I have an old fcv-582L on my scarab with an in hull transducer. I took the boat out yesterday and am not getting any readings on the screen, no depth measurement or any other info besides a . The screen lights up and when I put it into auto mode it tries to read at 3 or 4 different depths and then just gives me a flat bottom shot. Does this mean I simply need a new transducer? My current transducer has 2 steel handles on it and is about the size of a brick. If I do need a replacement which model would be a drop in replacement?