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'[OT] conductive coating for rubber membrane keypad'
1999\11\25@042047 by Lee Jones

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Hi all,

I'm looking for a small quantity of conductive coating to
repair a rubber membrane keypad.  I got some oil between
the rubber membrane and the PC board.  Alcohol cleaned off
the oil just fine.  But my overly vigorous scrubbing with
a Q-tip also removed the conductive coating on a few keys.

This is the style of keypad where there are interlaced
fingers on the printed circuit board.  Underside of each
key is a dome of rubber with a raised spot in the center.
The raised spot is coated with a conductive substance.
When the key is pressed, the conductive coating closes
the circuit by "shorting" the fingers together.

Anybody know if this conductive coating is available for
repair work?  If so, a vendor and part number would be
nice.  Or is this material the exclusive province of the
people who make rubber membrane keypads?

Thanks in advance.
                                               Lee Jones

1999\11\25@052635 by Andrej Nemec

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Try to contact the manufacturer of the product containing this rubber
keypad for a new keypad. With some luck you will get it for almost nothing.

Some times ago I've tried to repair a keypad on an older Fax machine.
The amount of work (time) for this task exceeded the cost of a new one
(Fax).
Of course if somebody would pay me for the time I spent on this.

There are a few methods for repairing.

- thin self adhesive copper foil could do it.
- carbon paint for silkscreen printing could do it.
- gold foil for repairing letters on thumbstones could do it.
- a conductive silver spray could do it.

Any other sugestions ?

Regards, Andrej

----------
{Quote hidden}

1999\11\25@054754 by paulb

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Lee Jones wrote:

> Anybody know if this conductive coating is available for
> repair work?

 Colloidal graphite paint was traditionally called (probably a
trademark) "Aquadag", as used on the outside of CRTs.  Presumably
similar, two potential problems: Will it stick?  Where do you get it?

 Same problem with any product I fear.  The repair material for rear
window demisters is *ridiculously* expensive, so I never repaired my
electronic typewriter keyboard.
--
 Cheers,
       Paul B.

1999\11\25@072011 by Morgan Olsson

picon face
Hej Lee Jones. Tack fšr ditt meddelande 10:20 991125  enligt nedan:
>Hi all,
>
>I'm looking for a small quantity of conductive coating to
>repair a rubber membrane keypad.

Problems:
1) to get it stick on the key
2) to not rub some off between the fingers of the PCB...


Probably easiest is to get a old TV remote or such, and rip off the keyboard.
Then nip off the condictive pads using a very good end nipper.
Do the same on the keyboard you repair.
Tne glue the good pads in place using a good rubber glue.
There is one called Alusol (i think) that is for repairing boots.
Very durable, though, and a bit flexible.

Another idea is to get the metal disc from a keuborad that use the technology of a bent disc that "clicks" down at the PCB when pushed.

As this all takes time, I once did a "repair" by adding a row of normal panel mount pushbuttons outside the original keyboard.


/Morgan

1999\11\25@083355 by wwl

picon face
On Thu, 25 Nov 1999 11:24:27 +0100, you wrote:

Chemtronics do a kit specifically for repairing rubber membrane
keypads - targeted at the remote-control market. Quite expensive I
think - maybe your local TV repair shop has some.
{Quote hidden}

1999\11\25@101058 by Wagner Lipnharski

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You can start with school white glue and graphite powder (from pencil),
mix it and apply a small disk directly to the rubber. It will hold for
some months. The graphite quantity into the mix will define the contact
resistance.

For final results, try another strong glues as Araldite or some
epoxies.  Copper powder, as well silver, bronze or brass powder into the
glue mix does marvelous results.  The ideal is that the "pill" should be
a little flexible to make good contact at the pcb fingers every time.
Remember that some glues as Silicon "wraps" the powder particles in the
mix, electrically isolating them

Grab a big truck and goes after "not working" nintendo or sega
controllers, you will find them in large quantities around, probably you
may have a couple at home. They are quite strong and the "pills" are
doped to stand kids abusing it. Just remove and "work" those pills
before glue it to your rubber keypad.

1999\11\25@110540 by V sml

picon face
Has someone suggested a conductive pen?  It contains silver ink.
Cost about US$15.00 here.  I can't remember the brand.  Give me a buzz
if you want to use this solution, and I will try to schedule a trip
down to the electronics shop to check it up.

Ling SM

>> I'm looking for a small quantity of conductive coating to
>> repair a rubber membrane keypad.  I got some oil between
>> the rubber membrane and the PC board.  Alcohol cleaned off
>> the oil just fine.  But my overly vigorous scrubbing with
>> a Q-tip also removed the conductive coating on a few keys.

1999\11\25@120048 by Keelan Lightfoot

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face
Have a look at:

http://www.sandman.com/rubberb.html

There is also some good information on how to repair these buttons at that
page.

- Keelan Lightfoot

> I'm looking for a small quantity of conductive coating to
> repair a rubber membrane keypad.  I got some oil between
> the rubber membrane and the PC board.  Alcohol cleaned off
> the oil just fine.  But my overly vigorous scrubbing with
> a Q-tip also removed the conductive coating on a few keys.

