J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Nexus knot log

My Nexus knotmeter stopped working. The manual is sketchy on troubleshooting - says check connections (they're good), and check voltage at terminals 2 & 4, which should be 0 or 5 VDC. I'm getting 0.8V whether the paddle wheel is rotating or not.
Any ideas, or anyone have an old transducer you're willing to part with?