Garmin GPSMAP 420s Manual

The Garmin GPSMAP 420s is a 4-inch waterproof marine chartplotter featuring a sunlight-readable color display, built-in worldwide basemap, preloaded BlueChart g2 coastal charts, support for NMEA 0183 and NMEA 2000 networks, sonar compatibility, and an intuitive user interface. Below are key sections for safety, features, installation, setup, operation, and troubleshooting.

Features at a Glance

Key components: 4-inch QVGA color TFT display, Waterproof housing (IPX7), Power/data cable, Mounting hardware, Preloaded BlueChart g2 coastal charts.

Installation

Unpack and inspect contents. Choose mounting location carefully.

1. Mount the unit: Use included bracket to mount on flat surface; ensure clear view and access.
2. Connect power: Route power cable to battery; connect red to positive (+), black to negative (-).
3. Connect data: Attach NMEA 0183 or NMEA 2000 cables if interfacing with other devices.
4. Connect transducer: Plug in transducer cable for sonar functionality.
5. Secure all cables: Use cable ties to prevent strain and water ingress.

WARNING! Ensure power is off during installation. Route cables away from moving parts and heat sources.

First-Time Setup

Power on unit; follow on-screen prompts.

1. Initial language: Select language (default ENGLISH).
2. Configure units: Set nautical/miles/kilometers, depth, temperature, and coordinate format.
3. Calibrate compass: Follow on-screen instructions if external sensor is connected.
4. Set time: Choose automatic GPS time or manual setting.
5. Configure alarms: Set anchor drag, arrival, and depth alarms as needed.

CAUTION! Perform initial setup in open sky for optimal GPS signal acquisition.

Specifications

• Display Size: 4 inches diagonal.
• Display Resolution: 320 x 240 pixels.
• Waterproof: IPX7 standard.
• Power Supply: 10-32 V DC.
• Waypoints: 500.
• Routes: 50 reversible.
• Track Log: 10,000 points, 20 saved tracks.
• Chart Compatibility: BlueChart g2, BlueChart g2 Vision, LakeVü g3.
• Sonar: Supports frequencies 50/77/200 kHz.
• Operating Temp: -15° to 55°C (5° to 131°F).

Controls and Settings

Access menus via PAGE and MENU buttons. Front Panel: POWER, PAGE, MENU, ENTER, ROCKER (up/down/left/right).

On-screen: Use rocker to navigate; ENTER to select; MENU to access options.

Main Pages: Chart, Sonar, Compass, Highway, Data. Settings: System (units, time, alarms), Navigation (route preferences), Sonar (frequency, range), Communications (NMEA settings). Chart Setup: Detail, Orientation, Tides, Currents.

Connecting Devices

NMEA 0183: Connect to compatible devices for data exchange. NMEA 2000: Connect to network for sensor data. Transducer: Plug into sonar port for depth/temperature.

1. Turn off power before connecting devices.
2. Match wire colors per wiring diagram in manual.
3. Seal connections with waterproof tape or heat shrink.
4. Configure NMEA sentences in Communications menu.

Tip: Use Garmin NMEA 2000 starter kit for easy network setup.

Navigation & Chartplotting

Supports waypoint, route, and track navigation.

1. Create waypoint: Press MARK at current location or use cursor to select point on chart.
2. Create route: MENU > Route > New Route, add waypoints in sequence.
3. Navigate: Select Go To for waypoint or Activate for route.
4. Follow track: Load saved track and navigate along it.
5. Chart details: Zoom in/out with rocker; adjust detail level in Chart Setup.
6. View tides/currents: Enable in Chart Setup if data available.
7. MOB (Man Overboard): Press and hold MARK key to mark MOB position and begin navigation back.

WARNING! Always verify chart data and use navigation as an aid; maintain proper lookout.

Sonar Features

Displays depth, water temperature, and bottom contour.

1. Access Sonar page: Press PAGE until Sonar page appears.
2. Adjust range: Use rocker to set depth range manually or choose Auto.
3. Change frequency: Select 50, 77, or 200 kHz for different detail and depth.
4. Set alarms: Configure shallow/deep water alarms in Sonar menu.
5. Interpret display: Solid bottom indicates hard bottom; fuzzy indicates soft.

Note: Sonar performance depends on transducer installation and water conditions.

Care & Maintenance

Use fresh water and mild soap to clean exterior. Do not use harsh chemicals or abrasives.

CAUTION! Ensure unit is powered off and disconnected before cleaning. Do not submerge connectors.

Regulatory Information

FCC Compliance: This device complies with part 15 of the FCC Rules. Operation is subject to conditions: (1) device may not cause harmful interference, (2) device must accept any interference received. Copyright © Garmin Ltd. or its subsidiaries. BlueChart and GPSMAP are trademarks of Garmin Ltd. For support, visit www.garmin.com/support or contact Garmin Product Support.

Troubleshooting

Reset: Hold PAGE + POWER during startup to reset to factory defaults (erases user data).

Service: Contact Garmin Product Support or authorized service center.