Check all your wiring and where you have the transducer wire routed. Friend had a unit that had problems and sent it back to H/B a number of times. Each time they found no problems. When they receive a unit, the first thing they do is restore the defaults. That usually clears up any problems do to electrical interference etc. It turned out that he had a jumble of assorted wires under the console with his excess transducer wire in a coil with all the other wiring. I guess electrical current was scrambling the brain of the H/B unit. Once the defaults were restored, it would be okay for a short time, then go goofy again. Pretty sure in the installation instructions, there's a specific way to deal with excess transducer cable. When your friend tries his unit on your boat, it probably isn't on long enough for the electrical interference to mess it up. If you find a place where the wiring is bundled or touching, fix that and do a restore defaults and try again.