1999\11\25@130817 by Dwayne Reid

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face
>Hi all,
>
>I'm looking for a small quantity of conductive coating to
>repair a rubber membrane keypad.  I got some oil between
>the rubber membrane and the PC board.  Alcohol cleaned off
>the oil just fine.  But my overly vigorous scrubbing with
>a Q-tip also removed the conductive coating on a few keys.

Circuit Specialists (Active, FAI, Arrow, Digikey) make a product for this
very purpose.  A tad expensive, but will do a LARGE number of repairs IF you
do them all at once.  Its a 2 part product - once you add the accelerator,
you have a limited working time.  Does work well, though.

dwayne


Dwayne Reid   <EraseMEdwaynerspam_OUTspamTakeThisOuTplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

Celebrating 15 years of Engineering Innovation (1984 - 1999)

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
Do NOT send unsolicited commercial email to this email address.
My posting messages to Usenet neither grants consent to receive
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email.

1999\11\25@140843 by Russell McMahon

picon face
You could consider trying the conductive silver paint sold for PCB track
repair.
There is a certain art in using this.

It is generally NOT conductive when whet and relies on the nonconducting
binder evaporating away and leaving the silver in contact. Once you have the
knack it makes OK PCB tracks.

May be incompatible with your rubber though ???




     Russell McMahon
_____________________________

>From other worlds - http://www.easttimor.com
                               http://www.sudan.com

What can one man* do?
Help the hungry at no cost to yourself!
at  http://www.thehungersite.com/

(* - or woman, child or internet enabled intelligent entity :-))

From: Lee Jones <leespamspam_OUTFRUMBLE.CLAREMONT.EDU>
{Quote hidden}

1999\11\25@142123 by l.allen

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    Russell McMahon wrote....

> You could consider trying the conductive silver paint sold for PCB track
> repair.
> There is a certain art in using this.
>
> It is generally NOT conductive when whet and relies on the nonconducting
> binder evaporating away and leaving the silver in contact. Once you have the
> knack it makes OK PCB tracks.
>
> May be incompatible with your rubber though ???
>

We use spray on nickel coating...
I spray a bit onto a card, then use a small paint brush to apply it
directly to the pad.

The trick is to leave the nickel to dry for 8 hours to reach min
resistivity, but will work in a membrane application within half an
hour since the scan is tolerant of a high-ish resistance.


_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

1999\11\25@172006 by Des Bromilow

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face
Couple of suggestions.

#1, get a thin layer of contact cement on the substrate and then dust it with powdered graphite. This should give you a conductive pad.
#2, get a cheap calculator (cost less than $10) from the import store, and shave a sliver or two off the pads under it's keys. The glue them onto you pads (correct side up of course) I know if several kids toys that may be a cheaper source of pads than calculators... eg: those tacky little mobile phone filled with lollies that play music.

Both of these suggestions are only that, so don't sue me if there's flaws in my reasoning.

Hope this helps,
Des

>>> Lee Jones <@spam@leeKILLspamspamFRUMBLE.CLAREMONT.EDU> 11/25/99 7:20:48 pm >>>
Hi all,

I'm looking for a small quantity of conductive coating to
repair a rubber membrane keypad.  I got some oil between
the rubber membrane and the PC board.  Alcohol cleaned off
the oil just fine.  But my overly vigorous scrubbing with
a Q-tip also removed the conductive coating on a few keys.

This is the style of keypad where there are interlaced
fingers on the printed circuit board.  Underside of each
key is a dome of rubber with a raised spot in the center.
The raised spot is coated with a conductive substance.
When the key is pressed, the conductive coating closes
the circuit by "shorting" the fingers together.

Anybody know if this conductive coating is available for
repair work?  If so, a vendor and part number would be
nice.  Or is this material the exclusive province of the
people who make rubber membrane keypads?

Thanks in advance.
                                               Lee Jones

1999\11\25@194108 by Brian Kraut

picon face
I believe that the coating is carbon powder.  I have no idea how they
get it on..  You could probably pull the carbon rod out of a dry cell
and powder it with sandpaper.  Put some kind of adhesive on the rubber
and dust the powder on.  There are also some conductive epoxies and the
CircuitWorks conductive ink pen.

One thing I know will work for sure is the thin adhesive backed copper
foil that is sold for wiring in dollhouses.

Lee Jones wrote:

{Quote hidden}

1999\11\25@194523 by Brian Kraut

picon face
I have found that the conductive ink pens really suck for circuit board repair,
but they work great for cracked traces on the thin ribbon conductors that are
used on membrane keyboads.

Russell McMahon wrote:

{Quote hidden}

1999\11\26@054433 by William Kitchen

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> Probably easiest is to get a old TV remote or such, and rip off the keyboard.
> Then nip off the condictive pads using a very good end nipper.
> Do the same on the keyboard you repair.
> Tne glue the good pads in place using a good rubber glue.
> There is one called Alusol (i think) that is for repairing boots.
> Very durable, though, and a bit flexible.

