Humminbird 425 SX User manual

OPERATIONS
MANUAL

THANK YOU FOR CHOOSING YOUR 425SX FISHFINDER, MADE BY
TECHSONIC INDUSTRIES, MANUFACTURER OF AMERICA’S #1 NAME IN
FISHFINDERS, HUMMINBIRD. HUMMINBIRD HAS BUILT ITS REPUTATION
BY DESIGNING AND MANUFACTURING TOP QUALITY, THOROUGHLY
RELIABLE MARINE EQUIPMENT. YOUR HUMMINBIRD PRODUCT IS
DESIGNED FOR TROUBLE-FREE USE IN EVEN THE HARSHEST MARINE
ENVIRONMENT.
IN THE UNLIKELY EVENT THAT YOUR HUMMINBIRD DOES REQUIRE
REPAIRS, WE OFFER AN EXCLUSIVE SERVICE GUARANTEE. COMPLETE
DETAILS ARE INCLUDED AT THE END OF THIS MANUAL.
WE ENCOURAGE YOU TO READ THIS OPERATIONS MANUAL CAREFULLY
IN ORDER TO GET FULL BENEFIT FROM ALL THE FEATURES AND USES OF
YOUR HUMMINBIRD PRODUCT.
WARNING! THIS DEVICE SHOULD NOT BE USED AS A
NAVIGATIONAL AID TO PREVENT COLLISION, GROUNDING,
BOAT DAMAGE, OR PERSONAL INJURY. WHEN THE BOAT IS
MOVING, WATER DEPTH MAY CHANGE TOO QUICKLY TO
ALLOW TIME FOR YOU TO REACT. ALWAYS OPERATE THE BOAT
AT VERY SLOW SPEEDS IF YOU SUSPECT SHALLOW WATER OR
SUBMERGED OBJECTS.
THANK YOU

Section 1: Installation preparation . . . . . . . . . . . . . . . . . . . 2
Parts Supplied . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Installation Overview . . . . . . . . . . . . . . . . . . . . . . . . . 2
Alternative Transducers and Mounting Methods. . . . . . 4
Beginning Installation . . . . . . . . . . . . . . . . . . . . . . . . . 5
Section 2: USING THE 425SX. . . . . . . . . . . . . . . . . . . . . . . 6
How Sonar Works . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Simulator Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 6
What You See On Screen . . . . . . . . . . . . . . . . . . . 7–12
Control Functions . . . . . . . . . . . . . . . . . . . . . . . . 12–15
Menu Functions . . . . . . . . . . . . . . . . . . . . . . . . . 15–25
Section 3: ADVANCED FEATURES. . . . . . . . . . . . . . . . . . . 25
Using Diagnostic . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Section 5: MAINTENANCE . . . . . . . . . . . . . . . . . . . . . . . . 27
Maintenance and Troubleshooting . . . . . . . . . . . . 27–30
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
TABLE OF CONTENTS

2
INSTALLATION PREPARATION
PARTS SUPPLIED
PARTS SUPPLIED
Before installing your 425SX, please ensure the following parts are included in
the box:
•425SX fishfinder
• Transducer with 6m (20') of cable and mounting hardware kit
• Mounting system and mounting hardware kit
• 2m (6' ) power cable
• Publications kit
Note: The 425SX+includes speed and temperature sensors with
appropriate hardware and instructions for installation.
If any of these items are missing contact your local dealer.
ACCESSORIES
Humminbird offers a wide assortment of accessories that complement and
expand the capability of your new 425SX. These accessories are designed with
the same high standards. The Humminbird Accessory catalog included with
your unit contains descriptions of the many accessories available and ordering
information. All Humminbird accessories are available through your full-service
Humminbird dealer.
INSTALLATION OVERVIEW
The 425SX consists of two primary components to install: the control head and
the transducer.
The control head contains the sonar transmit and receive circuitry, as well as the
user controls and display. It should be installed in a location that provides access
to the controls and visibility while in use. The control head mounts on a quick
disconnect mounting system that swivels and tilts, providing flexibility for
viewing from almost anywhere on the boat.

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INSTALLATION PREPARATION
INSTALLATION OVERVIEW
The transducer converts electrical energy from the transmitter into mechanical
pulses or sound waves. The transducer also receives the reflected sound waves
and converts them back into electrical signals for display on the control head. It
should be installed in contact with the surface of the water in an area that has
smooth water flow - usually on the transom of the boat. There are several
mounting options for the transducer. Review
the following section to determine the
method that works for you and your boat.
Determining How to Mount the
Transducer
The 425SX includes a model XT-6-24
transducer. This transducer can be mounted
on the transom of the boat, or bonded to
the inside of a fiberglass hull boat.
The transom installation, which is the most
widely used, places the transducer on the
outside of the boat hull. This technique
produces the least signal loss, and provides a
way to adjust the transducer after
installation. The mounting hardware
included is designed to protect both
the boat and the transducer should the
boat strike debris in the water or when
trailering.
As an alternative to transom mounting,
it is possible on many fiberglass-hulled
boats to glue the transducer on the
inside of the boat hull. Since fiberglass
has similar sonar characteristics as
water, the sonar signal can pass
through the boat hull with minimal
loss. The hull of the boat must be single
layer construction (not double-hulled).
Also, any air trapped in the lamination
of the fiberglass would prevent the sonar
Transom Mounted Transducer
Inside the Hull Mounted Transducer

