IN THE BEGINNING
Since the first phone that was sold, there have been electrical contacts in
phones. Originally, the only contact was the hookswitch. It didn't take long
to realize that two pieces of metal touching in the same place every time, was
not a switch that was going to last a long time. The spark that occurred when
the switch was operated left some carbon residue. Eventually, the electricity
had a hard time flowing through the built up carbon, and the switch stopped
On low current applications, there is usually no spark, but a coating
develops over the two pieces of metal - kind of like the gook that covers your
windows before you wash them - and the electricity has a hard time passing
through this coating which acts like an insulator.
Later phones began using self cleaning contacts. This works by designing
the two pieces of metal so that instead of touching in the same place each
time, one of the contacts slides over the other a little when operated.
Designers then found that if they put a piece of knife shaped metal on the
contact, facing opposite directions on each side, the scraping action of the
"blades" would get the best cleaning action.
ITT was one of the first companies to change over from metal contacts on
their telephone dials to conductive rubber buttons that short out two traces on a PC
board. This cut down the number of times that the dials would fail - but on
ITT's first dials, they used some pins that would slide into sockets to
connect the dial electronics to the button PC board. They used a cheap
material for the pins and sockets, so oxidation would develop pretty quickly.
The fix was to slide the board with the connector up and down a few times on the
pins, to clean off the oxidation. This would fix it for a little while, but a
new dial was the real fix.
THEY'RE THE SAME - BUT NOT REALLY
The rubber button type keys are not self cleaning, but because of the size
of the area that makes contact, there are relatively few contact problems
except in really dirty environments where the traces or buttons can get
covered with non-conductive stuff.
Most telephones use conductive pads that are conductive thru and thru. If
these buttons stop working right you can usually clean them with a pink type
pencil eraser (very mildly abrasive) on the rubber pads, and on the traces on
the circuit board. Be careful with the traces on the circuit board that are
not shiny metal, but a raised carbon track. It's easy to take off too much of
the conductive material, and the trace will be dead. If you do kill it, use
a conductive paint made for PC boards to repair it - DON'T use our rubber
button repair paint on the circuit board! You can also get a conductive pen that you
can just paint over the metal or carbon trace, but that may not stick to the
trace that's constantly being hit by the button?
It's easy to test the conductivity of a rubber pad or PC board trace.
Simply use your ohm meter across the face of the rubber pad (not on the
sides). On most pads, you will see 100 to 200 ohms. If you test a bad pad, it
will often read 500 to 10,000 ohms or more. After using our rubber button
repair paint, you will see less than 10 ohms. Metal traces will usually be a
direct short, but carbon traces could be less conductive. Comparing working
buttons to non-working buttons will usually be your best guide. In general,
you shouldn't use any chemicals on the rubber buttons or the traces to clean
them...use only a pink pencil eraser.
There are some phone systems that use conductive pads that are
conductive thru and thru. On these phones, EVERY phone will end up coming back
for a button problem!
In the early eighty's, Japan was producing lots of toys with lots of
buttons. A Japanese company designed an ink that would coat non-conductive
pads on these toys, making these toys pretty inexpensive to produce. This ink
dries out eventually, and flakes off the pad. You can often see these little
black flakes transferred to the PC board. When the toy stopped working...you
just tossed it in the garbage. The aforementioned companies are using this
same ink in their business phones. They would be quite happy if you tossed
their phone when it stopped working, but they are almost as happy to have you
send them the phone for repair, for $50 to $80 or more. This is no accident.
These companies consider this an annuity. They sell you the phone knowing
that you have to send it back for repair a couple of times through its life,
or throw it away and buy a new one.
Other companies do the exact same thing, but with a different part. The
hookswitch is another popular annuity for phone manufacturers.
If you go in and try to clean a pad with an ink coating, you just remove
more of the coating...and usually the button won't work at all. If you use a
chemical to clean these buttons - they're dead for sure. Different repair
companies have been using different stuff to repair these pads to make them
conductive. I've seen alarm foil super glued to the pads, graphite coatings
and all kinds of carbon, silver and gold conductive paints. It all flakes off
the button after a while, until now!
In October of 1992, I asked a chemical company if they could come up with a
solution to this problem. They seemed to think that it would be a pretty easy
fix, and they sent me a few prototypes. After some testing, they realized that
they all flaked off the pad after a while, mainly because they would dry in a
non-flexible state. They continued to work on the problem for many months.
They finally sent me a prototype that would definitely work - they had tested
the heck out of it and it wouldn't fall off the button. This prototype was
adhesive backed copper foil "dots". The adhesive was the secret,
which was specially formulated to adhere to the rubber pad, and would never
dry out. I sent some of these prototypes out to some customers, and everybody
felt that it was much too time consuming to stick these "dots" on
every button in the phone. The phones that used the ink needed EVERY button
done, because the ink would flake off of all the pads eventually (and cause
lots of comebacks).
