Generic troubleshooting of NMEA 2000 networks

The modern yacht has more in common with the fictitious Star Ship Enterprise then it has with seagoing vessels of just a decade ago. This is due to the rapid and ongoing proliferation of networked electronics, which provide unparalleled monitoring, control, and informational display systems. The NMEA 2000 Marine Network Standard is the key and enabling factor driving the nautical trend to digital networked shipboard electronics into the 21st century. It is the international standard for marine electronics interfacing adopted by the IEC (IEC 61162-3) and is the protocol of choice for AIS products. Chances are good that it is implemented on board your boat/yacht, so let’s start out by describing some of its technical characteristics.

    NMEA 2000 is a single-bus architecture network that is based on Controller-Area Network (CAN) bus technology. CAN-bus was originally developed by the automotive industry and is also used widely for industrial applications. The signaling lines use differential voltages and are shielded from the power pair for improved noise immunity; in fact, there are three independent cable shields used on NMEA 2000 cabling. The connector pin-outs are as follows:

Pin#1=Bare Drain Wire (Shield)
#2=Red Net-S Power Wire
#3=Black Net-C Ground Wire
#4=White Net-H Signal Wire
#5=Blue Net-L Signal Wire

Be careful not to short out any connector pins while checking voltages or signal levels! Remember, if you don’t know what you are doing then don’t do anything, lest you make things worse. Don’t hesitate to seek professional help if need be!

    The power pins should read out between 9.0 Vdc and 16.0 Vdc with the optimum being around 12.0 Vdc, any lower or higher voltages are out of specifications for this standard and could cause problems with the entire system. Although NMEA 2000 uses the first 4 layers (out of 7) of the ISO/OSI network model, more than 50 percent of all problems occur in the physical layer consisting of voltages, cables, connectors, and terminators, and most owners will be limited to troubleshooting this part of the system. Troubleshooting should begin with the following questions:

•    Is the problem isolated to a single sensor, display, and device?
•    Is the problem network widely affecting everything on the network?
•    Are the power voltages within specifications?
•    Are there any error messages or trouble LED’s being displayed by your end equipment?
•    Are there any traffic LED’s blinking normally on your end equipment?

    After checking and writing down the answers to the above questions the next step should be to do a soft reset on all suspect end equipment (reference equipment manuals for recommended procedures). If the problem persists, do a hard reset on the whole network by removing power for a couple of minutes and then bringing power back up. If the problem still persists, then do a thorough check out of all the plumbing which means being sure all connector pins are clean, properly seated, and that all screw connectors are tight. Also check to see that both ends of the backbone cable have 120-ohm terminators that are tight. If the problem persists, then you may have a faulty sensor, display, or end device that needs replacing. This bad device could be improperly grounded, shorted or open causing it to malfunction and to perhaps affect the whole network. It could have a bad power cable affecting its operating voltage and thus its operation as a unit.
    In addition to thinking about the system symptoms and what may be causing problems as suggested above, here are a few more things to think about:

•    When did the problem first manifest itself?
•    Has anything recently changed?
•    Was any new software recently installed?
•    Were any new sensors, displays, or end equipment installed?
•    Do you as an operator know what is normal?
•    Was the problem caused by operator error?

    If the answer to question 2, 3, & 4 is a ‘yes’ then try and isolate anything that was recently changed and see if network problems straighten out. If this is the case, your prior changes will have to be readdressed. If the problem is still manifested after attempting all of the aforementioned steps then it is definitely time to seek a professional NMEA Certified Marine Electronics Technician (CMET) working for a NMEA member business!

About the author:
Fredrick Gary Hareland holds an AAS degree in rescue and survival operations and in avionic systems technology and is a certified marine electronics technician and NARTE certified telecommunications technician. He has served in the U.S. Navy, Coast Guard, the Military Sealift Command-Pacific and has worked for Maersk Line Limited and Norwegian Cruise Line. Hareland currently works at China Lake Naval Air Warfare Station as a microwave-communications technician. He lives in Ridgecrest, Calif.

By Ocean Navigator