[sdiy] Oberheim OB-Xa Servicing

[Tony Kalomiris]

Hi Stewart,

I took a look at the service manual and indeed there is no IC64 (TL082) on the component overlay diagram but it's there on the schematic of the lower control board.

You can trace this KCV1 to the Voice 1, section Motherboard 'B13' 'C1'.

Tony K

On 2013-04-09, at 2:54 AM, Stewart Pye wrote:

> 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.
> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy