Oberheim 4-voice keyboard repair. One key seems to have a triggering issue

Hi, new member here.

I have an Oberheim 4-voice (Believe it or not, I’m the original owner). It seems to have recently developed an issue with one key on the keyboard. When pressed, it intermittently will do a thing where it jumps between the SEMs. I’m guessing this strange tracking behavior is some kind of physical contact issue. I’m a musician, not a tech so guessing is the right term.

Anybody have any ideas what might be the issue? How big of a job would accessing the keyboard mechanics be? Since they are basically on and off switches, I’m thinking it isn’t making a clean contact.

The contact for the gate is corroded. So the note triggers again and again. Since the OB4s keyboard algorithm is round robbin it will go through the four SEMs.

If I remember the contact mechanics right, then you should get a fibe glass pencil and clean the contacts with it.

Thank you so much. That makes a lot of sense. I’m guessing I’d need to remove the keyboard from the case to do this, is that right? I wonder what is involved in that. (Sorry, I’m a musician not a tech.)

It’s pretty awesome to be able to get advice on my 41 year old synth.

It’s a Pratt-Read key mechanism, and there are likely screws up from the bottom panel holding it in place (it’s been a while since I was inside of one of these). When you get it loose, flip the keybed over - but be careful of all of the J-wire contacts - you don’t want to bend them. There will be a bus bar or two running the width of the keybed, where all of those J-wires make contact, and it is these bars that probably need cleaning. We use DeOxit sprayed onto a cotton swab, but the pencil eraser technique works well too - I think a hard eraser like those used on some ink pens is best.

What a truly wonderful synth that Four Voice is!

Sam, thanks for the extra info! Once I can figure out the keyboard removal (And yes, I will be careful!) I do have DeOxit that I can use.

And I have to agree on how awesome the 4-Voice is. Believe it or not, I’m the original owner of this one.