[TG] [TG11] diagnosing issue with ST4000 wheel autopilot

[Tom - Raymarine - Moderator]

Hello Laurent,

- After the problem occurs and you go to Standby, in what way does the pilot act weird? Just shows 4001, or other stuff, and if so, what?
- Does the unexpected turn always happen to starboard?
- How do you get it working again - power cycle?

Normally, when a pilot goes hard-over one way after working successfully for a time, it's either:
- broken winding in the fluxgate compass, making and breaking contact intermittently; when broken, you'll get a 'dead sector' of static heading. Next time the problem occurs, see if you can steer slow circles and watch the indicated pilot heading (on the pilot display or a repeater, e.g. chartplotter) and see whether it turns smoothly, consistently and evenly throughout - if not, your fluxgate is suspect.
- a dead spot on the rudder-reference, if there is one, which is intermittently causing the pilot to think that the helm is hard port, causing it to drive starboard to correct.

The '4001' display sounds like either an internal fault (non-repairable...) or marginal power-supply causing the 4000's CPU to brown out, either of which could well be triggered by the extra load caused by the helm driving rapidly hard-over, perhaps because of a rudder-reference fault.

Perhaps a video of the behaviour might help, if you can coax it to happen again at the right time. Other than that, you can either work through the above or it might be time to consider a new pilot.
Regards,
Tom