Troubleshooting NMEA 2000 and the troubles with NMEA 200

[geekoman]

A technician on board showed me that you can see the supply voltage via the MFD. If you can configure your display to show various pieces of information (e.g. depth, temp, windspeed), there is also one to show supply voltage.

Did you check your network diagnostics? When you say it is working, there should be no Rx/Tx errors, and lots of packets being transferred.

[transmitterdan]

What is the battery voltage when charged up after a few hours motoring? Does the regulator drop to float voltage?

[Suijin]

Dan I don’t know for sure but 13.xx I’m fairly certain.

Yes I’m getting fast packet errors and Rx errors but no TX errors. Also interestingly the “bus load” pops up sporadically to 99.9% which strikes me as odd as it’s a pretty modest network.

[geekoman]

If I recall correctly, the fast packet errors not a big deal, but the Rx is. See if you can take devices off the buss until errors hit 0.

Can you validate the data line resistances? I wonder if the resistance is high (i.e 120 ohms instead of 60 ohms), the system see loading go up because current goes up? I am not sure how it measures loading. Packet count? Or, some electrical measurement (current, voltage)?

My loading was always less than 20%. My system is configured as shown in the schematic I previously uploaded. Seems like I have more devices, so a high loading may be a clue.

[geekoman]

I remember getting error count increases every 20 seconds. Then determined the DST 800 updates every 20 seconds. It was one of my system's issues. Unplugged DST, those errors went away.

Have you ruled out the MHU? With the MHU's susceptibility to lightning strikes (that was also one of my issue) and the long cable length, there are many potential contributing factors. Its tough to swap out and MHU cable, that is why separating it and verifying it is not the issue is golden. It would be ideal if you can create a system with terminator + MFD + power + MHU, and demonstrated it worked with no errors. Minimize any other items on the bus.

If you are getting any Rx/Tx errors, those are you focus points.

Also, your getting Rx/Tx errors without heating up the system? That's good, as you might be able to identify the culprit(s) without having to go for multi-hour trips.

[Suijin]

System has been running for two hours at anchor, no errors and bus at 12%.

One time it faulted and I took out a cluster of T’s/drops and it started up fine. Put them back in and it started up fine again. That’s when I thought it was a heat issue. Moved the cluster to a cooler location and the problem did not resolve.

Next leg is a long trip down the Delaware. If it faults again I’ll pull the MHU and check. Then start pulling other stuff. Will have to drift a bunch without an AP lol.

Thanks for all the advice. I really appreciate it.

If I can’t fix this by the time I get to Cape May I might bite the bullet and hire someone to take a look, if I can find someone there. With all the sport fishers there there has to be someone...

[transmitterdan]

In the past I have been able to easily find faults on a CAN BUS system using an oscilloscope. Just looking at the waveform on each of the 4 wires and comparing will often reveal the problem. Then start unplugging devices one at a time and see when the bad waveform cleans up I have found the bad device.

I realize an o-scope isn’t going to be in most cruising boats. But they are effective at revealing bus problems.

[geekoman]

With a spare terminator, pulling the MHU is easy. If the problem resolves itself, you've really narrowed it down.

Good luck.

[Suijin]

I think I found the culprit. A third Maretron field connector that I forgot about, on the Precision 9 compass, that fits through a cutout in the wood bracket. It was cross threaded onto the compass and not fully seated but impossible to tell without removing the bracket. Took it off and put a Lowrance female end piece on with a temp terminal strip.

I hate the Maretron fittings. Not only is it brain surgery getting one on, but the collars are metal and you have to be careful screwing them on plastic fittings. Happy to have it gone.

As hour with no faults, bad packets, Rx/Tx errors.

[geekoman]

Good news! Now you know more about your system than you did before. It will be helpful in the future when you need it most!

[Suijin]

Well I put the whole system in myself...just didn’t do it right lol. But I suppose you’re right. Just have to pray that I really did fix it. Will know tomorrow.

[geekoman]

Good learning event!

The other learning I had was to be confident that I could eliminate any part of the system that goes bad when offshore, with relative ease. And, to me that meant isolating the mast head unit. You cannot just unplug it, you need that terminator, so I have an extra. I also carry a spare 7 way connector, and a cable - Simnet components. With those items I could isolate a small navigation system (chartplotter + working sensors + autopilot) - not ideal but better than no functions at all.

[Suijin]

Yeah I need some spares now. I take it having empty sockets on the 7way connector is not an issue?

[geekoman]

Right, empty sockets are not an issue on the 7 ways. They make plugs that can be inserted into the empty sockets (noting electrical, just a plastic plug). I was told they were not necessary in dry locations.