Chromacolor II Color Screen Shifting

[Jon1967us]

Here you can see, depending on scene, and with color turned all the way down, color shifting. Can’t figure out what’s causing this. The module contacts on the video board are sound, all transistors test ok and no cold solder joints that i can find.

https://youtu.be/2W6-IvIy9Lk

[zeno]

If the outputs on the 9-89 board are plug ins solder them in.

G-2 controls got bad spots but IIRC they also gave retrace lines.

If the ACC control on the 9-86 is set wrong it may let some color through.

Monitor the K, G-1 & G-2 voltages of CRT & look for changes. Best to
use a test pattern & an analog meter.
BTW model & chassis ##'s ?

73 Zeno
LFOD !

[Jon1967us]

Originally Posted by zeno

if the outputs on the 9-89 board are plug ins solder them in.

G-2 controls got bad spots but iirc they also gave retrace lines.

If the acc control on the 9-86 is set wrong it may let some color through.

Monitor the k, g-1 & g-2 voltages of crt & look for changes. Best to
use a test pattern & an analog meter.
Btw model & chassis ##'s ?

73 zeno
Lfod !

19ec45

[zeno]

If you havnt check the safety caps. Under run 401 will have 4 or 5
22-5001 caps. If white change them. They are scattered around
the HV & hoz out and on the sub chassis.
Run 401 & higher has one 4-lead cap under the hoz out
heat sink. If white change it. Orange Sprague caps are GOOD.

[mrjukebox160]

I have seen this before. You have a weak gun/s on the CRT. When you have a bright seen, the CRT heats a bit more from the current draw and emission comes up. On a darker seen it drops. The "clean and balance" or lowest setting on a CRT rejuvenator will correct it.

[Jon1967us]

Originally Posted by mrjukebox160

I have seen this before. You have a weak gun/s on the CRT. When you have a bright seen, the CRT heats a bit more from the current draw and emission comes up. On a darker seen it drops. The "clean and balance" or lowest setting on a CRT rejuvenator will correct it.

Sounds interesting, but all of my guns test very good on the Sencore CR-70. Cut off is good too.

[Jon1967us]

Something noteworthy. I can set the greyscale just fine when there’s no video content on a unoccupied channel. I get grey snow with even distributed color sparkles. Only when I’m on a channel with a signal does this occur.

[DavGoodlin]

Thanks for posting a great symptom video. I saw many of these in Best Western Motels and Holiday Inns when on family vacations in the 70s

My $.02 = A cap somewhere on the supply to video amps, just a guess considering its a very odd symptom, usually those are found on a Zenith.

Video balanced to drive 3 cathodes (K) and demodulated colors drive each G2 from the 9-89. Looking at G2's and K's on a scope will show a changing video or demodulated color, which may not be the issue. It is the DC baselines of K or G2 drifting along with CRT beam current.

In the video, its pretty apparent the Scully scene has a "larger bright area" that could:

1. Trigger a gradual increase in B+ to the green G1 - monitor per Zeno's post
2. Be spark gap in crt socket choked with dust, considering only one color is wonky.
3. Be drop in voltage at green cathode, heater-cathode leakage, heater line is tied to B+ via resistor - monitor per Zeno's post, changes here would be obvious.
4. triggered by HV tied into the brightness limiter, may be a buffer cap ?

Ill check my Zenith notes and TAB service manual volume III?, there may be something circled on a schemo, I have loose leaf schematics pulled from service binders that were tossed.

[Jon1967us]

DavGoodlin;3241546]Thanks for posting a great symptom video. I saw many of these in Best Western Motels and Holiday Inns when on family vacations in the 70s…

This one could very well be a hotel or institutional set. It has a built in Coax in (75ohm?) near the antenna terminals. Also has a “#6” etched into the plastic cabinet.

I think I will take a deep look into the luminance module, especially the limiter, and will check out the other suggestions. Whats also Interesting is that when the set has a cold start (filaments not under instant on voltage) the pic is entirely green and takes a bit for other colors to come in. Something needs to warm up and i suspect a crt or socket problem. Spark gap a great idea to investigate.

What’s the best way to clean a spark gap?

[DavGoodlin]

Originally Posted by Jon1967us

What’s the best way to clean a spark gap?

Use any electronic connector cleaner. Just get the plastic cover off the CRT socket and try tha.

Do measure the K-G1-G2 voltages and post them. Make note of changes during warm up scene changes, etc.

[zeno]

its probably a hotel set. Even looks like one. Usually there is a tag on the back
that says " no labor warranty". Model number will also reflect it MOST
of the time. IIRC E & F line sets only had coax on varactor tuner models.
Since its an E line it would have come with plug in IC's & transistors.
Pull & clean the 4 transistors on the 9-89. Do the same with the 2 IC's
on the 9-86. You can do a little pushing to see if it acts up.
Since it seems to only happen with signal I bet its on the 9-86.

73 Zeno

[Jon1967us]

Originally Posted by DavGoodlin

Use any electronic connector cleaner. Just get the plastic cover off the CRT socket and try tha.

Do measure the K-G1-G2 voltages and post them. Make note of changes during warm up scene changes, etc.

Voltage measurements: all cathodes, as specified on schematic - from 145-155v. When brightness and contrast to a lesser degree, were turned down, K voltages go up and screen was tinted green, even if that G1 is turned all the way down.

Got as far as measuring Green G1 and only got 33v. Noticed the pin was bent, and with contact wiggled loosely. The pin indeed was broken internally and bent. Bending the pin straight and inserting as far as possible seems to have made contact internally with the G1 lead.

The green cast seems to have been removed by this action, now that I can put appropriate voltage on green G1. Color doesn't shift around. Will monitor for now and see how things go.

In video capture I show greyscale and color saturation. I do vary the tint a little at one point to show the range. https://www.youtube.com/watch?v=oGT3...l=Silvertone58

[old_tv_nut]

Wow - floating G1 - great diagnosis to have in the back of your mind if you see this symptom.