Simrad J300X autopilot repair: fault found and corrected
A reliable autopilot is essential for safe passage making, crew comfort and precise course keeping. In this service case, we were called to diagnose a Simrad J300X autopilot that would turn correctly to starboard but failed when commanded to port. Each attempt to steer to port produced an overcurrent condition and blew the fuse, a strong indication of a possible short circuit or fault in the drive-control circuit.
Symptoms reported on board
- The autopilot responded in only one steering direction.
- Port commands caused excessive current draw.
- The protection fuse failed repeatedly during operation.
- The issue made the autopilot unreliable for navigation and watchkeeping.
Diagnostic process
We attended the vessel, removed the J300X control unit and transferred it to our specialist workshop for controlled testing. This approach allows the electronics to be checked safely without risking further damage to the vessel’s steering system, power supply or cabling.
During bench testing, we reproduced the fault, traced the abnormal current draw and identified the source of the failure. Once the defective section was located, the unit was repaired and prepared for reinstallation.
Reinstallation and sea-readiness checks
After the repair, the Simrad J300X was reinstalled on board and tested in both steering directions. Final checks confirmed correct operation to port and starboard, stable current behaviour and reliable response from the autopilot system.
Why this type of fault should not be ignored
An autopilot that blows fuses or works in only one direction should be taken out of service until properly diagnosed. Replacing fuses repeatedly without finding the cause can damage control electronics, wiring, relays or the drive unit. Early diagnosis helps protect the installation and restores confidence before the next passage.
Useful documentation
If your autopilot, plotter or marine navigation electronics are showing intermittent faults, abnormal current draw or steering-control problems, contact us for professional inspection and repair.