NMEA2000 troubleshooting - will I burn anything!?

[antaris]

Hello there,

My Garmin GMI10 display (which has been, generally speaking, great so far), stopped showing wind direction and speed, while racing last Sunday. The depth and temperature are still there. I therefore presume that the cable has some sort of discontinuity somewhere between mast and instrument.

The question: with the power ON, can I plug/unplug NMEA 2000 cables or do I risk burning/overvotage?

I want to mark each cable... and then check the connections...

 

[AngusMcDoon]

It will be fine with the power on. You won't do any damage. With a network disconnected half way you may stop all data transmission though as the terminating resistor will be disconnected.

 

[Norman_E]

The terminating resistor at one end of the backbone is at the masthead because only the backbone can exceed 6 metres, which is the limit for drop cables. If you have the Garmin wind transducer it is actually fitted with an in-line terminator and an in-line lightning arrester at the masthead between the backbone cable and the transducer. If the connection is broken between the terminator and the transducer you will get no wind direction or speed, but other NMEA 2000 network sentences will still be readable.

 

[antaris]

Many thanks for the replies - so that means I am going up the mast on Saturday...great

Strange that even with the terminator disconnected I should be reading the other network data. I'd imagine that all data should de gone! Oh, well, let's see...

 

[AngusMcDoon]

I'd imagine that all data should de gone! Oh, well, let's see...

Not necessarily so. Without a terminator the signal will reflect off the open end somewhat. This reflection may or may not be strong enough to garble the message, and the reflection may or may not be sufficiently time shifted to cause interference.

 

[Norman_E]

Many thanks for the replies - so that means I am going up the mast on Saturday...great

Strange that even with the terminator disconnected I should be reading the other network data. I'd imagine that all data should de gone! Oh, well, let's see...

Though I suspect that the trouble is at the masthead, before you go up check all of the connectors to see that they are properly fitted, starting with the one at the mast foot where the long cable up the mast is fitted. Check carefully to see whether on installation someone cut the mast cable to enable easy fitting then joined it. If it is the Garmin cable it came with a "Field Installable Connector", if so make sure that it has had all the wires properly connected and that none have moved.