Bad Volume Control on a //c

[Aaron Heiss <heiss@deletethis.pdx.edu>]

I have an Apple //c (my main computer now, actually) that was given to me
seven years ago by someone who found it in an attic, where it probably sat
for a good few years prior.  Its volume knob has never worked properly for
me.  If it is set to anything over about two-thirds maximum, the speaker
works flawlessly (and it's *loud*!); if it's set in the bottom third of
its range, no sound is produced at all.  In between it sometimes works and
sometimes doesn't, but usually can be persuaded to make noise if the knob
is physically wiggled by pushing it.

I assume the machine's history that this problem is due to dust in the
potentiometer.  I have taken the machine apart and cleaned it thoroughly
(something I do with all new computer acquisitions)  to no avail; I have
tried spraying "canned air" at it when it was apart, and have noticed no
result from that either.  The only thing that I have not done yet is to
remove the motherboard from the bottom case half, which might help with
access with the canned air, but which does not look trivial.

Has anybody else any experience with this sort of problem?  Is there some
trick to getting dust out of awkwardly placed potentiometers?  Is it
possible that this is not a dust problem in the first place?  I'd rather
not have to take out and resolder the knob to clean it properly or to
replace it (though I could if I had to), so I'm asking here first.  I'd
appreciate any tips that could be passed my way.

Thanks in advance!


Aaron Heiss

heiss(AT)pdx(DOT)edu
http://web.pdx.edu/~heiss/