Is my Sony XR-7500R Car Cassette Radio mendable?

If I describe the symptons of my problem perhaps some kind soul might be able to tell be whether or not it's terminal!

The cassette works fine.
The radio does not produce a sound but the display shows a radio station connected which changes when I press any pre-set button or press the seek button. Also, when I turn up the volume the volume indicator moves along as normal. Also, when I switch into radio mode the electric aerial goes up as normal.

Someone has suggested that the tuning chip is defective.

Thanks.

Peter Foster
November 2009