chuck ive been using the same humminbird wide 480 fish finder for almost 10 years. the problem you had ive seen several time before and it can happen to any make of fishfinder its not because it was a humminbird that it had issues. what usually causes that is a short in the circutry which can happen im sure for a number of reasons but the few fishfinders ive seen had one of these 2 reason. first reason is the fish finder was hardwired directly to a deep cycle batter if it would have had a inline fuse or breaker of 4 amps or less it would have prevented the problem. the other one the co-ax cable to the transducer got a kink in it which cause the casing in the cord to expose the core wire and it shorted with the other wire in the cord. which I had this happen with a bottom line fish finder a couple years ago because I had tryed to make it into a portable unit so the cords were loosely strung out throughout the boat.