How to make your keyboard feel younger, by Murray Moffatt:
After pulling my old JR-100 out from the bottom of a cupboard where it had rested undisturbed for since the late 80's, I discovered that many of the keys didn't want to work.
If you have the same problem, here's how I fixed it:
(1) Remove the three screws on the underneath of the JR-100 and open the case like a
book. Be careful you don't pull the ribbon cable that connects the two halves too much.
(2) The keyboard section is clipped into the top half of the case. Push in the clips and ease the
keyboard section out of the top half of the case.
(3) Remove the thirteen small screws on the bottom of the keyboard section (you will need a jewellers Phillips-head screwdriver for this) and separate the two halves. One half contains the rubber membrane keys and the other half has the gold contacts.
(4) Using isopropyl alcohol and cotton buds you can clean the gold contacts (you may see a build-up of a black substance on the contacts, make sure this is all removed). Also clean the bottom of the rubber keys (i.e. the black circles that make contact with the gold contacts).
The black circles are actually painted onto the bottom of the keys with conductive paint, so inspect the circles carefully to ensure that no paint has worn off. If some paint has worn off then you can purchase conductive paint or ink from some electronics shops.
(5) Rebuild your JR-100 by following steps (1) - (3) in reverse. If you're lucky like I was you will find that all of the keys now work 100%!