Screaming Picture Tube??? - Videokarma.org TV - Video

#1 03-13-2006, 08:27 PM

I got a 12" B/W Zenith portable. Looks from the 50's or 60's. No picture. Loud squealing noise that seems to be coming from the pciture tube. I hear it even with the volume down. When I turn up the volume I hear it through the speaker (picking up the frequency I guess) and hum through the speaker when I turn it up more. But when I turn the volume down all the way this loud screaming noise remains. And I mean it is LOUD! I have never had anything like this happen and am kind of afraid to work on it now. Any help would be much appreciated. Thanks in advance!

Sandy G · #2 03-13-2006, 08:38 PM

Take It Out 'n' Shoot It !! It's Haunted !!.....

bgadow · #3 03-13-2006, 10:37 PM

I would suspect the horizontal frequency is way off (caused by bad caps or resistors?) and would start with that. Some of the sound could be eminating from the yoke?

kx250rider · #4 03-14-2006, 12:35 AM

With good hope, I bet all that's wrong is that the anode lead is loose, and is stuck on by the suction cup only! Has happened to me many many times. (if not familiar), beware that when you go to check it, you can get a 13,000 volt shock if you don't ground it out first even if the TV has been unplugged... Take a thin long screwdriver, attach a wire from the screwdriver to the metal TV chassis, then stick the screwdriver under the suction cup to ground it out. Obviously use a plastic-handle screwdriver.

No promises, but hopefully that's it! If not, then Bryan also has an excellent guess with the horizontal freq being way off. That can come into the sound if it's that far off, and it will make a high pitch noise from the yoke.

THIRD possibility is a broken or cracked picture tube. If you see purple flashing in the neck of the tube, then you have a broken picture tube, hopefully not though!

Charles

Carmine · #5 03-14-2006, 07:38 AM

How about the windings in the flyback (oscillating)? If I were to fault anything as "typical Zenith", this would be it, although I've always seen it on color sets.

BTW, cool looking set in your Avatar!

#6 03-19-2006, 12:24 PM

I'll have to look into this more. When I was working on my Hoffman TV I accidentally touched the anode with my left hand, and the chassis right my right. I heard a psst and felt a shock across my neck and arms! Well I don't want that to happen again! I'll have to bypass the interlock somehow in order to check for a bad CRT. Like you said, KHTV, hopefully not, or I will have to just sell it for parts. Of course, once I get it wired that way, I'll have to check for the other noted situations as well, like the yoke and flyback. But hopefully it's as simple as the anode cap.

I brought in a large video monitor today that has a similar problem. However the CRT seems to work normal, although the input VHF signal is not getting through. Perhaps this problem or more complex. With the Zenith, hopefully it's just some bad condensers or resistors.

Whirled One · #7 03-19-2006, 05:08 PM

You didn't mention any odd smells, but if it's a screeching sound that sort of varies in volume, and you also smell ozone coming from the set, it's probably HV arcing. As Kaye-Halbert TV suggests, it might just be that the 2nd anode lead is loose. If that's not it, try operating the set in the dark with all of the room lights off and see if you can spot the location of the electrical arcs.

It could also be a way-off horizontal oscillator as others have suggested, but flyback squeal has a different/distinctive sound that should identify it.