Making a Stubborn Mouse Go Again

Brian Ketterling

(Editor's note: My Commodore-compatible Smart Mouse suddenly refused to go up and down,
although horizontal movement was OK. Brian provided this information in answer to a post on the
Internet, and it's repeated here for others who may have a similar problem.)

Flip the mouse over, remove the screw and take off the bottom plastic plate (gently, so the hooks at the
top don't break).  Set the plate right side up on your desk.  Disengage the mouse's cord from the
strain-relief slot in the upper half of the shell, then flip the circuit board right side up and put it in place
on the bottom plate (handle the board by the edges).  There are 2 slots at the top of the board and 2 in
the sides that align with plastic support posts on the plate, and the wheels fit into cutouts of their own in
the board.

If you look at the wheel concerned (the one for vertical movement), you'll notice a couple of things. 
First, its edge has square "teeth", like a cog.  Second, there's a little semiconductor device on each side
of the wheel, out towards its edge.  One is transparent and one looks black.  The transparent one is an
infrared-emitting diode, and the dark one is a pair of infrared-detecting diodes (in one pkg).  The IRED
emits a beam of infrared light which the diodes detect.  In the gap between the two are the "teeth" of the
wheel.  As the wheel turns, they alternately block the beam and let it through, which is how the mouse
detects motion.

There seem to be two problems with SmartMouses: the IR signal seems to be "weak" or something and
the board construction seems to introduce a certain amount of stress in the leads of the devices, which
eventually causes them to bend slightly.  When that happens, the photodiode can no longer "see" the IR
beam properly, and it stops registering motion.

So what you need to do is bend them yourself until motion on that axis starts working again.  A pair of
forceps, if you have them, is a handy tool. You could also use needlenose pliers, tweezers, or maybe
your fingers -- in any case, just be gentle.  Start by getting both devices straight and square with each
other, and aligned properly with the wheel slots (not in too far, so that the solid part of the wheel blocks
part of the beam, and not too far out, so that the TEETH don't block the light).  Then just start giving
them little tweaks until you find a position where it starts working (on my mouse, they each actually
point downwards slightly).  It won't take much adjustment, but it will take a little trial and error.  If it
starts working, put the shell together again w/o the screw, pop in the ball, and check it -- it may take a
couple of cycles to get it, but that's all there is to it.

When I first got my mouse, I had to do this several times within the first month or so, but it's worked
without problems for years since (it was in one of the first batches CMD made) -- I guess the stress just
has to be worked out of the leads.

(Ed. again: In my case, it took just a gentle nudge with my finger to move the device very slightly and
everything worked fine again.)

(From The Interface, newsletter of Fresno Commodore User Group, via the Commodore Information
Center, http://home.att.net/~rmestel/commodore.html)