On Sat, 19 Nov 2005 16:10:02 +0000, Rich Webb wrote:

On Sat, 19 Nov 2005 00:00:08 -0700, Hamad bin Turki Salami
wrote:

I have an E-mu electronic music keyboard that was damaged when someone
spilled a drink on it. Four of the keys stopped working after the mishap.

The keyboard works, I believe, by the same principle as a capacitative
computer keyboard. When you press on a key, a black circular part
plunges against a circuit board which has at the point of contact a
corresponding pair of interlocking metal plates (embedded in the board).
I believe the interlocking metal plates are acting as a capacitor, and
the black circle is some kind of insulator that gets between the
plates and changes the capacitance.
[snip...snip...]

I think that you'll find that it's even simpler than that. The pair of
metal plates are simply connected to a "row" and a "column" in the
keyboard matrix and the contact is made by a conductive patch on the
base of the key plunger.

Cleaning the spilled drink probably removed the conductive coating. Try
painting the contact patch area with a conductive paint. Radio Shack has
p/n 640-4339 that would probably work, as would the conductive paint
from a "rear window defogger repair kit."

I do not see how this can be the case. I am unable to make a note sound
by running a wire between the two plates. I am therefore skeptical that
the keyboard works by a simple contact principle. Also, the surfaces of
the metal plates (all of them, not just the damaged ones) are black and
don't conduct well.

Also, it does not seem that the problem is with the black circle that
plunges down. If I shift the rubber strip that the black circles are
attached to, I can realign the black circles with different keys.
When I do that, the problem doesn't shift. The same keys malfunction
and the same keys work, so the problem can't be with the black circles.

Isn't the principle behind common computer keyboards capacitative switches
like I'm describing? My impression is that this kind of switch is much
more reliable than a simple contact kind of switch and would certainly be
favored in a high quality device that is subjected to relentless use,
like a musical keyboard.