My brother has a Lowrance X 510c mounted with a relay switch and two transducers front and back. He just re-carpeted his boat and when he used it for the first the transducer on the back showed fish icons(I know ,shouldn't use them). When he switched to the front, this transducer did not display icons.....Is the transducer bad?.... It shows depth and bottom contures.....Could it be hooked up wrong or what ever?......crappie1133