Humminbird 900 Series Installation And Operation Manual page 128

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
The control head loses power at high
speeds.
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.
Possible Cause
If the power output of your boat's engine is unregulated, the control head may be protecting itself using
its over-voltage protection feature. Make sure the input voltage does not exceed 20 Volts.
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 boats engine may be interfering with sonar reception. See Finding the Cause
of Noise for more information.
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