Some info about contacts: Contacts are generally made out of copper
that is plated usually with brass, nickel or tin.  The plating makes
the contact last longer.

There are basically three things that make contacts fail:

1. Tarnish.  This happens with age.  Too much Tarnish and the contact
no long conducts electricity.

2. Carbon buildup.  As the contacts arc and spark carbon builds up over
time.  Carbon is not a good conductor of electricity.

3. Contact Burn.  After a very long time the plating on the contacts
wears out and the contacts become copper to copper.  Copper, although
a good conductor, is a soft metal and melts at a fairly low temperature.
As the contacts arc and spark the copper gets uneven and develops pits.
As the contacts get more uneven they get unreliable mechanically and
also carbon tends to build up.  Sometimes the contacts will melt and
sometimes even fuse together.  After a while the contacts fails
altogether.

One thing I learned the hard way years ago: Never, never use sandpaper
or emery cloth on a contact.  Doing so removes the plating, leaving
only the copper.  In a very short time the contacts melt and burn and
no longer work.

Years ago I was repairing a mechanical pinball machine with lots of
relay contacts and I used sandpaper.  The machine ran for about week
and then stopped working.  Most of the relay contacts had burned and
were no longer reliable.


Cleaning contacts:

There are two things that clean contacts well.  The absolute best is
an ordinary [rubber] pencil eraser (like you find on the end of a #2
pencil).  I know it sounds overly simple but it works _really_ well.
If you can get the eraser in between the contacts, it cleans tarnish
and carbon buildup better than anything.

Sometimes you can't get a pencil eraser in between a set of contacts,
so the other item to use is a Radio Shack product called Color TV Tuner
Cleaner.  Older TVs with mechanical tuners have mechanical contacts.
The thing that usually fails in these is that the contacts get
tarnished and no longer conduct.  Spraying some Color TV Tuner Cleaner
in the mechanism and running the channel changer back and forth a few
times usually fixes the problem.  Running the channel changer back and
forth causes rubbing action; that, along with the Color TV Tuner
Cleaner, washes the tarnish away.

Reed switch contacts (like you would find under the keys of an organ)
and relay contacts can also be cleaned with this same product.  The
key is to get the rubbing action that the TV tuner has when changing
channels.

What I found what seems to work best for this is a strip of Xerox paper
folded in half over so that it is about 1/4-inch wide.  I liberally
spray the Color TV Tuner Cleaner on the paper and then run the strip of
paper back and forth between a set of contacts held closed.  In fairly
short order all of the tarnish and carbon buildup is cleaned away and
ends up on the paper.  Any excess cleaner evaporates (although I don't
think you want to get this stuff on bare wood as it may stain).

Musically,
Ray Finch