ST-60+ TriData Knot Meter Malfunction

[WEG3]

I have an ST-60+ knot meter/depth guage and the speed display no longer functions normally. Speed will not register unless I remove the transducer, spin the paddles and return the unit to the hull. Speed will then be displayed for about 5 minutes, then reset to a decimal (e.g., 00.09) then countdown to 00.00 where it remains until I go through the removal/spin routine, speed shows for another few minutes, resets and again counts down to zero. The paddles move freely and are not fouled (I did apply transducer paint to reduce fouling which I've done in the past without a problem). Wires appear fine. Any suggestions?