This radio finally made its way back to me to repair.
The cause of the problems with the set was it suffered an accidental reverse polarity.
Unfortunately the 1N4003 protection diode was not able to blow the 5A (rated) fuse and the audio amp suffered as a result.
The reason the inline fuse didn't blow is because I believe that despite being marked as 5A it looks more like a 35A fuse. Take a look at the photo of the fuse compared to the 4A fuse next to it.
The diode surprisingly didn't explode but it certainly does not function as a diode any more, it is more like a 4 ohm resistor one way and a 13 ohm resistor the other way.
Anyway a new old stock TA7222AP was fitted and the diode replaced and a 4 amp fuse fitted and the radio was working again.
The original audio IC did not fail completely as a result of its reverse polarity experience. But it was behaving in a strange way. At 13.8v it would squeal
and crackle and distort badly. If the supply voltage was turned down to 12 volts it would stop the squealing and crackling and just sound slightly distorted.
Mike