Just a couple of thoughts on keyboard switch contacts, with no advice
at all about cleaning them -- the others are far more expert than I am.

The plating on switch contacts is indeed critical.  The best of these,
sigh, are silver and gold.

Gold doesn't oxidize under electric arc conditions, so it retains its
electrical properties splendidly, probably forever if there's plenty of
it there; it will deplete through vaporization with use.  Silver does
oxidize, but its oxides are fairly conductive, so the oxidation doesn't
make much difference in a low-current application.

For many years most switch contacts have been made of phosphor-bronze,
which is a reliably springy alloy.  But its oxides have low
conductivity, hence the plating.  Ultimately, the best deal has turned
out to be a phosphor-bronze contact plated with a good thickness of
silver and then overlaid with a very thin flash coating of gold.  This
provides the maximum life for a minimal cost.

There have been repeated attempts to get around the precious metals.
Most of these involve carbon, which is not such a great conductor but
which won't wear out under arc conditions because oxidized carbon is
carbon dioxide, which is a gas, so it doesn't stay on the contact to
contaminate things.  One of the more recent tricks has been to use
contacts of foam plastic that is heavily doped with carbon.  This works
fine until the plastic foam itself breaks down with age.  There is also
carbon-doped rubber, which works better if you can figure out a cement
that'll hold it onto a metal tab for forty years or so.

My guess, and this won't help restorers of antique instruments, is that
modern contacts are infinitely better than anything that went into an
old electric/electronic musical instrument.  I think we've learned more
about contacts in fifteen years of building reliable computer keyboards
than we learned over the last 100 in all other musical instrument
applications.

Well, there _is_ a little advice I can offer about spray-can contact
cleaners.  There are several varieties.  One sort smells a lot like the
now-forbidden carbon tetrachloride and does not leave any residue
behind.

Another uses a fairly strong solvent in which a light oil -- either
petroleum or silicone -- is dissolved.  These will clean the contacts
and leave a bit of a protective shield behind.  For sliding contacts,
this is of considerable benefit, and I used Channel Master Silicone
Shield for many years on audio equipment; both potentiometers and
switches.

And there was, and maybe still is, a rather strange sort of spray
contact cleaner that contained a mild abrasive.  This stuff was good
for TV tuners that were exposed to lots of tobacco smoke: it cleaned,
polished, and left a protective film of oil on the contacts.

I suppose I'd advise trying one of the no-residue cleaners first, and
see how long it lasts.  I'd be careful of the lubricating cleaners:
you don't want the spray to get onto surfaces that may have to be glued
sometime.  There aren't many viable electronic-supply dealers left;
almost everything is Internet or catalog sales.  MCM Electronics (use
Google) is one starting place to look for cleaners.  They've gotten
expensive what with restrictions on the use of Freon.

Mark Kinsler
Lancaster, Ohio USA
http://home.earthlink.net/~mkinsler1