From DIY Boat Owner Magazine
When your depth sounder or fish finder isn’t up to par, these procedures will help you make a diagnosis
By John Payne
odern electronics have
the performance and
reliability of depth
sounders and fish
finders, but sometimes they do fail. The
power output of a depth sounder unit
is important with respect to the range
and resolution of the unit. The higher
the output power, the greater the depth
range and signal return. Depth transducers are normally constructed of a crystal
composed of various elements and it’s the
crystal, or a piezoelectric element, that
converts an electrical signal to an acoustic
signal. Never shake or strike the transducer as it could damage
The majority of depth sounders operate at a frequency of
200 kHz. Acoustic signals are
affected by seawater and bottom formations, as well as
biological material (algae and
plankton) and suspended
particulates (silt, dissolved
minerals and salts), along
with water density,
salinity and temperature. Before troubleshooting, read the
manual. Verify that
the settings are
correct, as straying fingers are a
common problem. Ensure
to auto or default to the factory settings.
For each problem below, if all else fails,
try a hard factory reset.
Problem: Malfunctioning Display
If the display has faded, is flashing
or just blacks out, follow the steps below.
If the display is foggy and shows signs of
condensation, the unit requires servicing.
1 Electrical system checks: Verify that
the battery supply voltage is normal,
around 12 volts. If it’s too high when the
engine is running, there might be an alternator regulator problem.
It’s common to see displays black
out if the sounder is connected to an
engine start battery. Start the engine and
there may be a voltage surge or a dip.
Connection problems are a major cause
of voltage drops and this can be at the
distribution panel or at the battery. Use
a multimeter to check the voltage level at
the depth sounder plug with the engine
both on and off. If the voltage level at
the battery is much higher than at the
sounder, then there’s likely a connection
Check that all power supply connections are properly coupled, are tight and
the plug’s pins are straight with no sign of
corrosion. Check both the fuse and fuse
holder for any signs of corrosion. If the
unit is supplied from a circuit breaker,
check the terminations at the breaker and
also operate the breaker several times.
2. Interference tests: Checking for electrical interference initially means turning off
all other electrical equipment. In many
cases, interference is caused by the engine,
in particular outboard engine ignition systems and charging systems. Power down
all other systems and then progressively
start up the engine and, one at a time,
turn on the other equipment to determine
the interference source. If interference still
remains when all other systems are off, the
depth sounder may have a malfunction-
ing automatic noise rejection function. In
some cases, when you have done everything to eliminate interference sources, you
need to run the power supply through a
noise suppression unit.
Always ensure that cables are installed
well clear of heavy current-carrying cables.
Never install sounder cables next to speed
log cables, as the interference problem
can be significant. Interference may also
be due to cavitation (see below).
3. Cavitation checks: Cavitation is caused
by water turbulence passing over a sounder
transducer head and can significantly affect
transducer performance. At slow speeds,
water flow is relatively smooth. When the
boat starts to travel at speed, air bubbles
are created over the face of the transducer.
Transmitted signals reflect back off the air
bubbles, and this causes noise and masks the
acoustic signals. Underwater turbulence is
caused by the boat’s hull form or underwater
obstructions, as well as the actual water flow
over the transducer, and from propulsion.
Transom-mounted transducer units
must be properly sited and mounted to
avoid turbulence. Transducer installation
is crucial and it must be installed in areas
of minimal turbulence or well clear of the
main hull flow areas.
If you’ve done a factory reset and
all of these actions fail, you may need an
Problem: Power, No Display
If the depth sounder powers up but
there’s no display, there are four elements
1. Perform the basic electrical system
2. Inspect the connectors and pins of
the display unit and the transducer,
checking for corrosion. Check that both
the connectors and connector pins are
straight. Use caution when straightening
a bent pin as they are relatively brittle.
Connectors are often not inserted prop-