[sdiy] Oberheim OB-Xa Servicing

[Stewart Pye]

Howdy,

I'm servicing a REV3 OB-Xa.
I've gotten to the upper and lower control board calibration section in the REV 3 service manual and am trying to do the first step:

DAC OFFSET ADJUSTMENT
Press the UNISON switch . Press low C (C0). Measure the voltage at pin 7 of IC#64 and adjust trimmer T6 (near IC#35) for 0.000V ±2mV.

I can't find IC64 on either of the control boards. From the schematic in the service manual U64 is part of a sample and hold circuit which also consists of a CA3080, and are fed by a multiplexer U47. I can find U47 on this board but there are only quad op amps and some capacitors nearby, and no CA3080. Is there a later version of the service manual to cover this PCB?

Serial number on this unit is 823706.

Regards,
Stewart.