Vintage Synth Repair

Hi,

After investigating a little bit more on this Polysix, I found out I have a second dead voice.
I can get some sound from these voices but it depends of the VCF settings. The KBD track knob doesn't have any effect on the defective voices.

There was a little bit of corrosion on IC23 (14051) so I replaced it but that did not fix the problem.
When I check the outputs of this chip with an oscilloscope, I can see that the KBD Track knob has no effect on the outputs of the dead voices. 
 
I also replaced IC12 (14024) and IC20 (4558) but that did not help.

Any Polysix guru out there could help me?

Thanks !

Nicolas



--- In vintagesynthrepair@yahoogroups.com, "Nicolas" <nico678@...> wrote:
>
> Hi,
> 
> Thank you for replying.
> I swapped the SSM2044 chip and the other chip on a IC socket but that did not fix the problem.
> 
> When I turn the EG Intensity knob full up I can hear sound from the defective voice at the same level as the other voices. I tried to find a trimpot for the EG Intensity but I coudn't find one. I guess there is a defective part in the circuit of that defective voice. I replaced the electrolytic capacitors but that did not help.
> 
> Any other ideas?
> 
> Thank you!
> 
>  Nicolas
> 
>  
> 
> --- In vintagesynthrepair@yahoogroups.com, John Henson <synthnerd@> wrote:
> >
> > Hi Nicolas,
> > I have found the SSM2044 filter chips to be problematic. I put tiny 
> > numbered labels on the chips and then swap them around to confirm the 
> > diagnosis. With the voice LED's it is easy to tell which voice is 
> > triggered. The envelope chips can sometimes be iffy as well but 
> > switching the VCA to gate mode will give you output if this is the case.
> > John.
> >
>