Quote:
Originally Posted by kbmuri
I'll try reducing the generator's amplitude Friday.
One thing we know, though, is that the audio from the generator doesn't get through at the desired 65.75 MHz, regardless of its amplitude. Finally, this agrees with the fact that there's no TV-Signal audio either (assuming it's at 65.75 MHz too). Something I can grasp for a change.
Assuming the generator is AM only (I believe my 'scope bears this out), then the "lull" at 63.65 MHz is probably the dead-center point you described in post#6? If so, then is the TV mistakenly looking at 63.65 MHz for audio?
Assuming the zero-beat of the video is centered in the "black-screen" sweep, then the video and audio are only 2.85MHz apart. More likely, if the zero-beat is in fact at 61.25, then the spread is only 2.4 MHz. Not 4.5MHz.
If the TV is looking at 63.65MHz for audio, what practical steps do I take to move that up to 65.75?
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If I recall correctly, this TV set does not use the intercarrier system (using a sound IF at 4.5MHz) but has an independent sound IF normally set 4.5Mhz away from the video IF. But even if this offset is off frequency, you should still be able to play with the TV's fine tuning knob to find the sound carrier (even if the video becomes unwatchable). I assume that the fine tuning can move the tuner's local oscillator by 6 MHz.
If the sound IF is off frequency, you can "walk" it up (or down) in frequency by adjusting the signal generator first dead on where the IF is set now, then adjust the generator so it's slightly off in the needed direction. Then tweak the IF transformers to make it dead on again. Repeat multiple times.