Hi Clarence
Although the problem COULD be a faulty depth transducer, in my experience this is usually caused by a cabling problem, either there is a poor connection at the display unit, a poor power cable connection, RF interference from another device or the cable has been pinched causing an intermittent fault. After making SURE the power cable is tight, I'd clean the connections, then inspect the cable looking for an area that has been stressed. If you have a VHF radio nearby, try shutting that down during your testing. If depth reads normally, you know where your issue lies.

Good Luck!
-Steve