Humminbird 531338-1_C Cavitation from the boat’s, Isolation, propeller, The boat’s engine, Possible Source of Noise, Other electronic devices

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	Isolation
Other electronic devices	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.
The boat’s engine	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.
Cavitation from the boat’s	Turbulence created by the propeller can cause noise;
propeller	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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