David, thanks for that.  To recap then, you're saying that even though there
may be no visible dirt or gunk anywhere in the 'ball pit', it's possible
that the light-admitting slits may be partly obscured?  I take it these
slits are not immediately visible when the ball is removed?

Ian Porter
Computer Guys
Arrowtown
New Zealand
[log in to unmask]

----- Original Message -----
From: "David Gillett" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, April 24, 2002 5:46 PM
Subject: Re: [PCBUILD] Derailed mice


> On 23 Apr 2002, at 21:19, Ian wrote:
>
> > Anyone know why mice go bad?
>
> > I don't mean dirt in the mechanism, I mean the jerky, patchy
> > behaviours that some mice begin to exhibit after varying periods of
> > time.
>
> > Sure, I know that a busy CPU can affect them too, but I've seen
> > this flakiness occur when nothing has been running, background or
> > otherwise. Like yesterday.  Went to fix an email problem for a
> > customer and she had a crazy mouse. Looked inside - no dirt.
> > Checked the connection - no probs. But the mouse still wouldn't
> > behave.
>
> > Sold her a new mouse - voila!  No problems - customer over the
> > moon.  Thinks I'm brilliant.
>
> > Well....I can't be.  Cos I can't tell her why the first one
> > crapped out.
> >
> > Ian Porter
> > Computer Guys
> > Arrowtown
> > New Zealand
> > [log in to unmask]
>
>
>   Well, there ARE two places where dirt in the works could induce
> "patchy behaviour" in a typical mouse:
>
> 1.  The most common scenario I've seen is a build-up of "gunk" on the
> rollers, around the point where the ball touches them.  This can lead
> to a loss of friction between the mouse and the rollers -- the mouse
> moves, the ball rolls, and the rollers don't.
>
> 2.  Each roller is attached to a wheel with slits in it, which passes
> between a tiny light source and a photoreceptor.  If dirt blocks the
> slits, the ball rolls, the roller turns, and the photoreceptor
> doesn't notice.
>
>
>   The ball is pressed slightly against the two sensor rollers by a
> sprung third roller, set at a 45-degree angle.  I HAVE seen one mouse
> where the spring for this third roller was not up to snuff, with the
> result that when the mouse was moved suddenly in certain directions,
> it could lose contact with one or both of the sensor rollers.  That
> would be a non-dirt loss of friction, and might be another cause for
> the problem you've described.
>
>   (I've also had one cheap mouse where the microswitch under the
> primary mouse button eventually wore out, but that didn't affect
> movement of the cursor, so I'm pretty sure that's a different
> problem.)
>
> David Gillett

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