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Troubleshooting your marine electronics


Marine electronics are very reliable as long as they have power, data and the correct settings. 

Problems are rare, but if they happen, a systematic inspection of the basics may well identify the problem and avoid the need to call in a qualified technician or the annoyance of losing time on the water.


It’s possible that what you assume is a fault may be a misunderstanding of how your systems work. In the heat of the moment, things can get forgotten or missed.

Even if there is a deeper problem, checking through the basics will enable you to provide more detail to anyone assisting, which may lead to a faster resolution.


Here is a practical checklist of the critical areas to inspect if you find an issue when first powering up your electronics or if they fail when out on the water.

First steps


Is the whole system down? Then:


1 - Ensure the battery master switches are on, your boat is powered up correctly with other circuits responding as you would expect, and the controls or breakers for the marine electronics are on. Note switches may work in the reverse way to expected.


2 - Inspect the breaker panel or any fuses. Cycle the breaker off and on and check the condition of any fuses on the supply lines to the equipment – they can break down or become corroded with age. Keep spare fuses of the right type and rating somewhere handy.


3 - Use a multimeter to detect if you have power on the system. Larger boats may have a mix of power supplies with 24V to some elements of the system and 12V to items like VHF radios. A voltage converter may provide the 12V on a 24V boat, another potential point of failure to check.


Assuming you have power, or if only a single unit is causing a problem

4 - Check the brightness control on screens. A setting that works well at night may look like a blank screen in the daytime.


5 - Visually inspect all power connections on any non-working electronics to ensure they are in good condition with no fraying of the insulation, cuts, burns or corrosion to compromise performance. If the copper of the power cable is blackened, then remake the connection, cutting the cable back to untainted copper.


6 - Power cycle any inactive unit by turning it off and on again – this will reset any internal computer and may well also trigger an audible response to confirm the unit is responding in some way.

7 - If the failed unit shares data with the rest of the marine electronics, try disconnecting it from all other equipment, except for power and then see if it responds. Isolating it will rule out any issue caused by faulty data cabling or corrupted data.


8 - If all else fails, make a note of exactly which unit has failed, what you have observed when testing it and then call a local marine electronics expert. They may well suggest some additional checks to make appropriate to what equipment you have and what you have found.

Depth sounder and fishfinder issues


If the unit has power and is operating, but you do not see a depth reading or the fish finder screen is not showing even a primary readout of depth:


1 - Are you in deep water or turbulent flow, such as caused by following closely behind another boat? Losing your depth reading in these circumstances may well be expected due to the inability of the sonar pulse to reflect and provide a reading.


2 - Is the in-hull transducer heavily fouled or transom-mounted transducer in position correctly and undamaged. Inspect if you can.


3 - Check the transducer’s connections are secure and free of any damage or interference.


4 - If you experience an intermittent interruption of the sounder display and don’t think this is due to an issue with the power supply, check for possible radio-frequency interference by systematically turning devices on and off to identify a localised problem.


5 - If your transducer is mounted inside the hull in an oil bath without a skin fitting, check the fluid level in the transducer housing and top up if required.

6 - For dual-frequency fishfinders, ensure you use the proper frequency (200kHz for shallow water, 50kHz for 600-plus feet / 180-plus metres).


7. If your fish finder screen is not detecting fish and other targets, ensure the unit is not in auto mode and adjust the gain settings to suit the conditions until the screen becomes clearer.


8. If your fishfinder displays a second seabed reading between the surface and the actual bottom, this is likely caused by the hard edge where cooler water and warm water meet – known as a thermocline. You can remove this false bottom by adjusting the gain settings to a lower level

Chartplotter issues


If the unit has power and is operating, but you do not see the boat’s position, other expected data or a chart in the level of detail expected:


1 - Inspect the GPS antenna and the cabling and connections between it and the chartplotter (see also our more in-depth guide as to fundamental causes of positional data failure here


2. Ensure any data connection into the unit is plugged in correctly with no sign of corrosion on the plug or socket.



3. Check for interference from other electronic instruments by systematically turning each unit on and off. Also, run that check with any LED lighting you have onboard and any laptop power supply.


4. If the chart is not showing very much detail, ensure you have the correct charts loaded for your area. Zoom in at an appropriate scale and check that any menu options are correctly set for the required level of detail.


5. If your charts are not loading correctly, ensure any chart card used is clean, free from damage and properly inserted.

Radar issues


If your radar powers up but does not paint a picture:


1 - Ensure the radar is in transmit (Tx) mode.


2. Check that the open scan antenna is rotating or that you can hear the hum of a closed radome’s antenna turning (without getting closer than the manufacturer’s recommendations). If you suspect the antenna is not working, power down and check its general condition only within the manufacturer’s recommended safety practices. Ensure the cable and its connections are sound.


3. Check the settings and work through our advice here which applies specifically to Simrad® radars but has lots of good general guidance applicable to all makes

Autopilot issues


If your autopilot fails to hold a course, fails to work in Nav Mode or steers abruptly or hesitatingly, there are basic checks you can make:


1 - Double check the autopilot is in your intended mode, either auto (following a course you manually set) or track (following a route)


2 - Ensure the steering pump or ram is responding to your manual inputs. With engine(s) off on the berth, you will usually hear it react to commands.


For hydraulic steering systems, ensure the ram or pump moves the rudder(s) or drive(s) and check for low hydraulic level, leaks or airlocks.


3 - Ensure that the unit providing heading information (usually a fluxgate compass on older units or a GPS compass in more modern autopilots) is connected and producing heading information on your electronics.



4 – If the heading information is wildly inaccurate and not consistent, check that no one has placed any metal objects close to the location of your autopilot’s compass (which is often installed in a locker or behind seating below decks) or that the compass itself is undamaged. Consider running the recommended recalibration routine if there is no apparent reason for the issue.


5. Fine-tune any manual gain settings if the autopilot is wandering and not holding a course very well. If you see no improvement and are satisfied that the autopilot is getting good heading information and its steering equipment is working, consider recalibration.


6. If the autopilot does not respond to commands to follow a chartplotter track, check its data connections.


For general advice on selecting an autopilot, download the Simrad® Autopilot Buyers Guide here.

VHF issues


If your radio has broken or weak transmission, then follow our guide to this subject –


Safety first


Safety first is the rule when performing marine electronics inspections and fault-finding. Boats were constructed in lots of different ways over the years. Low voltage circuits should have been installed away from any high voltage power with any electrical connections protected, but when fault-finding 12V/24V circuits, you may find 110V/220V circuits close by. Great care needs to be taken, particularly if uncertain of your abilities or need to reach behind a panel without seeing your hand. It’s always a good idea to disconnect any shorepower, inverter and generator power whenever there is a risk of this kind.


Ensure you are adequately insulated from electrical currents and follow instructions on your multimeter. Be careful not to create the likelihood of a short circuit (where a positive cable can touch a negative one or the boat’s ground) as that will create a risk of fire for the vessel and a burn for you, even on 12V circuits. Do also follow any specific manufacturer’s safety instructions, particularly for radar.

Further assistance


If you decide you need help, or the job requires professional assistance, do take the advice of your Simrad® dealer, marina technician or systems provider. They will have the right experience and kit to assist with a diagnosis and fix.