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Old 12-07-2018, 05:52   #1
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Troubleshooting NMEA 2000 and the troubles with NMEA 200

So I have an intermittent fault in my NMEA 2000 network and it is driving me crazy on two fronts.

Firstly, tracking it down is proving to be stupidly time consuming. It appears to be heat related. I had a bunch of junctions in the engine compartment, with drops from the rudder feedback, GPS antenna, and plotter joining the backbone and after running the engine for an hour or two the network would flake out.

I moved the junction out of the engine compartment (but not as far as I would like...it's in an area that still gets at least very warm) and had a blissful full day of sailing...and then after another couple of hours motoring at the end the network again went down, of course just when i was entering port with shallows...and no depth sounder. Has anyone heard of or experienced heat-related issues with NMEA 2000 cabling/junctions?

Fortunately, the plotter also has it's own built in GPS receiver, but I lose depth, wind, AP.

So I assume there is no magic bullet to this...I have to start pulling T's and sensors and so forth, and swapping cables, until I find the culprit. Most of the cabling is less than a year old so I doubt dirt is an issue. It's not termination issue and all connections are tight and secure. If anyone has any tips on how I should proceed I'm all ears. There appears to be precious little info on the net about troubleshooting procedures for NMEA 2000 other than the "yank and see" method. With a fault that takes hours to surface, this could take a long time.

Secondly, how did we get here? NMEA 2000 seems great at the dock but my God, talk about an Achilles' heel for your boat systems. One little network gremlin and ALL your systems go down, with all the sensors connected to the backbone instead of to their head units. Who's brilliant idea was this anyway? Any suggestions for increasing robustness, other that completely separate systems?
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Old 12-07-2018, 06:26   #2
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

Do you lose every device or just some devices? That's the first question to ask. If only some, make a list and compare that to the network diagram.

If you lose every device except the plotter then it would point to an intermittent termination. But you say terminations are ok. How do you know that?
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Old 12-07-2018, 06:42   #3
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

Dan,

I have a plotter, two mfds, and a vhf with built in AIS and an AP. When the network faults, the plotter shows nothing external on the network device list, the mfds go blank with no data, the vhf no longer receives position data (from eith if two available sources), and I get an alarm for no AP computer.

I suppose I might have a bad terminator. Thats easy enough to swap out at the boat level end. The other is in the masthead sensor.
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Old 12-07-2018, 07:05   #4
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

Checked the power supply to the network? It may also be possible that a short in a cable could also block all connections. For multiple failures, an open cable would have to be in the backbone of the network.
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Old 12-07-2018, 07:15   #5
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

The two mfds (which powered by the network) are getting power but no data. Also, this faults after a period of time, and *seems* heat related. Im leaving the instruments on indefinitely right now to see if I get a fault without heat...was loathe to before as Im at anchor.

Occasionally, I will turn on the network (its on its own breaker, which it shares with a gofree wireless bridge) and the mfds will light up but show no data. Cycling the breaker fixes that.
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Old 12-07-2018, 07:24   #6
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

Would it be possible that the network power voltage is dropping too low? Sometimes additional power connections are needed in some installations. You could progressively disconnect gadgets from the network and see if it comes good. Might want to grab a can of freeze spray also. It'll assist in hunting down a heat related issue.
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Old 12-07-2018, 07:33   #7
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Troubleshooting NMEA 2000 and the troubles with NMEA 200

Its a fairly small network. Only loads are the two mfds, three sensors (wind, speed/depth, and rudder feedback) and AIS antenna. If it were a power issue I would not expect it to work fine for hours and then fault.

Freeze spray may help, will grab some when I can.
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Old 12-07-2018, 07:59   #8
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

OK I'm now suspecting the masthead connection. The stick was down for a year with the simnet cable dangling exposed. I did not clean the female sockets before reconnecting in the rush to get everything ready to step the mast.

Would result in bad termination, which i think would explain everything getting power on the network but the plotter and mfd's not seeing any data from other sensors/devices. Yes?

