Humminbird 700 manual Display Problems, Finding the Cause of Noise

www..reelschel531427-1 C - 767_Man_mEng.aticqxd 10/25/2005..com10:30 AM Page 102

Display Problems

There are several main conditions or sources of possible interference that may cause problems with the quality of the information displayed on the control head. Look in the following table for some symptoms of display problems and possible solutions:

Problem	Possible Cause
The control head loses power	If the power output of your boat’s engine is
at high speeds.	unregulated, the control head may be protecting itself
	using its over-voltage protection feature. Make sure the
	input voltage does not exceed 20 Volts.

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

When the boat moves at higher speeds, the bottom disappears or suddenly weakens, or the display contains gaps.

There are no fish detected, even when you know they are in the water under the boat, or sonar readings seem weak or faulty.

The transducer position may need to be adjusted. A mix of air and water flowing around the transducer (cavitation) may be interfering with the interpretation of sonar data. See your Installation Guide for suggestions on adjusting the transducer position.

Electrical noise from the boat’s engine may be interfering with sonar reception. See Finding the Cause of Noise for more information.

Sonar readings may be affected if the transducer is not positioned correctly (i.e. mounted at an angle, not straight down), or there is some kind of mechanical interference, either because it is mounted inside a hull that is too thick for proper sonar transmission, the bond between the transducer and the hull is not airtight, or because the transducer is dirty. Check with your Installation Guide for guidance on re-positioning the transducer, and make sure the transducer is clean.

Low battery voltage may be affecting the power of signal transmission.

Electrical noise from the boat’s engine may be interfering with sonar reception. See Finding the Cause of Noise for more information.

	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.

93 94