Hi Guys,
This is my first post here. I am a novice hobbyist just enjoying electronics and trying to learn a few bits and pieces along the way. I got stuck with my latest project and thought I would seek some help here.
I have a Sony XR-CA400 with what seems to be a faulty TUX-A20 tuner unit. There's no audio at all when in radio mode, although both tape and cd works great.
A bit more detail: The voltages to the A20 are ok (+8 and +5). I don't have means to decode SDA and SCL but they show up on the scope. What is missing is the MPX that seems to "hold" the actual audio. Also no RDS.
This makes sense because the radio does not find anything when seeking. It seems to be "missing" the antenna. I've traced the path of the antenna a fair bit on the A20 board but I do not understand how this piece of the circuit works, making it a bit difficult. Same thing for both FM and AM. The A20 is not explained in the service manual for the radio and there's no schematics for it.
I know this is a long shot but have anyone a clue of what could be wrong? Otherwise, where can I get I new A20 board? Or the schematics for it?
Here is a link to the Service manual:
http://elektrotanya.com/sony_xr-ca400,ca420x.pdf/download.html