Quote:
Originally Posted by bob91343
If indeed the set was designed to decode a stereo signal (you can't be sure unless there is a stereo switch), then the problem is in the decoder circuitry. Anything that old is pure analog, so you have to check for the pilot 19 kHz signal being detected and doubled (or synchronizing) to 38 kHz to achieve the L-R signal.
Maybe a simple alignment will make it work. Trace out the circuit and try to guess which alignments you need to tweak. Don't adjust anything unless you know what you are doing.
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Well it is a stereo set. There is a stereo light and if you look at the picture closely you will see a stereo/mono switch.
The IC chip inside is a true stereo FM decoder.
So how do I go about tracing the 19Kc pilot? I have the IC chip pinouts and there is a filter to remove the pilot, and another to feed in the composite signal, and yet another to go into some kind of PLL setup.
I did peak a few of the FM detector coil boxes but I put them right back after trying it. Only difference that made was with reception anyways.
I don't understand the circuit that well. Reading the PDF on the chip doesn't give me much info...
http://pdf1.alldatasheet.com/datashe...C/AN7420N.html
I have a scope if need be used. Usually with something this cheap I could care less to fix it but I need a project lol.