I bought a boat a few years back and with the boat was an Autohelm depth sounder. It has been working faithfully until a few days ago when I switched the depth sounder on a message came out "Enter Lock Code" . I am puzzled as I had not set any code and this has never occured before. After sailing gor a few hours, the depth meter indicated normally again. Is there anyway that I can reset the meter ? I had tried various combinations without success.