I have a 798c that is not working properly. I have it hooked up to an I-Pilot trolling motor. If i run it in compact side scan mode the picture is always black. If I change it to any other color, except inverse it is black. When I change it to quad beam or the other beam option, I can see struture like a normal fish finder and also locate fish. Is this something i have setup wrong or is it the 798c? Any help would be appreciated or if someone can sent me the right direction. I am in the west tennessee area. Thanks!