sony: SRF-85 AM band repair

This radio unit was sold as in good order, however the AM (MW) band was defective. I could only hear some background noise with a constant level across the band frequencies.

Initially the unit did not work at all, but a quick inspection revealed that the headphone plug was loose in the three contacts that should be soldered on the PCB. Additionally, the cabinet had signs of heavy falls, showing a few dents and hairlines.

Being such a small circuit with minimal components, the fault would be easy to find. Indeed, the ferrite antenna two coils were broken at the support terminals (small PCB piece), again confirming the heavy falls that this unit was subjected to.

A quick and dirty fix was to remove the ferrite antenna to solder thin tinned copper wires over the broken PCB traces, and then reinsert the set into the main PCB. 

The original wax was reheated to spread on the support of the antenna, as it was before.

The AM reception was restored, where the radio showed very high sensitivity and excellent selectivity as it is expected for radios using the Sony high performance CXA1129N tuner IC.

 

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