Oberheim OB-Xa Momentary switches

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Jacob Hunt
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Oberheim OB-Xa Momentary switches

Post by Jacob Hunt » Sat Jun 21, 2014 7:59 am

My manual and LFO sine switches both quit on the same night. Does this sound like a multiplexer or IC type problem, or just an old fashion switch problem? Does anybody know a way to test the switches, or just have an idea what might be happening? I've fixed pots by switching 4000 series chips on the pot board, but that's not gonna do it for the switches
Thanks in advance

P99
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Re: Oberheim OB-Xa Momentary switches

Post by P99 » Tue Jul 29, 2014 12:57 pm

Hi.
I'm afraid your switches are dead.
Since they're not on the same column/row of a mux and have the same age as mine ( DX and OBXa ), I suppose your only chance is to take the circuit off the panel, gently remove the switch cap with 2 screwdrivers, one left and one right and then lifting it, sand the silverplated ( sigh!! ) contacts with 800 sandpaper and put the caps on again.
Now you should be ok.
Just test them before : a multimeter with a beeper connected to the 2 pins of the switch should sound if the contacts
are ok. Try it 2 or more times.
If it beeps than it's ok and you have to search elsewhere.
If they do not beep, prepare to remove the knobs, the nuts and then unassemble the switches as described before.
I just desoldered ALL off my 2 oberheim DX switches, removed the caps and cleaned with soap and water, sanded all the contacts, changed some burnt out leds.........and theyr resistors!!!!!!!( they were too bright! ), reassembled and resoldered : long job but now both work like new.
Enjoy and Good luck
Bye.
Mick

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Re: Oberheim OB-Xa Momentary switches

Post by Steve Jones » Tue Jul 29, 2014 1:23 pm

I would suggest avoiding sanding a plated contact, once you remove that plating the switch will never be the same again. Best to clean the tarnish off the metal without taking off the layer of plating.
Synthesizer service tech since 1982.
Synth parts and service, Sydney Australia.

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synthparts
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Re: Oberheim OB-Xa Momentary switches

Post by synthparts » Tue Jul 29, 2014 9:31 pm

I have some working switches if you'd rather just replace them...
Vintage Synth Parts - http://www.synthparts.com

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