[sdiy] Oberheim TVS Keyboard scaling

[klosmon]

Thanks.  Turns out the problem was a couple of faulty unbuffered 4041s 
-- replaced those, and the circuit now gets the correct data.
The left trimmer is for the transpose/pitchbend knob;  the right trimmer 
is for the keyboard scaling.  Easy, once the unit is actually working 
correctly.

~GMM


On 7/30/2014 2:51 AM, Roman Sowa wrote:
> I would start checking all the 4030 gates in the keyboard scanner. If 
> one of them is faulty, few notes will play wrong tune while most of 
> the keyboard range is OK.
> Just my wild guess at this time...
>
> Roman
>
> W dniu 2014-07-30 09:29, gm pisze:
>> So I'm doing the usual SEM repairs on a Two-Voice --
>> get to the final testing stage & notice that, while the oscillators on
>> both SEMs track correctly in Unison mode, the two SEMs are several
>> semitones out in Duophonic mode.  Further testing reveals that while I
>> can get a three volt range from the bottom of the keyboard to the top,
>> the third C is flat (along with several keys around it).
>>
>> There are only two trimmers on the digital keyboard control module; does
>> anyone know the correct procedure for scaling this thing?  All supply
>> voltages (+/-18.5, +/-10, +9) are present and correct;  would like to
>> eliminate the scaling as a cause for this before I start looking for
>> other repair options.
>>
>> Thanks.
>> ~GMM
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