Lose arm on tillerpilot

[Arrandir]

I have a tillerpilot, an Autohelm ST2000, which got a problem. The arm which moves in and out is lose. It's possible to move it in and out by hand, but the electrical motor inside the tillerpilot can't move it.
I tried to take the parts from each other to see what's wrong, but can only dissemble it into two pieces. Do any one know how to dissemble the tillerpilot or have any ideas how to fix it? I have tried to turn the arm around and hoped that was the way to put it back in position, but it did not work.