Defective metal detector (Littleover DE23)

Very old CScope metal detector which at the present time does not work. It needs four PP3 batteries. There are three batteries on their last legs with it but just one needed to complete the circuit. Sometimes when switched on (with 4 batteries) there is a continuous signal and other times nothing. Rather than dispose of it someone might light to have a go at restoration. The threads of the extending arm are are worn. Collect only.