Keyboards & Conductive Rubber

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