I bought a Roland JUNO-D which had the problem that only 2 or 3 keys worked. A little googling showed that this JUNO-D wasn’t the only one suffering from this issue.
It seems that the keys just stop working after a while. Sometimes within two years of continuous operation the keys stop working one at a time. but I’ve also read stories that someone didn’t use it for 6 months, plugged it in and all the keys where dead..
I bought a Roland U-20 a while back with the same problem and cleaning the contacts underneath the keys fixed that problem. So I took the JUNO-D apart and started cleaning the contacts with Q-tips and alcohol. And again. And again. And again until about 50 keys worked again..
Cleaning just didn’t work here. The problem lies in the black carbon dots on the inside of the rubber contactstrips. They just don’t conduct electricity very well anymore. When you press a key the 2 carbon dots are pressed against the pcb with the gold contacts connecting the 2 semi-circles and you hear the tone.
As you can see the 2 carbon dots don’t have the same height so the first one touches the pcb slighty earlier than the second one: thats how the velocity sensitivity works. It can calculate how hard you pressed the key.
I ordered 5 new contactstrips from Roland (partno’s: 4 x 04230834 RUBBER SWITCH 12P FOR JUNO-D and 1 x 04230845 RUBBER SWITCH 13P FOR JUNO-D) for less than 25 euro’s. The replacement parts looked a little different. The color was different and the rubber pins that go through the PCB keeping it in place where about 70% shorter which made replacing them alot easier.
I bolted the whole thing back together, switched it on and everything worked like new. Hope this batch of contactstrips doesn’t go bad after a couple of years 🙂