another good cleaning. Like a two-year old's face, there no such thing as too clean!

Perhaps something's off in the front end. It's notable that the fine tuning point for best color bars and best DVD (or whatever) image are not the same. When I switch from generator to DVD player, I don't even get a picture until I turn the fine tuner somewhat.

Saying "best" tuning point for color bars sounds more precise than it is. One color or another will change as you move the fine tuner slightly, so I go for the best compromise (largest number of colors closest to ideal). Magenta is usually the hardest to get close. Perhaps there's a more scientific way to tell when the fine tuning is set to the right frequency . . . ?

Phil

Apparently, the "scientific way" to adjust tint is done by using only the blue gun and adjusting to equalize the blue bars.

I should clean house more often. I was rummaging through junk boxes and found these:

http://antiqueradio.org/art/RCACT-10...orCrystals.jpg

The cases are identical to the original, although the legs are a little thinner and closer together. The original has the codes 1107330 -1 4-54. These are stamped ED and have codes 1107863 -3 3-66 and 1107863 -1 4-77. If the last three digits are date codes, then maybe I have one from each decade.

I'll bend/thicken the legs on one of them and try it out.

I'm going to build the video preamp described in the 1956 RCA Broadcast News article so that I can bypass the front end. If the problem disappears, that tells us it was located upstream, I guess.

I also ordered some 100% DeOxit and leetle brushes to see whether cleaning the front-end sockets helps.

Phil Nelson

I got a new NTE358 crystal and cleaned all sockets the Pete way. Cleaned the tuner, too, while I was at it.

The original crystal was certainly off frequency, judging by what happens when you swap crystals without changing anything else. Assuming the new one is correct, the other old crystals that I found are also off by varying extents.

I redid the color AFC alignment with new crystal in place. The picture is strong and noticeably more stable than before. I think the cleaning was well worth the effort. We still have evil color bands, though.

http://antiqueradio.org/art/temp/RCA...olorAFCBad.jpg

I turned contrast & brightness way down on this one to show how stable and well defined the color bands are.

http://antiqueradio.org/art/temp/RCA...lorAFCBad2.jpg

Maybe I'm messing up somewhere in the color AFC procedure. The darned thing feels like it's so close to locking . . . .

Phil Nelson

Did you get the one I sent you?

There are 10 (maybe 12 with vertical retrace) color bands, meaning the oscillator frequency is off by 600 -720 Hz. So either the oscillator frequency is tuned this far off and the AFC can't pull it in, or there is something wrong with the phase detector [edit - or the reactance tube circuit] that is forcing it off to one side.

I did, thanks. I was able to find a new one after all, so I can return this one to you.

Regards,

Phil

Is there a chance to tune or detune the reactance control until the color bars are in sync?

If I needed it, I wouldn't have sent it to you. Go ahead and keep it.

Phil,

Wondering what happens when the color AFC is aligned using the DVD/Dorothy signal as the input...

Pete

You can access the top of the reactance transformer, 2T124 in the RCA manual ( http://antiqueradio.org/RCACT-100Tel...Service_Manual ). Is this what you're referring to? That adjuster is named A40 in step 37 of the Sams alignment instructions, http://antiqueradio.org/art/temp/RCA...structions.jpg .

Turning that control while watching the screen, I can change the number of bars but not eliminate them.

http://antiqueradio.org/art/temp/RCA...olorAFCBad.jpg

I wonder if the frequency is too far off to bring into locking range by that means . . . .

Phil

I recently made a test pattern DVD, so here are color bars from that DVD. I didn't change anything else since the previous photo except to switch the channel and adjust fine tuning a bit.

http://antiqueradio.org/art/temp/RCA...rAFCBadDVD.jpg

The generator input and DVD input seem to give roughly the same result. I may as well use the DVD on the next go-round, though.

Phil

Phil, that adjustment should bring the osc. into sync. See if it will lock in solid, or if it still has 'weak' sync. Bill(oc)

I'm not entirely sure what you mean by weak sync, but I can get it to lock on a set of horizontal color bands. They don't roll vertically. Moving that adjuster in one direction makes more bands. Moving it in the other direction makes fewer bands. In between the stable points, the bands roll. Continuing in the fewer-bands direction, the adjuster runs out of travel before you reach the Good Place.

Maybe something fishy upstream . . . ?

Phil

Phil, what does it do with the original crystal in place?

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.

http://antiqueradio.org/art/temp/RCA...nalCrystal.jpg

Colors aren't perfect, but we're back in the game.

I'm not sure what possessed me to try the original crystal, since I was so convinced it was bad. Couldn't think of anything else to try, maybe.

I should quit tormenting this poor old thing and just watch a movie for a change :)

Phil

In the first post on this thread the color bars from the generator looked fine but the DVD exhibited off-frequency color frequency of perhaps 120 Hz... Is Dorothy looking good now?
jr

Dorothy's back, too.

http://antiqueradio.org/art/temp/RCA...lCrystalOz.jpg

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

:DNo 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)

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.

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.

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.

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

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