Help! Color dropping in and out on 1978 Zenith Chromacolor II television

[LucidusAtra]

Hey everyone! Is anyone out here experienced with early color TVs?

I was recently given an old Zenith Chromacolor II television, and have been playing around with it. It's been great! There's no coaxial input, only twin-lead, so I'm using one of those twin-lead to coaxial adapters. I have a VCR with a coaxial output set up, and it's working as an RCA input. However, I'm finding that sometimes, the color drops out. At first I was worried that this meant the cathode ray was beginning to fail, but I don't think that's the issue here, because adjusting the fine tuner knob brings the color back immediately. So my current working theory is that something is affecting the TV's fine tuning. Either the channel that the TV is tuned to is being pushed slightly off, or the VCR, which is set to send its signal to channel 3, is actually sending its signal somewhere between channels 3 and 4, and the channel that the signal is being sent to is fluctuating for some reason. I've tried three different twin-lead to coaxial adapters, so I don't think it's due to a faulty adapter.

Does anyone have any theories about what might be causing these fluctuations? Having to get up and adjust the fine tuning knob every few minutes is pretty annoying. I've got four game consoles -- an Atari 2600, a Nintendo 64, a PlayStation 1, and a Sega Genesis, hooked up to the TV. The Atari, PS1, and Genesis are all connected through VCR's coaxial input, while the Nintendo 64 and an ATSC tuner with an antenna are hooked up to an RCA switchbox, which is connected to one of the VCR's RCA inputs. The VCR has a second RCA input, to which I've connected a DVD player. Maybe there's electrical interference coming from one of my devices? The VCR, DVD player, ATSC tuner, and antenna are all sitting on top of the TV, next to the RCA switchbox, pretty close to the twin-lead input

Any help would be appreciated!

 

[Bluejets]

Sounds a bit like signal strength loss.

 

[LucidusAtra]

Sounds a bit like signal strength loss.

Hmmm... What can I do to strengthen the signal? This is my first time ever working with a twin-lead input, so I'm an absolute novice here.

 

[Bluejets]

Depends just how much signal you have now. Usual approach is to have sufficient signal from the antenna.
From your description it sounds like you are using just a set top antenna so might be a good move to get an external antenna sufficient to suit your particular area.
You will be getting losses at your VCR as well.

 

[LucidusAtra]

Oh, you're talking about TV broadcast signal. Hmm... I don't think that's it. That wouldn't account for the color going out on my video game consoles, which are connected directly to the TV, and have nothing to do with the antenna. The ATSC tuner only picks up digital signals (analog television broadcasting ended in the US in 2009), so the strength of the signal shouldn't affect the picture quality until the signal is so weak that you can't get a picture at all.

Wiggling the regular channel switching dial without turning it seems to make the.color drop out. Maybe it's as simple as a loose dial?

 

[Bluejets]

Mmm..ok.
But signal from an av input doesn't come through the tv turner so a bit confusing there.
Edit...so assuming you are using some form of rf box to retransmit to tv?

 

[LucidusAtra]

The TV tuner is one of several devices I have connected to the TV through the VCR's AV input. I'm using one of these (https://www.frys.com/product/164594...Q-fem224JAVW-0IvU_uGE8z2Z9nmya_hoCmaAQAvD_BwE) to connect the VCR, which only has a coaxial output, to the TV's twin-lead input. The color drops in and out when I use any of my devices.

 

[Bluejets]

Device shown is a 300 to 75 ohm adaptor, no problem there.
You mentioned some coming and going of signal when you wriggle some section. Probably investigate that area a little further.

 

[kellys_eye]

Google 'NTSC color burst signal'

 

[73's de Edd]

Sir LucidusAtra . . . . .

Confirm if this is being the signal path.
VCR comes into the Zenith thru the mentioned 300/75 transformer *** and you then either can play a tape or have a Digital converter box coming into the VCR for watching off air digital TV . . . .or . . . . using RCA video inputs into the VCR will accept composite video.
Is this Zenith having the old click / click mechanical tuner and a fine tuning knob just BEHIND the channel change knob.
Or . . .
Is it using electronic tuning where you tune in trim pots for each VHF channel and a very limited number of UHF channels ?

