My pen stopped working and since it is out of warranty, I figured that I have nothing to lose by taking it apart. So I did. I simply grasped the front end of the pen with pliers and unscrewed it from the barrel. I found the problem. I think it is due to bad engineering. The pen depends on a solid contact between a steel wire and the aluminum body of the pen. Over time, electrolysis causes corrosion between the two dissimilar metals and forms an insulator. I also discovered that the controller on this pen has an eraser capability. Here's an image of the whole thing. I filed back the barrel a bit, cleaned the contact area, and applied some electric contact grease before assembling the pen. It now works again!