Finding The Cause Of Noise - Humminbird 931C Installation And Operation Manual

93x_Man_531370-1_A - vs4.qxd 2/18/2005

FINDING THE CAUSE OF NOISE

Electrical noise usually affects the display with many black dots at high speeds, and high sensitivity readings. One or more of the following sources can cause noise or interference:
Possible Source of Noise
Other electronic devices
The boat's engine
Cavitation from the boat's propeller
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Isolation
Turn off any nearby electronic devices to see if the problem goes away, then turn them on one at a time to see if the
noise re-appears.
To determine whether the boat's engine is the source of the noise, increase the RPMs while the boat is in neutral and
stationary to see if the noise increases proportionately; if noise appears when you rev the engine, the problem could
be the spark plugs, alternator, or tachometer wiring. Replace the spark plugs with resistor plugs, install an alternator
filter, or route the control head power and transducer cables away from the engine wiring.
Turbulence created by the propeller can cause noise; make sure the transducer is mounted at least 15" (38 cm) from the
propeller, and that the water flows smoothly over the face of the transducer at all times.
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