Ordinary super glue sticks very well to rubber and most rubber-like substances.
The only catch is that the resulting layer of glue doesn't stretch with the
rubbery material. But for areas that are very small or don't have to
stretch much, it's hard to beat.  I doubt that the contact pads of a rubber
keypad will be any problem at all.

--
                                       Peace,
                                       William Kitchen
The future is ours to create.

1999\11\26@173503 by Leo

picon face
Hi friends,

referring to the origin of the tread, the msg of Lee Jones, I have been the
same problem of miss contact on the cordless phone (Daewoo) and on the IR
television remote control (Philips).
After opening teh two keypad, I have found between the rubber and the PBC
some liguid that seems oil, but believe me, no member of the my family put
oil on telephone or remote control.
After cleaning with more accuracy and delicacy the PCB and the black rubber
spot all the two keyboard return to work correctly.

But I'm curious to know th origin of the oil. I think a possible sweat of
the rubber ??

Ciao

Leo

1999\11\26@173924 by David Duley

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On Thu, 25 Nov 1999 12:42:22 +0100, you wrote:

{Quote hidden}

Ive done this with aluminum foil glued with spray adhesive to the
underside of the membrane.

Dave Duley

1999\11\26@184906 by Wagner Lipnharski

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Leo wrote:
>
> Hi friends,
>
> referring to the origin of the tread, the msg of Lee Jones, I have been the
> same problem of miss contact on the cordless phone (Daewoo) and on the IR
> television remote control (Philips).
> After opening teh two keypad, I have found between the rubber and the PBC
> some liguid that seems oil, but believe me, no member of the my family put
> oil on telephone or remote control.
> After cleaning with more accuracy and delicacy the PCB and the black rubber
> spot all the two keyboard return to work correctly.
>
> But I'm curious to know th origin of the oil. I think a possible sweat of
> the rubber ??

Hi Leo, working to IBM as mainframe engineer sometimes we use to fix
some computer terminal keyboards (at that time we needed to open
keyboards and fix them <g>), and you will not believe about things we
found in the middle (and below) the keys...  First that those things you
would never suppose to see inside a computer room...and second that some
of them were impossible to be there, as for example one of those lady's
fake nails... red...stuck below the Enter key, BUT there was no female
operator at that room... !?!? hmmm.

The normal skin oil and humidity (perspiration) is enough to enter and
accomodate below the contacts.

Perhaps it was a special oil from the factory... do you already saw
special grease proposital applied at automobile electrical connectors?

1999\11\27@015051 by paulb

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Brian Kraut wrote:

> One thing I know will work for sure is the thin adhesive backed copper
> foil that is sold for wiring in dollhouses.

 Can you run that one past us again?
--
 Cheers,
       Paul B.

1999\11\27@032419 by William Chops Westfield

face picon face
   > One thing I know will work for sure is the thin adhesive backed copper
   > foil that is sold for wiring in dollhouses.

     Can you run that one past us again?

Ahh.  Non-traditional sources of materials!

If you go into a better "arts & crafts" stores, you will find adhesive
backed copper foil.  It has a couple of uses:

1) Flat dollhouse wiring.  You run this along the walls and ceilings of
  more elaborate dollhouses, to provide electricity for the overhead
  lights and such.  (even elaborate doll houses lack engineering nicities
  like hollow walls and ceilings!)  You can paint or wallpaper over it and
  it won't show as much a normal copper wire of equivilent current
  handling capability.

2) Edging for "stained glass" work.  After you have your cut glass pieces,
  you put copper tape over the edges, and then run soldor over the copper
  to create the "framing" for the finished stained glass piece.

Neither of these is designed for electronics repair - they probably won't
result in a conducting link to existing traces just by applying the tape,
for instance.  I'll bet you can find some "samples" of assorted conductive
tapes designed for RF shielding and such that IS made with explicitly
conductive adhesive...

BillW

1999\11\27@042552 by Jinx

face picon face
> Brian Kraut wrote:
>
> > One thing I know will work for sure is the thin adhesive backed copper
> > foil that is sold for wiring in dollhouses.
>

A problem you may encounter at some time in the future is that of
the copper tarnishing. It'll work well for a while but, unless there's some
friction/self-cleaning action of the other contact, eventually the copper
will need scrubbling.

BTW, you mightn't be able to make use of it in this app, but a friendly
jeweller or PCB mftr they may throw any small copper items that
need a permanent conducting surface into the basket to give it a
free thin gold plating. It's of miniscule cost and effort to them. I use one
from time to time, who doesn't mind as long as I don't ask too much.

Jinx

1999\11\28@184219 by Leo

picon face
> Hi Leo, working to IBM as mainframe engineer sometimes we use to fix
> some computer terminal keyboards (at that time we needed to open
> keyboards and fix them <g>),

You are referencing to the 3277/78 and 3741/42 capacitive keyboard???

Do you remembre the first E.C. that ship a semitrasparent membrane to
install betweem the keyboard plate assembly (black) and the key??

he he he ... also I was an IBM man on 370/115, 125, 135, 138, 148, 4331 and
4341and all related I/O. Was a great time...


Ciao

Leo

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