If you own an early Roland synth that has aftertouch you have probably experienced that the aftertouch function is not working as is should. You have to press very hard, and the response is not even over the whole keyboard length. This is caused by oxidation of the aftertouch sensor. This diagram shows a cut through the sensor. When pressure is applied the two brass conductors will be electrically connected through the conductive rubber and the metal foil.
Problem is that the brass oxidize and the surface stops conducting.
There is also a build-up of oxide on the conductive rubber strips. You might have heard that it is possible to get the aftertouch working by a modification to the sensor electronics. Only way to get the aftertouch fully working is by following the procedure below. This strip is not needed. Then loosen all springs.