transmitted. You must make an airtight, void-
free bond between the transducer face and the
hull surface. Use a glob of silicone caulk or
3M 4200 adhesive sealant, being sure to use a
sufficient amount of the adhesive to create a
solid mass of material between the entire face
of the transducer and the hull. Do not use3M
5200 for this purpose, or you will have a very
difficult time removing the transducer when
you want to replace it.Installation and Troubleshooting
Now that we’ve determined the location and
method of mounting the transducer, let’s
move on to installation and troubleshooting.Cables
As noted earlier, the cable is impedance
matched to the system and altering its length
will affect system performance. Route cables
so as to avoid EMI and sharp bends.
Intermittent problems with depth sounders
are often related to cable failures. A “wiggle”
test of the entire length of cable will help you
identify loose or broken connections under the
cable insulation.
To perform a wiggle test (which will work
on any long cable runs):1 Run the system while flexing the cable
itself, particularly its termination points.
2 Have a partner watch the display and see
if it remains constant.
3 If the display blinks out while you’re wig-
gling at a certain point, you have found a
bad connection or break in the wire(s).In most cases, repair will require replacing
the cable with a factory-supplied unit. In other
units, the cable may be permanently con-
nected to the transducer, so replacing the
entire transducer/cable assembly may be your
only option.Warning: Never disconnect the cable
from the display while the system is turned
on; it can produce a pronounced electrical
arc. Power down the unit before discon-
necting the transducer cable.Power Supply
Depth sounders are quite sensitive to power sup-
ply. Most operate in the 10 V to 16 V range and
require 1 to 4 amps of current. Symptoms of
excessively high or low voltage vary with the com-
plexity of the unit. With a simple numerical read-
out sounder, you’ll encounter errors in depth
readings or a blinking display; with a fishfinder,
you’ll get garbled and shifting or random bottom
contours. The obvious troubleshooting approach
is to test and confirm voltage supply to the dis-
play unit with your DVOM.Interference
As with all electronics, you must also be aware
of the possibility of interference. In spite of
cable shielding, cross-conductor interference
often occurs, especially on modern boats in
which numerous cables are crowded together
in conduits or wire trays. Because the cable
connecting the transducer to the display is a
fixed length, flake excess cabling in an out-of-
the-way location (see Chapter 14). However, if
you must coil the cable, be sure to locate the
coil far from any of the high-output emitters
identified in Chapter 9.
If you suspect interference (after first con-
firming the quality of the voltage supply and
return ground to the system), the only way to
isolate the source is through process of elimi-
nation: With everything else on the boat
turned off, including the engines, check the
depth sounder for normal operation. Then,
turn on one circuit at a time and see if the prob-
lem appears. After you’ve isolated the culprit,
establish an appropriate zone of separation
between the offending component or circuit
and the transducer cabling, as described in160 marine electronics installation and troubleshooting