How to Troubleshoot a Bottom Line Fish Finder

by Mike Schoonveld

Bottom Line Fish Finders are one of the top brands of recreational sonar equipment available for boaters and anglers. They have a time-proven track record of service and reliability but like any mechanical or electronic equipment, they can occasionally break, malfunction or stop working completely. If yours is acting up or not working at all, some simple troubleshooting may diagnose the problem and determine the action needed to get it repaired.

Check Power Supply

  1. Disconnect power wire plug from the rear of the unit.

  2. Attach ground wire of test light to negative terminal of battery, power panel or other metallic part which is grounded. Insert probe of test light into the plug. One of the holes is power, the other is ground. If neither side turns on the light in the tester, you've found the problem.

  3. Check the in-line fuse if there’s no power to the plug. Fuses can be visually checked but testing with a multi-meter on ohms setting is better. A burned-out fuse will register zero ohms when probes are touched to opposite ends of the fuse.

  4. Check all power wire connections for loose or broken wires. Check the ground wire connections, as well.

  5. Check voltage with multi-meter if test light shows plug has power. Set the meter to DC voltage. Any reading above 12V is satisfactory. Less than that and all wire connections will need to be checked for corrosion.

  6. Check plug and receptacle, in-line fuse holder, connection to battery or power panel for corrosion. Clean corroded connections, reconnect and retest.

Funky Screen Picture

  1. Disconnect the tranducer plug from the rear of the unit.

  2. Check for corrosion and clean if necessary.

  3. Examine transducer. If through-hull type, ensure it’s still firmly affixed to the bottom of the boat and with no visible cracks. With boat out of the water, visually inspect transom mounted tranducers to ensure they are still mounted rigidly, in the correct position and are clean of algae and debris. Correct any problems noted.

Final Checks

  1. Check as much wiring as possible if checking/cleaning power supply and tranducer tests fail to show a problem. Use flashlight to visually check wires for nicks or bare spots from the unit to the power supply and from the unit to the transducer.

  2. If you know of someone with the same unit which is working, connect your unit to your friend’s wiring to see if problems continue.

  3. Disassembling the unit is never a good idea. There's nothing inside you can repair. Send the unit to the manufacturer for repairs if troubleshooting wires and connections fails to reveal problem.

Items you will need

  • Flashlight
  • 12V test light
  • Electrical multi-meter


About the Author

Mike Schoonveld has been writing since 1989 with magazine credits including "Outdoor Life," "Fur-Fish-Game," "The Rotarian" and numerous regional publications. Schoonveld earned a Master Captain License from the Coast Guard. He holds a Bachelor of Science in wildlife science from Purdue University.

Photo Credits

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