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?

I had this happen to me and it was the paddle wheel sticking against the sender. I bought a new paddle wheel and that stuck as well. Ended up sanding down the edges of the paddle wheel now it spinns great.

I guess the senders must swell with age??

I lifted this from the Cruiser's forum:
Don't know what model you have yet if you remove the case and use a DVM having a Hz display mode (frequency) you can measure between the black negative wire (leading from inside where the transducer wires are lead to the pcb) and the center of the coax wire. Move the paddle wheel and you should see a few Hz response on the DVM.

If you don't have a frequency mode the next best thing is to use the ac input voltage mode. Again, spin the paddle wheel and look for an ac voltage. The meter in this mode will not read accurate low frequency very well so use a sensitive scale like 100mV to look for a response.

No response indicates either a bad coax or transducer. If you have a good response then the problem is in the instrument. I have some schematics of some of the knotmeters and can help troubleshoot further on the instrument depending upon your ability to troubleshoot and repair. Otherwise you will have to send it in for repair.

If the problem is not the transducer or cable be sure to inspect the connector at the instrument as well as the inside wires of the instrument for any indication of corrosion or water intrusion and remove it with Corrosion Guard or a similar product. Do not use WD-40 or just water. These will cause other problems later even thought many mariners routinely use WD-40 in ignorance (yeah, I know that it is better than nothing just like a monkey wrench is better than not having a proper box wrench).

Thanks for the response. My paddle spins freely, but the cable is not a coax, it has 3 conductors plus a shield. Nevertheless, I'll try your suggestions. No idea what the model number is -- the manual just says Nexus Multi Control Instrument and Server.
Thanks.

just went thru this,,,
i was able to get some readings when i wiggled and pushed on the wires as i spun it,,,,
the replacement is just under $200.00 i got mine from Chicago Marine http://www.chicagomarineelectronics.com/NexusClassicSystems.htm#8

there are 2 sizes, 43mm is the older one. (not curently being made if i remember correctly)

One of the conductors is for the thermister, one is a common and one has the paddle wheel pulses. Mine died from years of removing it between races. On the new one I built up some silicon to "strain relieve" the wire as it leaves the housing, so far so good.

I spoke with Chicago Marine Electronics yesterday, and we concluded that my transducer is shot. Price has gone up to $255. Still less than a whole new set of instruments.