I am a SAMS® Accredited Marine Surveyor, ABYC® Standards Accredited, a Yamaha Certified Outboard Engine Technician, a Mercury / MerCruiser Certified Technician, a Honda Certified Outboard Engine Technician, a ITC® Certified Level II Thermographer, holds a USPAP® Certificate on Appraisal Standards, a USCG Licensed Master Captain, and a member of SAMS®, ABYC®, IAMI®, and the NFPA®. We specialize in surveying and inspecting boats for overseas buyers in Europe, Asia, Australia, and Africa. We provide our services in the United States, the Caribbean Islands, Puerto Rico, Belize, and Costa Rica. I am a USCG licensed master captain and provide charter and yacht deliveries for both power and sailing vessels. I also provide service and repair services for gasoline outboard and inboard engines. We offer pre-purchase, insurance, valuation, damage claim, marine engine diagnostics, and ultrasonic marine surveys. I own and operate a marine surveying and consulting firm based in Palm Beach Gardens, Florida. By isolating and disconnecting each “T” connector (if there are multiple backbones on board) one by one until the oscilloscope shows clean data is how you find the problem. Lines that run into each other, in consistent high / low digital data (not alike on the high and low sides), and spikes in the data show that there is corrupted data. Connecting the oscilloscope to the NMEA 2000 backbone allows you to see this data while you trouble shoot the system. This is what causes digital gauges to not work properly, freeze, etc. When a “T” connector, wire connection, terminator or gauge malfunctions, the data becomes corrupted and this clear high / low data can not communicate clearly.
The resistance is 60 ohms in the NMEA 2000 backbone system. The two voltages on the high / low mirror each other to confirm accurate data to the ECM.
The system runs off a high / low voltage system (low is 1.5 – 2.5 volts and high is 2.5 – 3.5 volts). The photo above is what corrupted digital data looks like. What you are looking at in this photo above is an Evinrude E-Tec 50 HP outboard engine connected to digital gauges through a NMEA 2000 backbone connection. This is what DC electricity looks like using an oscilloscope. What corrupted digital data looks like on a NEMA 2000 system
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