The chemical company went back to the drawing board armed
with knowledge of what chemicals were needed to adhere to the buttons. In June
of 1993, they came up with a two part mixture that turned into silicone rubber when it
cured, and it stuck to the button so well that they needed a razor blade to
cut it off the button...it couldn't be pulled off. The two part mixture was
90% silver colored goo, and 10% clear liquid that got mixed together. There
was a 20 minute working time, which meant you had to work fast to paint as
many buttons as you could in 20 minutes.
They spent months trying to change the formula so they could put
it in two syringes, allowing you to lay down two equal strips of stuff, so it
could be mixed up as needed. This stuff is like an epoxy...once it's mixed it
starts to cure, and there's no way to stop it. There was no way that anyone
could mix only a portion of the 90-10% mixture in the field since you were
dealing with small quantities and a lopsided mixture that had one component
that was only 10% of the mixture. You'd need laboratory equipment to cut it in
half, and if you messed it up the stuff wouldn't adhere to the button,
wouldn't be conductive, or it wouldn't have good durability.
Speaking of durability, they tested this stuff on a custom made machine
that pushed the button on an actual NEC or Comdial button assembly, counted
the mechanical keystrokes, and counted the electrical impulses on the PC
board. They have tested this stuff over to over 500,000 operations, and the
two counts were the same, it didn't flake off the button, it stayed just as
conductive as when it was put on, and was so durable that you couldn't even
see the pattern of the PC board traces on the pad after 500,000 pushes!
In October of 1993, they decided that they couldn't make it anything other
than the 90-10% mixture, it just would lose one of the properties it needed.
They started production of the Rubber Button Repair Kit, and it has worked
great! Using the whole bottle at one time may not be perfect in terms of
economy, but even if you only fix one phone, it's still a lot cheaper than
sending the phone out for repair and waiting for it to come back. Many guys
are taking the rubber buttons out of junk phones, and painting them in advance
all at one sitting. They use these to do repairs, and save the old ones into a
box, so they can repair them when they have a chance.
Since then they've tuned the formula to give you maybe
a day or two of working time if you keep the bottle with the mixed
epoxy closed when you're not using it.
We've learned a couple of things along the way from our customers:
First, you must clean the button with Acetone (pure Acetone, with no oils
or coloring) before applying our stuff. If you leave the old ink on the
button, or a previous repair if it's not a virgin phone, our stuff will stick
to the ink or the old repair - which will then flake off the button. Don't
bother to use this stuff if you don't want to clean the buttons first!
you must wipe off any repair material you get on the flat part of the rubber
mat that sits on the PC board. If you don't wipe it off, it may short out the
traces that are running all over the PC board, and none of the buttons will
work. You can use a little Acetone on a swab to clean it off if it has started
to cure, or a knife edge to scrape it off if it's still wet. When painting, a
thickness of 3 mils (about 3 pieces of scotch tape thick) works best.
you must mix the clear liquid in the brown bottle (Part B) into the silver goo
(Part A) as soon as you open it. It readily picks up moisture
from the air, which stops the mixture from working right. The chemical company
changed their formula in January of 1994, to help prevent these problems if
you do leave it open, but why ask for trouble? The Part B bottle is now also
sealed with Nitrogen. You can leave it open for a maximum of fifteen minutes
before you will screw up the formula! A good indication that the chemical
reaction didn't occur properly is that it will never harden, or the silver
particles will rub off on your finger after it does harden. The epoxy has a 2
day working time, it will stay workable for a while so you won't have to rush
before the stuff gets hard. The shelf life of this product should be at least 6
months from the date of manufacture if left unopened.
don't try to make the chemical company's formula better. These guys are pros.
They talk about molecules and stuff like that (I never did well in chemistry
in school), and they have the proper knowledge and equipment to design and
test this stuff. Adding your own stuff to the mixture will definitely make one
of the needed properties worse!
Get a small bottle cap or something to put the
Pure Acetone in to dip the cotton swap in, to
clean the buttons. You should see black stuff coming off the buttons onto the
swab as you clean them. Acetone is a great solvent and dries quickly. Dip the
brush in Acetone every couple of minutes and wipe the brush onto a paper towel
to make painting easier.
On Comdial phones and some other business systems as well as many cordless
and consumer phones, they've used melted over plastic posts to hold the
circuit board together instead of screws. Some guys have told me that they
use epoxy, hot glue or try to re-mush over the plastic posts to get them back
together. About 20% of the Comdial phones that come in for repair have plastic
posts broken off along the bottom anyway because the people have been
pounding on the buttons to get them to work. They are used to pounding on
these buttons, and will continue to pound on them after you fix them
correctly. The shock of the pounding will cause the above repair methods to
fail. The only dependable repair I have found is to cut the mushed over
plastic off the post flush, with a flush cutter or razor blade to get the
keyboard open. To close it, drill a hole in the middle of each post, and use
a tiny screw and washer (use a plastic washer if there are traces next to
the post) to hold the board down.
The most popular phone system made today with
ink-coated buttons is the Avaya IP Office. Our Rubber Button Repair Kit
will repair the intermittent button operation.