Check IC28, C36; maybe IC25 or IC29.
The multiplexed VCO control voltage (= proportional voltage to key
pressed on the keyboard) is demultiplexed to the six voices by IC25.
Each voice has a hold amplifier associated (IC26-IC28, C31-C36).
For VCF common processing (EG, VCF modulation, etc.) it is again
multiplexed by IC29. This is done with a free-running clock, generated
by IC11, IC12 and surrounding circuits. If the KBD Track knob does not
affect voice #5 then probably one of the multiplexers (IC25, IC29) or
the hold amplifier (C36, one half of IC28) is bad. I expect that the
EG Intensity knob and the VCF modulation is not working with this
voice as well.
You can measure with a DVM on IC29/pin5 and IC25/pin5. There should be
about the same voltage, which should change with the KBD Track knob.
If the voltages are different, C36 and/or IC28 are defective.
If the voltages are the same but do not change with turning the knob,
IC29 is defective.
If the voltages are the same and do change with the KBD track knob,
I would go for IC25.
Good luck!
Johannes
On 2013-01-07 14:10, del_poolp@hotmail.com wrote:
> Hi,
>
> the KBD Track rotary knob do not work on last voice on my polysix ... do you have an idea of test points for detect/repair it ?
>
> Thanks,
> Richard
>
>
>
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