[sdiy] Oberheim 4-voice issues (SEM, keyboard)

[thx1138]

On 4/20/11 8:40 AM, "Eric Frampton" <eric at ericframpton.com> wrote:

>> I've seen 3086'es blow up before so i'd change it and see.
> 
> I tried swapping it out for a new one; no change in behavior.
> 
>> (ouch! hangover!)
> 
> Well-earned, I hope!
> 
>> but if both oscillators aren behaving the same, look for any components
>> shared by the two oscillators.
> 
> As best I can tell the 3086 is the only part that's shared.
> 
>> What kind of keyboard is it? Sounds to me like it's a j-wire two-bus system?
>> In that case, check for the wires under the affected keys and see if the wire
>> going to the gate bus might have been bent.
> 
> It's a special version of a Pratt-Read; every J-wire is sent straight to a
> separate input in a mux'ing system.
> 
> e
> 
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Hi Guys,

Having worked on and designed some of these devices I can tell you a bit
more detail.

The Pratt Read keyboard was designed by E-Mu for E-Mu, Oberheim and
Sequential Circuits. The PPG Wave 2.x units used the same keyboard.

It uses a single J-Wire buss to Muxing system in the analog Keyboard
controller.

I have schematics here on the entire system and can lend a hand if you are
local to Los Angeles area.

Regards,

Terry Shultz