[sdiy] Juno 60 memory button carbon contacts

[Rutger Vlek]

Dear list,

I'm struggling with repairs on the memory buttons on a Juno 60 which had a serious couple of decades of stage use. It's basically key cap, a holder a pair of contacts and a silicone-carbon disk contact system (dome shaped). I managed to get most of the buttons back to life, but a few of them are not working along. I cleaned the contacts in the switch (cotton stick and a bit of contact cleaner), I cleaned the carbon disks with alcohol. After several attempts I'm still measuring difference in the resistance of closed switches (nearly 0 ohms for those that work well, approximately 50 ohms for those that don't). The silicone of the domes seems to be in good shape. The carbon disks showed some grooves that mirror the contacts. After several failed attempts, I very very gently sanded a slight bit of the carbon disks to make them completely flat again. Still no improvement...

I'm looking into alternatives now, considering:

(1) finding replacement switches of the same time or replacement carbon-disk-domes. Neither showed up on thorough googling.
(2) buying new sealed tact switches. I found switches that fit the PCB, but can't find appropriate square caps that fit the dimensions (14.3x14.3) as well as being more or less the correct height.
(3) more cleaning? replacing carbon disks with ones cut off from a remote control? using carbon paint? using a pencil to add carbon? neither of these seems to me a reliable long-term solution

Any thoughts?

Personally, I'm surprised 50 ohms is not low enough to trigger the detection of a closed switch.

Regards,

Rutger

ps. Additionally, I'm looking for a missing Arp switch cap (orange, 3.2x3.3mm plunger clamp) and 8 fader caps. If anyone has those (or Jupiter 8 slider caps, which are identical) at a decent price?