*** INFO . . .
I THINK that there are sets of 300 ohm VHF/ UHF antenna input terminals . . .BUT . . .if you will look, there is being a VISIBLE black loop of black 75 ohm cable that is plugging into that ant terminal block. Additionally, there is a large brass hollow crimped sleeve / collar around one end of the coax that precludes any of it being pushed into the tv case.
The opposite end of that coax loop has a female F59 cable that plugs into the ant terminal block. If you will pull straight out on that, it will unplug. That 75 ohm coax stub is then being the normally utilized VHF 75 ohm input into the tuner . . . .thereby eliminating the dual losses presently incurred by both your redundant 300 / 75 transformer and the 300 ohm terminal block.

Continuing . . . .

I believe that the II has a YELLOW rectangular push button marked as CHROMACOLOR.
If it is pushed IN the set goes to a pre set color and hue color adjustments AND engages the Automatic Fine Tuning, associated with the tuner .
If the button is left to pop OUT you then have to manually adjust the color and hue color adjustments . . . if so needed.
BUT the AFT is now disabled and relying upon you to manually set the fine tuning for best pic and color.
Try running the set with the II pushbutton out and set the fine tuning for good color and watch to see if it runs for longer that you had ever experienced before.
Also if that is a mechanical tuner, dirty contacts could be the cause your tuner drift or pop off of color. Sharply side tap the tuner knob to see if it wants to intermittently lose the station / color.
with no corrective AFT now being present, it should be readily apparent.

Until you come back . . .with ur findings . . . I still wonder if you lose color on all input categories . . . . .with the strong 1000 uv RF coming in via the VCR modulator on 3 or 4 . . . not being expected to give a problem . . . when playing a tape..
If this above is not the fault source , there are two plug in chroma modules, yet to consider..

Thaaaaaaassit . . .

73's de Edd
.....

 

[LucidusAtra]

Hey 73's de Edd! Thanks for the reply!

Yeah, you have the signal flow right. The VCR outputs to the 300/75 transformer, which outputs to the TV. I have my digital converter box coming into a composite video switchbox with four inputs, and the switchbox outputs to the VCR. I also have a few video game consoles coming into the VCR through the VCR's coaxial input.

There's one of the old fashioned click mechanical tuners, with a smaller fine tuning knob right to the left of it. You have to push the fine tuning knob in to manually adjust the fine tuning, and it seems to have a spring behind it, so that when you let go, it pops back out, making it harder to accidentally adjust the fine tuning setting you've settled on. However, even after I've adjusted the fine tuning and allowed the fine tuning knob to pop back out, the color will still drop out a few minutes later. There's a switch labeled AFC, but it doesn't seem to have any noticeable affect on anything.

There's no yellow "Chromacolor" button, but there's a circular push button next to the volume that's labeled "Color Sentry." This does seem to change to a set of preset color settings, but it doesn't stop the color from dropping out.

I've found that wiggling/touching the big click mechanical tuner knob makes the color drop in and out, and then fine tuning brings it back temporarily. You mentioned that dirty contacts could be the cause of the tuner drift? I think that's EXACTLY what my problem is! Is there a proper way to get in there and clean those contacts? I don't want to break anything.

 

[LucidusAtra]

Oh, I forgot to mention, the color goes out no matter what device I'm using, even if I'm playing a tape. Even if I'm not playing a tape at all, the VCR's blue background screen will turn black.

 

[73's de Edd]

Sir LucidusAtra . . . . .


Pending further clarification . . . .

With your description of the push in to activate aspect of the fine tuning knob, and the separate AFT sw and if your unit looks like this, you have an electronics tuner utilized there and its not subject to 144+ huner contacts developing intermittency.
Also your unit could also be a remote control model ?

Also what is the picture tube size ?
You need to initially try what I said in respect to see if the fine tuning is not affecting the unit and causing this problem.
Initially slide the AFT switch to its OFF position and then push in and rotate the white knob to he right untill you loose your pic due to tuning into the sound frequency and the resultant wig wag lines crosshatch. Rotate back until the pic just clears of that lines trashiness, and that will then be your optimum fine tuning setting.
Then leave the AFT OFF and see if the set operates any better, relevant to color drop out..
If not its, back off time and get ready to find the 2 chroma related plug in modules and initially clean their 15 or so contacts each..

TUNER FRONTAL CLOSE UP . . . .



73's de Edd
.....