Cleaning a rubber-pad-against-PCB keyboards

[hjalfi]

Hello,

I recently picked up a Canon TypeStar 4 typewriter in a junk shop. The keyboard is really nice, linear and light but tactile, and I am amusing myself by refitting the keyboard as a PC USB keyboard.

The keys are discrete integrated slider-over-spring-over-conductive rubber dome-over-PCB. Each key 'switch' has its own removable assembly containing a dome, clicker, slider etc, all mounted in a metal frame, with the PCB bolted to the back. Pressing a key causes a conductive rubber pad to press onto contacts on the PCB. There's a good teardown here: viewtopic.php?f=62&t=19859&start=

I've done all the electronic modifications, wiring it up to the microcontroller and adjusting the keyboard matrix to add some more modifier keys as the original keyboard only had one (yes, really!), but am now finding that the keys are a little unresponsive. I suspect that while I've been working on it the pads have gotten dirty and are no longer making good contact.

I've cleaned the PCB itself with IPA, but PCBs are pretty robust. The pads I know less about. The wrong solvent could very well cause them to melt and I'll never replace them. What's a good (i.e. non-fatal) way to clean these?

[Howard81]

Press lightly and drag over a piece of standard white paper. A small amount of rubber will stick to the paper. The trick is to just do it enough to remove the shine. Wash and dry, then reassemble!