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


#1

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.


#2

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.


#3

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.


#4

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!


#5

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.