Unpredictable heading change

Hello,

I recently had troubles with my Navpilot 511 : unpredictably in AUTO mode, it generates itself a change of the heading set point. (For example, from a set point 350°, I suddenly found a new set point at 150°). Naturally, this shift causes an instant alarm "deviation alarm", and that's how I am warned (it beeps).

My system consists of an autopilot Furuno Navpilot 511, a Furuno GP32 GPS, a Furuno RD30 repeater and VHF. All these devices are connected to the same NMEA83 bus.

This happened twice (2 consecutive times) during a trip of 12 hours, and 2 days later with the same scheme (2 consecutive times) during a trip of 22 hours. In 2 cases, after the two consecutive anomalies, I turned off and on the device, and the problem does not happened until the arrival.

Has anyone heard about this and is there any diagnostic than can help me in solving my trouble.

Thank you for your help.
JF.

Auto mode really just involves the pilot and the heading compass. (holding a set course, based on the compass) It sounds like your compass is having a problem. When the having the problem, check the compass and see what the status light is doing.

OK, I think that a compass trouble could generate a large rudder shift and of cause a deviation alarm but I don't know this could make a heading set point change on the autopilot. I am sure to have seen this value change in the top left cell of the display as if the knob was rotated very quickly or something was sent by a remote device on the network.

If it seems to be control related, I would recommend ensuring any pilot display has either a cable or terminator connected to the connectors at the back of the display. There never should be an open connector or rubber cap. I have run into many improperly terminated control heads when dealing with autopilots. A bad control bus will cause many unpredictable problems.

Thank you Johnny for your reply.
I just have a look on my display (FAP5011) and I saw that the bus terminator was missing.
I refound it in a box and plugged it now.
Do you think it could explain my trouble ?
Thank you for your feedback.

Yes, it is/was most likely the issue.
You should redo the rudder setup, rerun the rudder test, and seatrial (except for compass cal) and then try it.