I have a Humminbird 967c which has developed an issue, the head unit is not recognising the transducer, a message appears on the screen at start up which reads transducer not connected, the unit stays in simulation mode, it does this in air. I have a second 967 unit which does not do this, the unit recognises the transducer and goes into normal mode while the unit is in air. Any suggestions or is this a return to humminbird, any thoughts would be appreciated.