Thoughts on chroma crystal ocsillator troubles

[Tubejunke]

How often do these things go bad? Just wondering if it's common or almost never for them to be a cause of color loss. I think it is a 3.57Mhz crystal. I slow started my 64 Zenith 5111 which was a couple of decades dormant and was pleased with a great color image.

It was interesting how the TV came to life as initially there was only black and white and then in sort of a spiral the color came in starting in the center and moving through the entire picture. That lasted a a couple of hours or so and the set went black and white again. None of the adjustments make a difference.

This was a while back and someone here sent me a replacement crystal that looks like a capacitor; like a large, thick ceramic disc dipped in blue plastic. It's some kind of modern sub that is supposed to work. Anyway, I hardly ever see posts or threads on these crystals and the role they play in loss of color. My bet is that the set has a bad cap (of course), but it would be nice if the crystal was the culprit.

[oldtvman]

On older sets it's not unusual to have bad capacitors. I would go after those first before I would condemn the crystal

[Phil Nelson]

I agree, capacitors are so much less reliable than a crystal, I'd suspect them before anything else. I have replaced bad electrolytic caps in equipment made as recently as the 1980s, and found MANY more bad caps (electrolytic and other types) in 1960s-era TVs.

When I had a color sync issue in my CT-100, I got my hands on some old-school crystals and tried substituting them. I eventually concluded the crystal was not the problem, and today it's running with its original crystal.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Don Lindsly]

The chrome oscillator crystals were very reliable. For your symptoms, I suggest replacing the burst amp, chroma oscillator, phase detector and going through the chroma AFC alignment. Clean the tube sockets and set the fine tuner. That will fix 90% of color osc troubles.

If the oscillator runs on frequency the crystal is OK.

Don

[old_coot88]

Originally Posted by Don Lindsly

If the oscillator runs on frequency the crystal is OK.

Don

This is true provided the tube is good. There's a quickie way to tell if the osc. tube might be borderline weak.. After the set's warmed up good and everything's in sync, shut the set off for around 5 - 7 seconds, and back on again. If the color comes on barber-poling and takes a while to lock in, the tube is borderline. And this is with a good crystal.

The same technique can be used to show up a borderline horiz osc tube, horiz output, or vert output tube.

[BigDavesTV]

More often caps, and/or tubes, especially sets with 5/ and 6GH8(A) tubes, especially RCA. Your Zenith may have a weak color osc. Tube, or cap, but also could be a dirty tube socket. I have not seen many osc. Crystals bad, but I recently had one bad in a Motorola TS 921 chassis, after checking tubes, connections and caps, was a bad crystal, now has color sync! :-) Good old Zenith, to fire up on slow start after several years!

[Tubejunke]

OK, lots of good information folks. Thanks! I think I will wait on messing with the crystal since it seems to be color sync related and that's not my problem. There is no color to sync.

Looking around in there I see several black paper capacitors that I am thinking might be a newer version of the older bumble bee caps that so notoriously fail. The drops may be OK. That remains to be seen. At least I have a good black and white picture which means a lot with a color set.

[oldtvman]

If this helps you any, you can buy cap checkers on ebay pretty cheap. It's a handy tool to have around if your restoring vintage electronics.

[Phil Nelson]

There were other plastic-coated paper caps, without stripes, that are just as unreliable as bumblebees. The pink caps in this photo are examples:



They can also be in black cylinders with printed values rather than stripes, etc.

Another type of plastic-coated paper cap is flat and rectangular, similar to this:



Some people call those "micamolds" after that company's name, but they were also made by Solar and other companies.

All of those caps use paper inside and they are just as bad as wax paper caps. No need to test them unless you are curious -- they are garbage inside, even if the plastic case is still shiny and new-looking.

I'd guess that in a 1964 set, "drop" type caps -- similar to orange drops, but they can be colored maroon, brown, blue, green, etc. -- are iffy. In my 1961 RCA CTC-11s, both sets worked, kinda, sort of, with the old "drops" in place, but they didn't work well until I replaced them. With all of the original drops in place, my 1958 CTC-7 showed a weak picture with bad vertical & horizontal sweep and little or no color.



The more maroon drops I replaced, the better it looked, until I got this:



If you want a cap checker, you must get one that can apply the cap's actual working voltage (i.e., don't rely on a modern handheld meter). Here's one that I use:



There are other brands & models; I also have an EICO 950B. Any vintage cap checker will need restoration, like a radio or TV of the same age. I use mine mainly to test mica caps. I don't test paper caps, for the same reason that I don't check the air pressure on a tire that's obviously flat. Maroon drops . . . maybe, although I can replace one in about the same time it takes to haul out a tester and check it.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[Fant]

When you do not have any color in the picture, turn the color killer control so that color killer is off. Color may come back because killer was set for a strong TV signal. With killer off you may see floating colors. This means the color oscillator is off frequency. Short the test point (grid of reactance tube) to ground and adjust frequency coil until colors stay still. If a color picture only has greenish hue, the 3.58 oscillator is dead. Try a new crystal or tube.

[Fant]

In the 1960's when I checked paper/wax condensers (caps), I used a 225 volt photoflash battery in series with a disconnected condenser and a Simpson 260 VOM. If there was any leakage volts, I replaced the condenser. We bought Sprague condensers ( black beauty and orange drop) 100 at a time and got an extra discount on them.

[Tubejunke]

Originally Posted by Phil Nelson

They can also be in black cylinders with printed values rather than stripes, etc.

If you want a cap checker, you must get one that can apply the cap's actual working voltage (i.e., don't rely on a modern handheld meter). Here's one that I use:

THAT is the cap checker I want! I love the vintage test equipment although one has to think whether they want their repair tools to need repair. That magic tuning eye takes the cake on that one. I will probably never find one of those.

Thanks for the rundown on how well some of these caps that are a bit newer are holding out. In older sets the old wax paper is a given to get out of circuit, but there are many stories of people having fairly well working and a bit newer color sets do well with the maroons and such. Again, I saw several black, plastic coated (probably Sprague) caps with yellow values printed that I wanted to get out along with a big blue electrolytic that I think is in one of the video circuits. After seeing your results I think I will take this a little further.

[Phil Nelson]

Cap checkers are simpler devices than TVs, so restoring them is usually straightforward. Here are articles about the Solar and EICO checkers.

http://antiqueradio.org/SolarCB-1-60...orAnalyzer.htm

http://antiqueradio.org/EICO950BBridge.htm

These items generally go cheap at swap meets.

Phil Nelson