Humminbird 727 - Manual (Page 80)

75
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
The boat’s engine
Cavitation from the boat’s
propeller
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.
531524-1_A - 717 & 727 Man_Eng.qxp 9/30/2006 7:24 PM Page 80