6 Sep
2004
6 Sep
'04
10:10 p.m.
Hi Guys,
I'm trying to revive a keyboard (integrated into a vintage computer so
it's kinda important) - this is the kind where there's a PCB with lots of
"pads" in the scanning matrix, and the keys push a little pad of
"conductive
rubber" down onto the PCB pads to make the connection.
Several of the keys on this keyboard require excessive pressure to make
contact - I've tried cleaning the pads, and (gently) the surface of the
rubber, however it appears that the rubber has increased in resistance.
The good keys measure 200-300 ohms from one end of the conductive rubber
pad to the other with only mild pressure - the bad keys measure 5k-10k
unless you really squeeze them - under pressure they drop to 1k - 2k,
which appears to be barely enough to trigger a detection.
Anyone know what the failure mode is? I though perhaps the rubber bits
had cracked, however this does not appear to be the case.
Anyone have any tips/tricks to fix this problem?
Regards,
Dave
--
dave04a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Vintage computing equipment collector.
http://www.parse.com/~ddunfield/museum/index.html
6 Sep
6 Sep
6:24 p.m.
Hi Guys,
I'm trying to revive a keyboard (integrated into a vintage computer so
it's kinda important) - this is the kind where there's a PCB with lots of
"pads" in the scanning matrix, and the keys push a little pad of
"conductive
rubber" down onto the PCB pads to make the connection.
This design is still common in remotes. That where you will get new
pads from. Cutting off old and gluing good conductive pads on is
matter of excerise up to yours.
Oh, the failure mode losing conducivitiy in pads themselves like
this is really common too. This what we had to replace remotes or
repair them with good pads from another in our TV shop. We have
about six legal size filing boxes full of those remotes.
Cheers,
Wizard
11:50 p.m.
Hi Guys,
I'm trying to revive a keyboard (integrated into a vintage computer so
it's kinda important) - this is the kind where there's a PCB with lots of
"pads" in the scanning matrix, and the keys push a little pad of
"conductive
rubber" down onto the PCB pads to make the connection.
[...]
The good keys measure 200-300 ohms from one end of the
conductive rubber
pad to the other with only mild pressure - the bad keys measure 5k-10k
unless you really squeeze them - under pressure they drop to 1k - 2k,
which appears to be barely enough to trigger a detection.
I've seen this happen. My TRS80 M4 keyboard (which uses individual
keyswitches which use this technology) had this sort of problem. Of
course there I could move them around to put the bad ones on the least
used keys (like the numeric keypad).
Anyone know what the failure mode is? I though perhaps the rubber bits
had cracked, however this does not appear to be the case.
Anyone have any tips/tricks to fix this problem?
Two ideas :
1) Rub a _soft_ pencil (I manged to get a 6B) over the rubber pads. This
will put a new graphite layer down.
2) Chemtronics sell (sold?) a repair kit for these pads. You mix the 2
parts and then put a drop on each of the pads. The problem is that once
you've misxed the 2 parts you have to use the kit in a day or so, and
there's enough stuff for quite a few switches -- and it's not cheap. It's
therefore probably not worth doing for one TV remote or something, but it
might be just right for a keyboard.
-tony
7 Sep
7 Sep
12:42 a.m.
1) Rub a _soft_ pencil (I manged to get a 6B) over the
rubber pads.
"Managed to"? Any art-supply store should have pencils in a wide
variety of hardnesses, including the very soft.
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2:16 a.m.
Dave Dunfield wrote:
Several of the keys on this keyboard require excessive
pressure to make
contact - I've tried cleaning the pads, and (gently) the surface of the
rubber, however it appears that the rubber has increased in resistance.
The pads either wear or "dry out" or something, never worked out which.
I talked a mate of mine through repairing some vintage synthesizers
which use conductive pads for the control panel (Sequential Six-Trak,
Alesis drum machine and sequencer) by taking the panel apart and
painting a blob of silver-loaded paint for repairing heated rear windows
in cars. The bottle was a couple of pounds from Halfords, and probably
cheaper in your local independant motor factors. A tiny bottle lasts
for ages because you only need a little spot.
Gordon.
6:04 a.m.
Dave;
I've tried several things on my Sony TV remote control. The various
paints and other expensive fixes don't last very long. What finally worked
for me was some heavy aluminum foil tape used for sealing air ducts.
Cut some tiny squares of the tape just big enough to cover the two
contact pads on the circuit board and stick it to the surface of the key
plunger. Evidently the resistance value is not critical, as long as it's
below some minimum value -- zero ohms is OK. My repair has been working for
a couple of years now.
You can find the tape at home centers (Lowe's/Home Depot), and appliance
or plumbing parts suppliers.
Paul Pennington
Augusta, Georgia
5 p.m.
On Tue, Sep 07, 2004 at 07:04:57AM -0400, Paul A. Pennington wrote:
Dave;
I've tried several things on my Sony TV remote control. The various
paints and other expensive fixes don't last very long. What finally worked
for me was some heavy aluminum foil tape used for sealing air ducts.
Cut some tiny squares of the tape just big enough to cover the two
contact pads on the circuit board and stick it to the surface of the key
plunger. Evidently the resistance value is not critical, as long as it's
below some minimum value -- zero ohms is OK. My repair has been working
for a couple of years now.
Isn't the reason the original equipment came with rubber pads was to minimize
wear of the PCB contacts? When I was a kid, the only computer at home was a
Commodore PET (2001-N - 32K, 40 col., AKA 3032 in Europe) One of the most
loaded programs, by me and my 3 brothers, was the machine-language version
of Space Invaders. You move with the 4 and 6 number-pad keys, and fire with
A. Between all of us, we wore the gold off those three pads. I can only
imagine that copper or alumimum foil tape would do it much faster.
My solution to the damaged PCB was to A) buy a new keyboard back (at $35 from
the local dealer), B) salvage the old harness, C) build a frame from an old
Radio-Shack 150-in-1 electronic kit, D) install 3 genuine arcade buttons (about
$8 each at the time), and E) mount them in front of the computer. I wish I
had a picture of it, but it was perfect - with the second keyboard harness, I
was able to mount the buttons in parallel with the keyboard, letting us play
Space Invaders without damaging the new keyboard.
-ethan
--
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8:40 p.m.
Ethan said:
Isn't the reason the original equipment came with
rubber pads was to
minimize
wear of the PCB contacts?
As I said, this has been working fine for a couple of years now. The
channel up and down keys get a LOT of use too.
I'd be afraid copper tape would oxidize and you'd be right back where
you started.
Paul Pennington
Augusta, Georgia
7421
days inactive
7422
days old
7 comments
7 participants
participants (7)
-
ard＠p850ug1.demon.co.uk -
dave04a＠dunfield.com -
dickset＠amanda.spole.gov -
gordon＠gjcp.net -
jpero＠sympatico.ca -
mouse＠Rodents.Montreal.QC.CA -
paulpenn＠knology.net