We recently purchased a boat that has a TRIDATA depth, speed, & trip indicator. We don't have an instruction booklet for this instrument. We know it worked when we bought the boat. Now the depth reading is blinking the word DEPTH and showing 0.0 feet, when we are in plenty of water. Have tried pushing several combinations of the buttons, but nothing seems to help. Does anyone have this instrument who might know what the problem is? Thanks!