Raymarine Autopilot Problem

[johnmurray]

I have a Raymarine ST6001 autopilot in my boat that was installed by the dealer ten years ago when I purchased the boat. Given the way I use the boat, the autopilot has been used for steering only, not setting waypoints or interconnections with my chartplotter, etc. The autopilot worked as it should for the first nine years, but last season it would no longer hold a course and would turn the boat without notice. I checked for any mechanical issues like the rudder hook-up but everything appeared sound. I then tried the re-calibration procedures as per the manual but that didn't make any difference.
Does any one have any suggestions as to what the problem might be and how to correct it? If it is not easily fixed, given the age of the device, it is likely obsolete and not worth a professional repair. If that is the case, any suggestions for a replacement?

[Russell]

Have you installed any wiring or electronic devices near the fluxgate compass head. I had a similar experience many years ago when the wires for the water pump were next to the fluxgate compass head. My wife turned on the galley sink and the boat did a 90 degree turn from the magnetic field given out from the current in the wires. Relocating the compass head solved the problem.

[TimQ]

check your rudder reference unit. Your description fits with a failing unit.
remove the wires at the course computer and test resistance as someone turns the wheel for you from lock to lock.
green to red 5,000 ohms
green to blue 0 to 5000 ohms for 360 degrees of rotation ( you will most likely see something closer to 2,000 to 3,300 ohms)
If you get something close to these readings it's OK. If there are any discontinuities in the readings that is also a sign of a bad unit.

These are wound wire resistors that wear with use and eventually start performing irregularly before just failing altogether.