[C320-list] Raymarine Autopilot ST4000+ problem

[Taylor Devlin]

Our 2003 C320 is fitted with the Raymarine Autohelm ST4000+ autopilot.  It has worked really well since we owned it  but this season is playing up.  When selecting Auto it maintains the heading ok, but when is starts to correct a heading change it over corrects and eventually has the wheel turning left and right through 30-50 degrees.  This worsens until Sby is selected. The functional checks at the dock work ok.  The response and rudder gain settings are the same as in previous years, and the belt appears to be tensioned correctly.  Any ideas?

Taylor Devlin 
Escape #938