trouble with my 431s sonar. will be getting a correct bottom reading, lets say 15 to 20 feet, for 1 or 20 minutes then all of a sudden get a reading of 1.2 feet then may go to .6 feet then to 1 foot, i know this is wrong because i am in the middle of the lake. once it starts this it will not correct itself. i have to turn the unit off and on again for it to correct itself, which may be good for 20 seconds or half an hour. has anyone had this problem. need help. thanks.
