Marine electronics fail in a narrow set of ways, and the causes are physical far more often than electronic. Working through them in order finds most faults before anybody needs to attend.
One boundary first: anything forming part of GMDSS or other regulated safety equipment must be left to approved engineers. That equipment is subject to survey and type approval, and work on it by anybody else is not appropriate regardless of competence.
Start with power
The cause of the majority of faults, and the one most often skipped because the equipment appears to have power.
Voltage at the unit, not at the battery
Measure at the equipment's terminals, with the equipment switched on and drawing current. Voltage drop over a long run, through corroded connections or undersized cable, can leave a unit well below its operating range while the battery reads fine.
Many symptoms attributed to failing electronics — resets, freezes, refusing to start — are low voltage under load.
Check it under load, not at rest
A connection can measure correctly at rest and collapse when current flows. If the fault appears when the engine starts, the windlass runs or another load switches on, that is the signature.
The earth is half the circuit
Earth faults produce some of the strangest behaviour: instruments reading incorrectly, equipment working only when something else is switched on, interference that comes and goes.
Check earth connections as carefully as positive ones. They corrode just as readily and are inspected far less.
Fuses
Check them, and check the holders. Corroded fuse holders are a common intermittent fault, and a fuse can look perfectly good while making poor contact.
Then connections
Vibration, salt and moisture work continuously on every connection aboard.
Look for the green. Corrosion is visible and it is the leading physical cause of failure. Terminals, plugs, the backs of connectors, and anywhere water can sit.
Check tightness. Vibration loosens things over a season.
Disconnect and reconnect. A partially corroded connection can be restored by disturbing it, which is diagnostically useful even when it is not a permanent fix. If reseating a connector fixes the fault, you have found the area.
Look where the cable enters. Water tracks along cables and enters at the gland or the connector. Damage is often at the entry point rather than along the run.
Check the aerial connections particularly. Exposed, high up, and rarely inspected until something stops working.
Intermittent faults are physical almost every time. Electronics tend to work or not; connections work sometimes.
Then interference
If equipment works until something else is switched on, you have an interference or a supply problem.
Common sources: inverters, battery chargers, LED lighting of poor quality, pumps and motors, and equipment sharing a supply with something noisy.
Diagnosis is straightforward: switch everything off, confirm the fault disappears, then switch things on one at a time until it returns.
Poor-quality LED lighting is a frequent and under-recognised culprit, particularly affecting VHF and radio reception.
Then the data
On modern instrument networks, a great deal of odd behaviour is data rather than hardware.
Check that the network is terminated correctly at both ends and powered as it should be. Check that the source of each piece of data is what you expect — where two devices supply the same information, displays may be showing the wrong one. Check that firmware versions across the network are compatible, because a mismatch after an update to one device can produce peculiar results.
A network fault often shows as several instruments misbehaving together, which is a useful signature: one instrument wrong is that instrument, several wrong is the network.
When to stop
Stop and call an approved engineer when the fault involves:
- Any GMDSS or regulated safety equipment
- Anything subject to survey
- Anything requiring the unit to be opened
- Anything where a mistake would compromise safety equipment
Also stop when you have found the area but not the fault. An engineer arriving with "it is somewhere in the run between the panel and the masthead, and the voltage at the unit is 11.2 volts under load" will resolve it far faster than one arriving with "it does not work".
Prevention
Annual inspection of connections, cleaning and protecting anything showing corrosion. Cable runs supported properly so vibration does not work at the terminations. Appropriately rated equipment where exposure is possible. And a record of what is installed, where it is powered from, and what was done to it — because the next fault is easier to diagnose with a history.
Spares aboard matter more than they do ashore: fuses of every rating, connectors, contact cleaner, self-amalgamating tape, a multimeter, and a spare unit for anything you could not manage without.
Our team's background includes marine electronics and GMDSS-certified radio operation alongside business IT. Start a conversation if you need vessel systems supported by people who understand both sides.
