TV Malfunction?

Originally I posted this in the wrong place, hopefully you guys can help me out with this.

I have an old TV (JCPenny RCA made in November of 1983) and I love it, except for one little flaw. Whenever there is any signifigant amount of the color white on the screen the TV makes a humming feedback static type of noise. What is this? Anyone have any idea? Id really like to fix this, since the vintage TV matches my stack and they are getting harder to find in such good condition. Thanks!

[Radiophile2001]

Hi, it may help if you could answer some of these questions:

Does the humming almost disappear when the volume is turned up decently?
Does it only appear when lettering is flashed on the screen?
Is it hooked up to an external cable box?

thanks

I can answer those. Its not hooked up to an external cable box, I hook the cable up to it directly. The noise happens most frequently though when I am watching a DVD or playing xbox on it. I am using an adapter for the Xbox and I have tried switching the adapters out and it doesnt really fix the problem. I havent noticed a change when the volume is a different levels, but the TV does usually stay at a low volume. It also doesnt only appear when letters are flashed on the screen, but it appears then too. Basically its when either large amounts of white appear on screen (like the intro to Halo 2 or when I am watching a movie where the set walls are painted a white or something in the same kind of family) or when the movie has lots of lighting. For example, the first nearly 20 minutes of Almost Famous are impossible to watch because its so brightly lit, and I can barely hear anything.

I am not electronically savvy. This TV has about 1000 knobs, and I am hoping something is adjusted wrong. Basically if you feel like it can't possibly be (blank) problem because only an idiot wouldnt have noticed that, you can safely assume I didnt notice it.

[zenith2134]

All i know is that a totally white raster would demand the most High voltage due to the fact that all 3 guns are working in unison.
I've worked on sets that did this and it was one of two things:
1. flyback transformer core vibration due to increased stress or malfunction,
2. Weak power supply i.e. a bad cap somewhere

Don;t work on any part of the supply circuit unless you're qualified though, as you may get zapped badly.

P.S. Try adjusting the knob labeled 'AGC' or RF AGC , if the buzz is in the audio itself, may just be the video is peaking and spilling into the audio

[colortrakker]

Sounds like a classic case of signal overload. The video signal going into the TV is too strong and is spilling into the audio. Does the cable buzz too or is it only the Xbox and DVD? Do you run the DVD and Xbox through a switchbox? How's the cable signal? Not knowing exactly how you're connected, I'd begin by recommending an inline attenuator like this one to bring the signal down to a more tolerable level for the TV. If your DVD and Xbox run through a switcher and your cable is fine, put the attenuator on the cable going from switcher to TV and see if that doesn't solve the problem.

[jstout66]

sounds like a video overload to me as well. My Chromacolor 2 does it and it drives me nuts. On some sets you could turn down the AGC a bit. Don't know if the RCA with the problem has an AGC control.

[andy]

It could also be caused by IF misalignment, or even fine tuning, or auto fine tuning. If it's only happening when you use the RF modulator, try another RF modulator. I'm willing to bet that some of those cheap RF modulators don't do a very good job. Isn't the discriminator coil on those RCAs located right next to the audio IC? A simple adjustment of that might be all that's needed.

What ever you do, don't adjust anything until you know what you're doing. Blindly playing with the alignment WILL render the TV useless.

[wa2ise]

An analog TV channel's RF level dips to a minimum during the time peak white is transmitted. If the biasing or alignment in the IF circuits is not optimium, this RF signal level could go to zero. And modern analog TV sets use the "intercarrier" sound system, which needs some amount of picture carrier to function correctly. If the picture carrier disappears for short periods of time (fractions of a second) the detected sound subcarreir disappears and the FM subcarreir detector sees "holes" in the signal and will output a buzz when these "holes" happen.

I don't suppose the TV set has baseband audio video inputs. But if it does, use them for the DVD or xbox.

[andy]

Macrovision which is output by DVD players makes matters worse. It inserts whiter than white signals in the VBI which push the limits of even a properly aligned TV.

Theres something in the back of this TV, i dont know what a baseband input is...I wish I could take a photo for you, but the cameras batteries are dead and I am out of remotes to take it from

But heres what I see...in a nutshell

This whole section is called "input"

I see a video 1 with two jacks and a line connecting them that says "bridged" and then theres a switch that says "term" on one side and "bridged" on the other and a knob that says "level"

I see video 2 with one jack and a knob that says level

I see audio 1, with 4 jacks, two right, two left both bridged and a switch that gives you a stereo/mono choice

I see audio 2, two jacks, one right one left

I also see a section called "outputs" one jack for video, one jack for audio, two jacks for "audio to hi-fi"(one right and one left) and two BIG jacks that say EXT SPEAKERS

So...what the hell is all that? If I am supposed to hook the DVD player to that does anyone know how? I dont have the original remote. Listen, thanks guys for taking time out of your days to help me out. I am a total electronics newbie, but I am so fasinated with this stuff, and you guys being helpful really means alot to me. Thanks.

[wa2ise]

Originally Posted by ArcticBlue

Theres something in the back of this TV, i dont know what a baseband input is...I wish I could take a photo for you, but the cameras batteries are dead and I am out of remotes to take it from

But heres what I see...in a nutshell

This whole section is called "input"

I see a video 1 with two jacks and a line connecting them that says "bridged" and then theres a switch that says "term" on one side and "bridged" on the other and a knob that says "level"

The DVD player video (yellow jack) would connect to here. Set the switch to "term". Set the "level" near its upper limit, usually all the way clockwise (like a volume control). using the remote (if you had one, or a universal replacement) or the channel keys on the TV set itself to select channel "91" to get the set to accept the video and audio fed here. "92" selects video 2. The on screen display may say "A1" or "A2".

I see video 2 with one jack and a knob that says level

feed the xbox video to this

I see audio 1, with 4 jacks, two right, two left both bridged and a switch that gives you a stereo/mono choice

The DVD left and right audio goes here. set the switch to "stereo"

I see audio 2, two jacks, one right one left

feed the xbox audio here

I also see a section called "outputs" one jack for video, one jack for audio, two jacks for "audio to hi-fi"(one right and one left) and two BIG jacks that say EXT SPEAKERS

So...what the hell is all that? If I am supposed to hook the DVD player to that does anyone know how? I dont have the original remote. Listen, thanks guys for taking time out of your days to help me out. I am a total electronics newbie, but I am so fasinated with this stuff, and you guys being helpful really means alot to me. Thanks.

This TV set sounds like the RCA CTC121. I have one here. Be aware that the level controls for the video might get dirty, so wiggle them a little to clear a bad wiper contact inside the control if you don't seem to get a picture.

Thank you SO MUCH! And yes thats my TV. You guys are the best! I had tried hooking up the DVD player and xbox back there before, but couldnt figure out how to get the TV to feed in the video, so just assumed that it simply didnt work. Thanks again!

[Radiophile2001]

On one of my tube sets, if the volume is turned all the way down or is set low, I can hear that buzzing sound. It can be worse with white lettering on the screen. If the video is off-tuned to distortion, but the audio signal is still tuned in (ie on a UHF station), the buzz goes away. It seems worse with more white on the screen, but not that much worse. Is this situation adjustable with the AGC control?

Thanks

Originally Posted by jstout66

sounds like a video overload to me as well. My Chromacolor 2 does it and it drives me nuts. On some sets you could turn down the AGC a bit. Don't know if the RCA with the problem has an AGC control.