is the transducer
inside the hull
? If so it might be dried out so no signal is sent. if you can remove it Coat the bottom with vaseline or put a bit of cooking oil
in the bottom of the socket or box or whatever it was in. it should then start to register. if it is mounted through the hull
the transducer might be dirty or covered with something. Is the Boat in or out of the water
? If out it won't work! Hope this helps and you don't have to replace the whole thing.