Hi.

I have 2 Sony Car Audio head units both with faulty tuner modules. The
module is labelled TUX-020, and is listed online simply as "mounted
circuit board", it is also no longer available. I am able to get
schematics for the main unit, but this does not include any details of
the tuner block at all. I suspect Sony regarded it as a "black box".

One of the units tunes to AM stations fine, but FM reception is
extremely faint, barely audible behind the background noise. The tuning
voltage does sweep when I do a seek, and since the local stations are
faintly audible I suspect some failure in the front-end.

The second unit does not tune at all, though noise is present and
changes when an aerial is inserted. On this one the tuning voltage
remains high and does not sweep at all, obviously no reception on any band.

Car aerial has been confirmed good with a working unit. I have swapped
the tuner modules between the head units and the fault travels with the
module, confirming that the fault is with the module itself.

Does anyone have a schematic for this module? Failing that does anyone
have an old head unit with a good module (possibly one with a faulty CD
mechanism or output stage)? Or possibly some idea of where to start
fault finding? There are a lot of models from this vintage (around 1999)
which appear to use this module. If it's any help in identification, the
unit is a face-off with CD/MD changer control.

I would just buy a new head unit, but I have a 10 disc CD changer fitted
to the vehicle which is in good working order.