Wind instrument malfunction

[Bill Plaia]

The only issue I see is that the supply voltage is .09V below the standard. I have measured it at the iTC-5 as well as at the junction box. Both voltages are the same at 7.91 so there is no voltage drop in the wire, at least to the base of the mast. The iTC-5 provides the power to the mast head transducer. I spent a portion of my life as an electronics technician so I know how to use a multimeter.


Is there a schematic available for the iTC-5 and the masthead unit? I'm making some assumptions based on the outputs that the iTC-5 has high impedance A/D converters to read the voltages. If this is correct I should be able to test the iTC-5 by applying a constant voltage within the appropriate range to the input. I would use a 1.5v battery with the negative referenced to the shield for the speed reference and two in series for the directional tests. If the software does a comparison between the left and right side and requires a minimum of 2v on one side I can make a voltage divider and supply 2v to one side. With all sensors disconnected from the iTC-5 each of these voltages applied to the inputs should give me a constant reading. If output of the iTC-5 continues to vary wildly or does not read at all the iTC-5 or the I70 is the problem. Let me know if you see any problems with this plan. It would be nice to be able to see the raw NMEA sentences this thing was putting on the bus, but I can't find anything in the documentation that would allow me to do that.

Just to add some additional support for the interference theory I took the boat about 10 miles away today and the wind instrument appeared to be working fine when more than 5-6 miles away from my current location. On my return the instrument stopped working again in pretty much the same place that it started working on the way out. I don't have an o-scope on my boat or I could look at the output from the Masthead and see if there was a lot of noise on the wire. I did a lot of work with A/D in my technician days and know that while you can't see the noise on a multimeter, it can cause havoc with an A/D converter. Can you think of any circumstance where a problem like this can be location dependent without influence from an outside source such as radio interference?