NMEA 2000 not working, all devices missing

[billrh42]

About a week ago I re-installed my VHF radio and AIS 600 as they both had the MMSI number updated to a FCC number. After installing the units all the boat's NMEA 2000 components were linked up and present in the device list on the chart plotter. Yesterday while I was checking out the gear I noticed that none of the devices are showing up anymore. The VHF radio is not connected to the chart plotter nor is it picking up a GPS signal. When starting the engine there is no engine data showing up and the low-oil alarm is going off. No AIS boats show up on the charts, etc.

Today I checked for power. I checked at the fuse block, on the backbone and the cable going to the chart plotter. All had 12.5-13v. Since the last thing I did was add back in the AIS and Radio, I disconnected them to see if that fixed it. It didn't.

At this point I'm considering disconnected each cable, one at a time, to see if a unit is messing with the signal. There are 10 devices connected to the buss. I'll also be checking the termination resistance the next time I go out, but I don't think that is the issue.

Any other ideas that I should consider? Has anyone had a single NMEA unit take down the entire network?

-Bill

 

[Full_O_Fish]

Have seen just about everything...
-Bad tee not passing power to all or part of the network.
-Too many terminators causing collisions and fast packet errors eventually freezing the network.
-Too long of cable used as drop instead of backbone.
-Internal short in a device taking the network down when connected.
-The list goes on and on...

I would recommend checking as you have mentioned, isolate the network down to just power and a single device and add devices till it stops working. Also, try changing the tee that power is connected into.

 

[billrh42]

Solved

I measured the termination resistance and it was in the meg ohms which told me that one or both of the signal lines had lost contact. Since it's a 14 year old boat I decided to replace 8 of the tee connectors with 2 4-way tee connectors and also replaced the terminators. I assembled the backbone on a piece of plywood and screwed it down. Once I had all the cables disconnected from the old backbone I installed them one at a time, labeling each one once I figured out what it was for. Then I screwed the new plywood/backbone back where the original one was. It took the entire day to do this, mostly due to the difficulty at getting to all the connections but it was sure satisfying to see all the electronics came back to life.

I probably could have just tried retightening each tee connector until I found the issue but I didn't really trust the 8 tees ganged together and held tight with tie wraps and 3 screws.

-Bill

 

[SJI Sailor]

Thanks for sharing the solution!

And a nice thing about the 4-plug Ts is that they are not only easier and (presumably) more robust but also need less space. I switched to that when we added a couple of devices and the extra space helped.