4
signal from passing through.
Inside the hull installations require no holes to be drilled into the boat and
through experimentation, high-speed operation comparable to transom
mounting can be achieved. Two part, slow cure epoxy is required to glue the
transducer in place.
ALTERNATE TRANSDUCERS AND MOUNTING METHODS
The 425SX comes with everything necessary for installation and operation on
most boats. However, there are several situations which may require a different
type of transducer. Inboard boats, wood or metal hulls, and sail boats create
unique transducer mounting needs. Alternate transducers and mounting
methods are detailed below.
Portable Mounting
The standard transducer can be adapted for
portable installations using part number MHX-PT2.
This accessory adapts your transducer to a suction
cup mount for temporary installation on the boat
hull or other surface.
Trolling Motor Mounting
The standard transducer can also be adapted to
mount on most trolling motors using part number
AD-STM-7. This accessory includes a bracket and
hose clamp that allows mounting the transducer to
the body of most trolling motors.
TRANSDUCER EXCHANGE
Other transducers are available as replacements for the standard transducer.
You may exchange your new and unassembled transducer for another type by
returning it to the address listed in Customer Support. Some transducers may
have additional costs. Refer to the Accessory catalog or call Customer Support
for information.
INSTALLATION PREPARATION
ALTERNATE TRANSDUCERS AND MOUNTING METHODS

BEGINNING INSTALLATION
Now that you have determined the transducer mounting method, you can
begin installation of the 425SX. The fold out installation guide included
provides detailed step by step instructions for installation of the control head
and transducer. For transom mount transducer installations, you will need the
mounting template at the back of this manual.
In addition to the parts included you need the following for installation and
operation:
• A powered hand drill and various drill bits
• Phillips and flat-head screw drivers
• A ruler or measuring tape
• Pen or pencil
• 12 volt power source (your boat’s battery)
• A 1-amp fuse
• A fuse holder (if you are wiring directly to the boat’s battery)
• Silicone sealant (for sealing drilled holes)
• 2-part, slow-cure epoxy (for inside the hull transducer installations)
INSTALLATION PREPARATION
BEGINNING INSTALLATION
5
Note: If you have purchased the 425SX+you will have in addition
to the parts and instructions above:
• Speed and Temperature sensors
• Instructions for installing speed and temperature sensors
• Appropriate hardware to mount sensors

USING THE 425SX
HOW SONAR WORKS
6
HOW SONAR WORKS
Your Humminbird unit uses sonar to
locate and define underwater objects,
define the bottom terrain, as well as
determine distance.
Sonar technology is based on sound
waves. Your Humminbird unit sends out
a sound wave signal. With this signal it
determines distance by measuring the
time between the transmission of the
sound wave and when the sound wave
is reflected off an object. Your
Humminbird uses the reflected signal to
interpret location, size and composition of an object.
Sonar is very fast. A sound wave can travel from the surface to a depth of 70m
(240') and back again in less than ¹⁄₄ of a second. It is unlikely that your boat
can "outrun" this sonar signal.
The 425SX is a 200 kHz, single-beam fishfinder. The 200 kHz frequency
provides excellent sonar resolution (the ability to distinguish small returns or
returns which are close to the bottom), while providing depth capabilities to
185m (600’). The shape of the sonar beam is symmetrical and covers an area
of approximately 24 degrees side to side and front to rear.
Actual depth capability depends on factors such as bottom hardness, water
conditions, and transducer installation. Units will typically read to deeper
depths in fresh water than in salt water.
SIMULATOR OPERATION
The 425SX contains a simulator that allows you to use the unit as if you are on the
water. The simulator is invaluable for learning how to operate the 425SX.
There are two ways to start the simulator. If the unit is powered off, press and hold
the POWER button for approximately three seconds until you hear a continuous chirp.

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USING THE 425SX
SIMULATOR OPERATION
The simulator can also be started by selecting
the Simulator option on the start-up screen
after you power-up the unit. When this
screen is shown, simply press the DOWN
ARROW until “Simulator” is highlighted.
When the screen times out, the unit will be
in simulator mode.
When in simulator operation, the 425SX responds to control inputs as if it is in
actual operation, so feel free to experiment, or to customize the unit for your
particular operation.
To exit Simulator mode, power the unit off.
FEATURE MEMORY
If your 425SX is installed with a transducer connected, any changes you make
to the set-up or User Options (see Control Functions) while in Simulator are
retained in the unit’s memory. This allows you to use simulator to experiment
with the various set-up options, and retain your selected settings for normal
operation.
If you are using the 425SX in Simulator when no transducer is connected, any
selected options are lost when the unit is powered off. The 425SX will return
to Factory Settings, or options selected when last used with a transducer, if no
transducer is connected.
IMPORTANT: A transducer must be connected to the 425SX in
order to retain user settings selected when in simulator mode. If
no transducer is detected, the unit defaults to pre-selected
options when powered off.
What You See On-Screen
Your 425SX uses a 160 x 160 matrix FSTN LCD display. This display provides
outstanding viewability in all light conditions over a wide range of
temperatures.

At initial power-up, the 425SX uses settings that were set at the factory. After
initial use, the 425SX will remember the settings you enter.
There are several elements on-screen that are common to all modes of
operation.
Temperature/Speed. The
initial screen layout takes one
of two basic forms depending
on whether the optional
Temp/Speed accessory is
installed. Figure A shows the
default view when the
Temp/Speed accessory is
installed. Figure B shows the
default view when the
Temp/Speed accessory is not
installed.
Depth. The digital depth
number shows the water
depth directly beneath the
transducer location.
Depth Range. The depth range
is shown to the right of the screen.
The upper number is 0 indicating
the surface of the water. The lower
number is one of the nine depth
ranges available that best match
the depth of the water. As the
depth of the water changes, the
range changes as necessary in
order to retain a bottom
representation on-screen.
8
Bottom Depiction
USING THE 425SX
WHAT YOU SEE ON-SCREEN
Figure B
6
Zero Line
Figure A
Water Depth Depth Range