I'm working on an Admiral 20A1 chassis and I can't get both sound and video on a given channel. Adjusting the tuner oscillator slugs will get one but not the other. I connected my sweep generator/marker (B&K 415 sweeping on channel 4 with sound and pic markers set) and got what looks like a typical video response except it occupies only about half of the proper bandwith of 5 MHz or so. Adjusting the oscillator slug pushes the response one way or another and visually explains why I can get sound but no video and vice versa. What would cause this video response? I've checked all relevant voltages in the video IF strip and all seems OK. I don't think it's the tuner because I've connected another one temporarily with the same results.

:I'm working on an Admiral 20A1 chassis and I can't get both sound and video on a given channel. Adjusting the tuner oscillator slugs will get one but not the other. I connected my sweep generator/marker (B&K 415 sweeping on channel 4 with sound and pic markers set) and got what looks like a typical video response except it occupies only about half of the proper bandwith of 5 MHz or so. Adjusting the oscillator slug pushes the response one way or another and visually explains why I can get sound but no video and vice versa. What would cause this video response? I've checked all relevant voltages in the video IF strip and all seems OK. I don't think it's the tuner because I've connected another one temporarily with the same results.

Check the resistors across the 1st video IF transformer (12K) and the 2nd (10K).

The first plate resistor was 12k and one of the production changes indicates an 8.2k resistor was used in later models to improve IF performance. I went with an 8.2k plate resistor and it improved the situation slightly but the sound is still too far away from the picture. Sad because it's the best looking video response I have seen (looks like the textbook response) but it just won't occupy the intended bandwidth. It might be time to look for a new video strip for this set.

:The first plate resistor was 12k and one of the production changes indicates an 8.2k resistor was used in later models to improve IF performance. I went with an 8.2k plate resistor and it improved the situation slightly but the sound is still too far away from the picture. Sad because it's the best looking video response I have seen (looks like the textbook response) but it just won't occupy the intended bandwidth. It might be time to look for a new video strip for this set.

Might be a bad IF transformer, but I don't think so as the waveform is good; I would expect a lousy waveform with a shorted/open winding.

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:Might be a bad IF transformer, but I don't think so as the waveform is good; I would expect a lousy waveform with a shorted/open winding.

I don't know if this is a clue or not. On a given channel, when I adjust the fine tuning to get the best picture, I also tune in a "buzz". The buzz disappears with slight adjustment either way. I sure wish my sound was where the buzz is!

The audio is still there but it takes approximately 1/2 turn of the oscillator screw. But by then, the picture is toast.

Hi

This is a very early TV. The problem was fairly common in the 1950's. Could be alignment but you might also try less input signal. A strong signal might overpower the TV causing video buzz in audio.

Norm

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::Might be a bad IF transformer, but I don't think so as the waveform is good; I would expect a lousy waveform with a shorted/open winding.
:
:I don't know if this is a clue or not. On a given channel, when I adjust the fine tuning to get the best picture, I also tune in a "buzz". The buzz disappears with slight adjustment either way. I sure wish my sound was where the buzz is!
:
:The audio is still there but it takes approximately 1/2 turn of the oscillator screw. But by then, the picture is toast.

:I'm working on an Admiral 20A1 chassis and I can't get both sound and video on a given channel. Adjusting the tuner oscillator slugs will get one but not the other. I connected my sweep generator/marker (B&K 415 sweeping on channel 4 with sound and pic markers set) and got what looks like a typical video response except it occupies only about half of the proper bandwith of 5 MHz or so. Adjusting the oscillator slug pushes the response one way or another and visually explains why I can get sound but no video and vice versa. What would cause this video response? I've checked all relevant voltages in the video IF strip and all seems OK. I don't think it's the tuner because I've connected another one temporarily with the same results.

Rene:
How about looking at the audio IF? Maybe it's not 4.5 mHz anymore???

Lewis

:Rene:
:How about looking at the audio IF? Maybe it's not 4.5 mHz anymore???
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:Lewis
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:Hi Lewis,
I think you might be referring to a set with intercarrier sound. This set has two IF's with the sound IF at 21.25 and the video at 25.75. I've aligned the sound and video IF circuits with an accurate Tektronics constant amplitude signal generator.

After doing some reading on stagger-tuned video amplifiers, I'm starting to think that the amplifier tuned at the low end (22 MHz) is the one that is way off...hopefully something simple like a resistor but likely it's a bad transformer.
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::Rene:
::How about looking at the audio IF? Maybe it's not 4.5 mHz anymore???
::
::Lewis
::
::Hi Lewis,
:I think you might be referring to a set with intercarrier sound

Yes, that's exactly what I'm thinking about....well, back to the thinking cap.

Lewis