Discussion about the Korg PolySix synthesizer

I've just tested the effect board in another polysix. It does the same thing (volume drop). So the problem must be on the effect board.

I've done some tests today, but still haven't figured it out. I have traced the audio signal to pin 9 of ic15. At this point the speed potentiometer does not influence sound level. By IC 21 pin1 the sound level is effected. Weirdly pin7 of ic 21 voltage level changes when I move the speed potentiometer. I replaced ic21 but the results are the same. Not sure why vca mod would be changed by the effect speed potentiometer...this doesn't occur on the working board. Any thoughts welcome. Thanks

First thing is to check to effects board for acid damage. I've seen this
several times. Since the connector is located close to the battery on the
KLM367 any damage can also spill to the 368. I suspect this is even wors if
the Polysix was stored vertically.

To be honest: I don't like this blind guessing (Its like "I have an ache in the breast" - "yeah, my gradfather was wounded in worldwar two; the wound made him aches even years later. So check for a gun around you".... ;-) )

To get really honest:
There are two potential level controls on the effect board:
1. the patchlevel at the output of the FXboard
2. the resonance dependant level at the input of the FXboard

We first should check which one is influenced by the FXspeed. This has to be done by removing the original CV one after the other and replacing it with a replacing voltage (Resonance CN03-1, Patchlevel CN03-2).

By this tasl we should know which CV is the culprit. If this has not been done, it does not make sense to search any further.



Just for example: IC1, a CD4051, on the KLM370 panel board multiplexes the resonance voltage and the FX speed. Already there a crosstalk might happen - 4051 are well known to make inner ondirectional shortcuts when they get older (but this is only one out of many many potential places).



Florian
 


On 03.06.18 10:25 , Malte Rogacki gacki@gacki.sax.de [PolySix] wrote:

 

First thing is to check to effects board for acid damage.

Thanks for the advice. Firstly I tested this board again in a working polysix and the volume was still an issue (therefore it had to be on the elm 368 effects board). I checked one cv at a time. The effects speed voltage was crossing to IC21 pin7( patch level), altering the voltage. This board did have battery damage which I had previously cleaned. Not knowing what else to check I re-cleaned the battery damaged tracks. This gave a slight improvement. I then took out my etcher and etched inbetween all the damaged tracks and this fixed my problem. I initially was trying to remove battery damage, but I gather now that the battery leakage is also conductive. Is this correct?

On youtube you can find an interesting video by Golt! on battery leakage in
synthesizers and a little bit about the chemistry involved. The electrolyte
combines with the metals on the pcb, such as the copper traces, tin IC pins,
etc, so it's not just the electrolyte you are cleaning,

Glad you found the issue.

Super, thanks Bob I will check it out. I've tested the synth again tonight and all is good.