CT-100 color sync issue?

[Phil Nelson]

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:



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:



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

[jr_tech]

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

[ctc17]

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.

[old_tv_nut]

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.

[miniman82]

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.

[freakaftr8]

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

[Phil Nelson]

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.



Phil

[miniman82]

You have PM.

[ohohyodafarted]

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.

[ctc17]

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.

[Phil Nelson]

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

[Pete Deksnis]

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.

[leadlike]

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.

[Phil Nelson]

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

[colorfixer]

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