Couldbe any number of things.
feedback could be dead yet the dirve unit could be fine. The course computer needs to get rubber feedback as well as compass
feedback to determine how much rudder its required. A call to increase rudder without getting rudder feedback could be either end of the problem OR be the course computer telling you it's not getting anything. You need to validate the parts
before you can rule
out what it is and is not.
1. Can you do a dockside calibration.
2. Can you do a sea trial calibration.
Just because you did it a long time ago it can be a good apporach to finding the real problem before you start throwing money
around. Validate what it is not and go from there. You can disconnect the fluxgate
and rotate it through 90 degree arcs in the slip to validate the compass
is working. These are easy things anyone could do and get more details.