Sony XR-410 car stereo with no FM

[lineslim]

Hi,

Im trying to fix an old car stereo, Sony XR-410. Cassette player works fine but there is no sound in FM mode altough the frequency is displayed. Also only the button for changing between AM/FM seems to be active.

I saw there was a tip about this issue in som kind of commercial database "Aswo Euras" for which you needed a subscription (not worth it im my case)

Does anyone know which component may be the cause of this problem?

[torbjorn]

There is no specific component that can be directly pointed out as a common cause for no sound on FM , instead you will have to troubleshoot the FM radio signal chain in the traditional way. First, check out that all circuitry (front end, IF chip, stereo decoder) gets correct supply voltage.
Check if there is noise or audio at the demodulator output. If you have audio there with the radio tuned to a strong station, then follow the signal through stereo decoder, AM/FM/tape switching circuitry etc to see where it disappears.

If you get only noise out of the detector but no audio, then it is possible that some squelch circuitry mutes the LF signal. In this case, try injecting a modulated 10,7 MHz signal at various points (IF inputs, at the ceramic filter, and so on). If you don't have access to a signal generator, you can take 10,7 MHz from the demodulator coil of a working FM radio.

If the entire IF strip is working, then the problem is probably in the front end. Perhaps the local oscillator doesn't work or the HF transistor has been blown due to a ESD discharge at the antenna input. Also, the varicap diodes may fail due to ESD.

[Guest]

Hi Torbjörn.

Thanks for taking the time to write such a good detailed answer. Im afraid however my electronics knowledge is limited to changing a known suspicious component or visually inspect for bad solders or similar so I may have to consider myself beaten by this problem.