Archive for August 9th, 2009

Kensington Expert Mouse Trackball: Scroll Ring Troubles

Trackball Scroll Ring

Trackball Scroll Ring

The oddly named Kensington “Expert Mouse” (it’s a trackball) sits to the left of my keyboard, where it serves as my main pointer controller; I’m right-handed, but have used a left-hand mouse / trackball for years.

Recently the scroll ring has become balky, stuttering upward & downward rather than actually scrolling. It’s an optical device, so I suspected it had ingested a wad of fuzz that blocked the beam path.

The top photo shows the infra-red emitter adjacent to the scroll ring’s slotted rim. The silver bar to the right of the emitter is the magnet that provides those soft detents. There’s no obvious fuzz.

Disassembly is straightforward.

  • Tip the ball out into your hand and put it where it can’t possibly roll off the desk.
  • Peel the four rubber feet off the bottom, remove four screws, and the top half of the body pops off.
  • Remove three screws from each of the two button cap assemblies and pry the button caps off the case bottom.
  • Remove two screws from the ball socket, pull it off, and clean any fuzz from the openings.

Surprisingly, I didn’t find much crud at all.

Scroll Ring Emitter and Detector

Scroll Ring Emitter and Detector

This photo shows the IR emitter and detector, peering at each other across the electrical isolation gap in the circuit board. Nothing obviously wrong here, either…

They both seem to be dual elements, which makes sense for a quadrature position encoder. Unfortunately, replacing them seems to be really difficult; they don’t look like stock items.

So I put it back together, plugged the USB cable in, restarted the X server (this being Xubuntu 8.10), and it pretty much works again.

Kensington replaced a previous Expert Mouse under warranty when one of the three minuscule red bearing balls that support the trackball went walkaround, but that gadget had been getting erratic, too.

I’m not sure what’s going on, but I have a bad feeling about this.

[Update: More troubles lead to some interesting pix and an insight. Maybe even a fix!]

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