Key contacts are the source of much headache on the Poly-61. Much has been blogged and posted by others about dis-assembly of the keybed, membranes, and maintaining clean key contacts. However in the case of THIS machine no amount of cleaning could bring back key functionality. I believe this is due to the membranes simply wearing out and the gold contacts losing much of their conductance. Replacement membranes are very expensive, and I wanted to explore cost-effective methods to milk the last bit-of-life from this keybed.
This repair involves re-coating the membrane contacts with a conductive pen, adding plastic shims to the keys, and replacing broken key bushings that have allowed the keys to sway too much side-to-side. The biggest disadvantage to this repair is a small number of keys are STILL un-responsive. Furthermore, re-coating the contacts in this manner will produce an effect known as bouncing. Bouncing is when a key is pressed it may send two, or several, note-on signals in rapid fire succession. This is because the contact, on its way to being fully depressed, will bounce several times on-and-off before settling. To me I can live with this more than have a dead keybed that does nothing. Anyway...on with the repair process.