[DG] [DG11] Wheel Pilot error.

[russ_stuart]

My system has developed a problem whereby the readout on the wheel pilot differs from that on the ships compass, thereby rendering the Autohelm unusable.
The difference (bearing offset) resembles a deviation curve (see attached spreadsheet) from no difference to about twenty degrees out (+ve), back through no error and on to 20 degrees out (-ve).
I have tried, several times, to recalibrate the Wheel Pilot (Autohelm)
I have checked the ships compass against a hand held.
I have checked that there is nothing near the fluxgate compass that could influence it.
I have disconnected the fluxgate from the instrument and measured the resistance across the various pairs as described on the Raymarine fault finding notes and all are well within tolerance.
Its a Seatalk1 system ST4000+ and Fluxgate plus several other instruments.
Any help would be much appreciated.