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NMEA SIMNET bus just died
I recently purchased our Lagoon 450 (used) and it has a suite of B&G electronics on board connected via Simnet. It started to act erratically by the primary displays (Zeus 2 and Triton) not recognizing some of the equipment (wind MHU - B&G 508). Now, the VHF Radio (V50) cannot find GPS information, and does not show NMEA2000 as a GPS source - in radio setup.
I think this may be related to the MHU being damaged/disconnected/failed and the bus loosing the terminator supplied by the MHU, and connected to the Simnet bus. I measured the bus resistance across the data lines and see 118 ohms, which I think is a symptom of a missing terminator.
I am in the process of obtaining another terminator to help with additional debugging, before heading up the mast.
If I disconnect the MHU, some of the equipment is recognized (AutoPilot - AC42, rudder sensor, sonar hub) but not all (i.e. VHF radio, depth/speed transducer - DST200, AIS transceiver - NAIS400).
Am I on the right track?
Your troubleshooting sounds smart to me. Improper termination and unsound connections are often the cause of N2K issues. But your situation also reminded me that Simrad apparently produced a "noise filter" at some point to help with issues arising from long SimNet backbones, info here:
Thanks Ben. I’ll ask about the N2K filter when I talk to B&G tech support tomorrow.
Reflections make sense to me, maybe some devices are more sensitive. Bad terminating resistor is an easy, maybe not cheap, fix. Best case, at this point, in my mind, is cable to wind unit on mast became disconnected.
Getting a terminator has been a project. Might have one tomorrow.
Do you know where your terminators are now? I assume there is one somewhere not in the mast, and potentially two, with the third up the mast being an extension/bridge of the network? Can you isolate the section going up the mast from a tee and see if things work without the MHU connected?
Yes, I know the placement of one plug type terminator. I’m told, and the topology supports, that the other terminator is in the MHU. I do not see a third. Can there be three,and operate properly?
I purchased another plug type terminator, and it arrives today, hopefully. It will help debug this problem, and enable me to isolate the MHU, if needed, in the future.
I’ll go up the mast, weather permitting, today. Hopefully, the connector became disengaged and the fix is simple. It is a type 508 MHU. Any guesses on most likely issue? I wondering what tools to take up. Any suggestions on how to improve the connection security? I have not been able to find any detail images of the assembly.
Does anyone know if it is reasonable to expect some of the devices to operate properly (I.e. be recognized by the MFDs), and not others, if a terminator is missing?
Yes, Mark, I'm pretty sure your SimNet MHU has termination built in, as indicated by its red accented connector and shown in the SimNet manual:
Inserting your new terminator where the mast SimNet cable usually attaches will likely confirm your hypothesis. I.e., the smaller, correctly terminated network should work fine.
Hopefully, you will find the SimNet connection at the masthead detached or loose. I'd take spray electrical contact cleaner and any very small brushes I could find for the connector cleaning, then dielectric grease for the reattachment.
PS No, there can not be 3 terminators on a single NMEA 2000 network; I think Steve misspoke. Also, on sailboats with N2K masthead sensors, the backbone (or trunk) invariably goes up the mast because drop cables (also called spurs) are quite limited in length. You can use special hardware to extend a backbone, but you don't add terminators.
Ironically, a way to get the thin cable advantage of your B&G 508 -- current B&G wind sensors don't use SimNet cables -- is with a NMEA 0183 ultrasonic sensor from LCJ Capteurs, which uses a WindyPlug 0183-to-N2K bridge down inside the boat. One is testing well on my boat and I tried to explain here:
Many setups have a separate NMEA 2000 network for the wind instrument, with terminators on both ends, and a bridge connector between that network and the network not-in-the-mast. That's what I was wondering about in this particular setup - finding and identifying where the terminators are would help rule out whether there were two segments with 4 terminators, or just one with the terminators being at the masthead unit and then somewhere in the boat down below.
With the hundreds of NMEA 2000 networks I have troubleshot, the first things I do is look for terminators, and then get a device on the bus to see what is going on.
I have the same LCJ Capteurs + WindyPlug that I put on my boat recently during my major mast work. It solved the same challenge of either making that the end terminated section with heavier NMEA 2000 cable, having two networks bridged together, or other less optimal solutions.
Adding the new terminator, and eliminating the MHU from the picture helped. I have the MFD seeing everything except the NAIS 400, the V50 radio, and the radar. Seems the RI10 radar interfaces N2K connection was causing some RX/TX errors, so I disconnected it. Now the Autopilot was connecting consistently.
I wondered if the bus was overloaded (current wise) and was dropping the voltage. Causing some of the equipment to drop out.
I plan to call B&G support in the morning. Current symptoms are:
1. V50 not finding a gps location. V50 not recocoognized on N2K buss via MFD. Tried two different cables. Maybe an EU configuration. Can I modify this programmatically?
2. MHU issue. I’ll climb up the mast ASAP to check this out.
3. NAIS not recognized. I tried to do a software update and now the system does not even respond. Hopefully I did not “brick” it.
4.Radar - the radar was conflicting with the Autopilot. When the radar interface,RI10, was connected via N2K, I would get “autopilot not found” alarms. I saw that there was a software update for post 2014 radars, and my boat is 2016. I applied the update, and now it say “radar not found.” Hopefully just a reset and discovery process.
5. Need to update the MMSI number on my NAIS. Minor problem as I do not think it impacts functionality. So, low priority.
Any insights would be highly appreciated.
Is there any commonality among the devices that are still not seen from the MFD? Are they past a certain point on the N2K backbone? Connected via a common tee-connector? Powered on the same circuit (unlikely to be the source of trouble, just reaching)?
Next thing I'd do is try to simplify things. Get a properly terminated N2K network with just the MFD on it, then add devices to that network one at a time. Try connecting just the V50, is it seen? Does everything work with just these two devices connected? From there you can assess the functionality of each device and the MFD alone, then begin adding multiple devices and see if there's a pattern to be found there. Frequently this exercise will quickly point you towards the troublesome device or connection.
Contributing Editor, Panbo.com
I think Ben Stein's advice is very sound, but I'll add a few thoughts:
1. It sounds like you know how to use the Zeus2 Network/Devices menu to see individual devices on your SimNet backbone. Somewhere there is a figure for network traffic %. Keep an eye on that as you try new devices. A messed up device causing extraneous traffic could be blocking other devices from joining the network.
2. Maretron's N2K install guide is a great reference: https://www.maretron.com/products/pdf/Network%20Installation%20Guide.pdf
3. Consider using Maretron's free N2KBuilder program to diagram your network (it will also flag potential issues): https://www.maretron.com/products/N2KBuilder.php
4. Now your MHU looks less guilty, so masthead trip is lower priority (but you could try it on the network).
5. The RI10 may have issues beyond whatever is messing up your N2K network, so add it gingerly.
Hope you find the culprit!