An American amateur has given his answer to one reason why the 706 can
go deaf on 144 Mhz. It because of two small sm coils becoming detached
from the main circuit board.
The coils are located under the power supply socket which will need sliding up from its location to allow the sm coils to be resoldered.
In my opinion the reason the coils become detached is due to faulty mechanical design. If the set is used moible frequently, with the constant removal and replacement of the power connector the socket bends and then comes into contact with the coils which get loosened from the circuit board.
The permanent cure is to fix the power socket with hot melt glue at the top of its vertical travel when it will not then come into contact with the coils.