I recently purchased this unit and set it up in my house to practice with it. I turned the transducer transmission OFF, selected the new transducer I also purchase (Airmar B785M) and put the unit into simulation mode. I was able to use fish finder simulation for a couple of times. But today, it will not display the fish finder simulation. Even though I have the unit in MANUAL fish finder setting, the fish finder display acts like it is in an AUTO RANGE mode. It continually tries to find the bottom from 0-60 to 0-4000, but never locks into a setting and displays the bottom or fish. While it is doing this, jagged lines extending down from the water surface, appear and disappear as it moves through the different ranges. I have tried returning it to factory defaults with no success. Suggestions?