I posted a question earlier about my 728. After futher inspection I have found that when you turn it on you can feel the transducer pinging but no depth shows on the screen. It will ping for about a minute then it stops pinging and the depth displays anywhere from 700 to 1190 feet . I have checked the transducer cable and it is not nicked or crimmped and it is no where near any kind of power. I have set it back to default mode with no change. Help!! Is it the transducer or the head unit ?