Test speed instrument

1) Remove the coax cable from the BNC connector found on the rear of the
speed instrument.
Bend a paperclip into a U shape and place one end of the paperclip into
the center hole of the BNC connector on the rear of the unit. With the
other end of the paperclip tap on the outside of the same connector
(essentially shorting the inside pin to the outside collar) rapidly while
watching the display. If the speed increases as you tap then the
instrument is capable of producing a speed, you should be able to see at
least a 5 knot speed with rapid tapping. If not you will need to send the
knot meter in for service. If this is ok, proceed to the next step.

2) Re-connect the cable to the rear of the knot meter and locate the
SX-120 speed sensor in the hull. Follow the cable back 10 feet and
disconnect the cable at the junction. Perform the same tap test at the end
of the cable leading to the knot meter by shorting the center pin to the
outside shell and have someone observe the reading on the knot meter. If
you can produce a good reading on the knot meter then the inter-connect
cable ($35.00)  is ok, and you will need to check the SX-120.

3) Remove the speed sensor from the thru hull fitting. Spin the
paddlewheel by hand. If the display shows a speed yet does not show a
speed when in the water then most likely the bearings are worn and will
not spin under the water pressure, you will need to replace the P-6
($25.00) paddlewheel assembly. If it does not show a speed, you will need
to replace the SX-120 ($130.00)