Beyond these considerations, the systems of
today are really “black boxes” in the sense that
the high-tech side of things is literally “in the
box” and not field serviceable. As a trou-
bleshooter, your role may consist of nothing
more than being able to trace and confirm that
the connections are in the proper order and
there are no breaks in the length of the wire
running between points A and B. As with
shore-power AC systems and traditional DC-
distribution systems with their relatively large-
gauge cabling, the vast majority of problems
in data networks will almost always be “at the
ends,” or termination points. (There is also the
possibility of physical damage to a cable run,
but this will often be obvious from a simple
visual inspection.) Your tools of choice will be:- TDR
- tone-generating circuit tracer
- ohmmeter
- voltmeter
Here are some basic guidelines: - Use a TDR or tone-generating circuit
tracer (described in Chapter 3) to trace
the cables and confirm the integrity of the
wire run. (You can also use an ohmmeter
for this task.)
If you use a TDR, remember its mini-
mum operational length requirement is
9 feet (2.7 m). Many of the cable lengths
you might be testing are less than 9 feet,
so you will have to add a 9-foot length of
cabling to one end of the cable being
tested to get relevant readings on the
TDR. An easier and more practical option
is to use a tone-generating circuit tracer or
ohmmeter to “pin out” the harness. - Use a voltmeter to test that any distrib-
uted power is within acceptable limits. - Look for solid continuity from a pin ter-
minal at one end of the harness assembly
to the corresponding pin at the other end.
Do a wiggle test (see Chapter 15) at the
plug assembly with the meter attached.
Wiggle the plug assembly while observing
your meter to see if the wire being tested
alternates between continuity and open
circuit. Remember almost all harness
failures occur at the plug ends.- Confirm that the various wires are con-
nected to the correct terminals, and that
the individual wires have good continuity.
Operational power for the various pieces
of equipment in most networks has histor-
ically been provided separately by the tra-
ditional DC positive and negative wiring
connections to each piece of gear, along
with grounding connections for some
equipment. This concept is changing rap-
idly, however, and in fact, both SmartCraft
and NMEA 2000 network cables are also
used for power distribution. - Confirm power delivery through the com-
mon power distribution/data delivery cable
harness. This is relevant if an NMEA
2000 network is being used to supply
low-current power to the connected
equipment in addition to transferring data.
The limit for power distribution under the
NMEA 2000 standard is 1 amp per device
connected, if needed. For devices requiring
more than 1 amp, auxiliary power supply
lines are required. The NMEA 2000
proprietary cables used in such a system are
available in two configurations, described
as heavy and light cable. The heavy cable is
intended for cumulative loads of up to
8 amps, and the light cable is designed to
handle cumulative loads of up to 4 amps.
Signs That Troubleshooting Is Necessary
Signs of problems with networked equipment
include dim screen displays and “scrambled”
or nonexistent data. If the equipment has a194 marine electronics installation and troubleshooting