Up the mast I go. Any advice on cleaning the sockets for the pins? They be tiny....

And thanks everyone for the input and advice. I appreciate it very much.
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Old 12-07-2018, 08:10   #9
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

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Originally Posted by Suijin View Post
OK I'm now suspecting the masthead connection. The stick was down for a year with the simnet cable dangling exposed. I did not clean the female sockets before reconnecting in the rush to get everything ready to step the mast.

Would result in bad termination, which i think would explain everything getting power on the network but the plotter and mfd's not seeing any data from other sensors/devices. Yes?

Up the mast I go. Any advice on cleaning the sockets for the pins? They be tiny....

And thanks everyone for the input and advice. I appreciate it very much.
I would proceed with caution. Today connections are usually gold plated and abrasive cleaning often just removes the gold and leaves a brass surface that is much more susceptible to corrosion. I think your problem is unlikely to be a simple connection issue especially one at the top of the mast. It's a long way from the heat of the engine!
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Old 12-07-2018, 08:33   #10
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

I forgot to mention that it faulted again without any heat from the engine. But I'll proceed with caution if I clean the connector...I don't want to buy and run another mast backbone cable lol
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Old 12-07-2018, 09:01   #11
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

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Originally Posted by Suijin View Post
OK I'm now suspecting the masthead connection. The stick was down for a year with the simnet cable dangling exposed. I did not clean the female sockets before reconnecting in the rush to get everything ready to step the mast.

Would result in bad termination, which i think would explain everything getting power on the network but the plotter and mfd's not seeing any data from other sensors/devices. Yes?

Up the mast I go. Any advice on cleaning the sockets for the pins? They be tiny....

And thanks everyone for the input and advice. I appreciate it very much.
Good fault finding by process of elimination and logic. I think you have it nailed. You could try cleaning all connections from your depth and wind instruments, just isopropyl alcohol on a swab should do it. If you use a cotton swab, be sure to blow out any tiny fibers from the swab that may have been captured in the sockets. Foam swab is better. I've used foam swabs in my work in the past, but don't know where to buy them retail.
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Old 12-07-2018, 09:21   #12
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

I have what I would guess is a far simpler network, but with perhaps 12-14 T connectors running off to instruments, autopilot, and sensors.

When I had a balky masthead sensor, I found that I could disconnect the network in various places, and if the offending item was then out of the circuit, the rest of the stuff would work without termination at the point where I disconnected the network.

This allowed me to find the offending node (may not be the right word) quickly. Perhaps I could have done the same think by inserting either a male or female terminator, but it worked to have an open network.

I hope this simplifies things for you somewhat.

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Old 12-07-2018, 09:27   #13
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

When the network is faulted, you could remove one device at a time and check to see if the network is restored.
You could disconnect the masthead wind sensor and terminate the backbone where you disconnected the wind instrument.
Sensors and instruments connected to the backbone with a T can just be disconnected without the need to move the backbone termination.
If you can start by breaking the backbone in half, that will also half the number of sensors you have to check, then break the remaining backbone in half again each time connecting the piece that contains the bad device and so on and so on.
Also make sure your software is up to date.
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Old 12-07-2018, 09:38   #14
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

I have NMEA2K on our boat and even when the wind sensor loses its wireless connection to the mast head sensor everything else stays up. Since you don't seem to have issues when sailing, I would not suspect voltage, corrosion, etc. at first unless you are right on the edge. (You power injector is towards the middle of the backbone, right?)I'd look where the cable comes through bulkheads, etc for wear. If your engine is like ours, it makes the boat shimmy a bit when running. You may have a lose wire inside a connector that the vibration shakes a little lose when running. Try jiggling the cables a bit and see if you can recreate it.
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Old 12-07-2018, 09:48   #15
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Re: Troubleshooting NMEA 2000 and the troubles with NMEA 200

Can you temporarily disconnect the mast cable and replace that with a termination? Then run the network for a while to be sure the problem really is up the mast.
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