My Polysix is sick, any doctor?

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Joined: Tue Nov 23, 2021 1:47 pm

My Polysix is sick, any doctor?

Post by Alinae » Tue Nov 23, 2021 1:54 pm


My Polysix just catch a cold after a gig outside and the cutoff in correlation with LFO for some strange reason acts weirdly.

Basically, as long as the cutoff is up, no problem but as I bring it down it slowly start to sound distorted and then suddenly cut the sound for good. At this exact moment the LFO LED slows to it's minimal speed setting. Here a short video of what is happening:

I don't understand how these two elements could interact with each other. I'm okay for reading schematics, testing and solder some stuff but I have to admit that the Polysix schems are beyond my capabilities. If you had to follow your intuition, what would be your first guess?
Because of the architecture of the Poly6 (6 voices with each a VCF) my guess is that the VCFs are ok but that the potentiometers/control board might have suffered.

I have to say that the battery has been taken care of and shouldn't be the reason of this problem.

Thank you so much in advance for your expertise!

What I already checked (here are the schematics ... manual.pdf :
- No Voltage drop so far on the +/- 15V and +/- 5V

- As I'm checking CN11 I'm a bit confused, on one side (KLM 367 - Main board), I have Ground and Data (pin 1 and 2) and they seem to go in the same cable protection but never actually touch. On the other side, (KLM 369 - Controller and stuff) only the Data comes out. The ground stops a few centimeter before the CN11. Is it standard? A way of filtering interferences or something like this?

- I removed the battery since long ago and there are no signs of corrosion

- Connection between IC18/IC19 and IC 22 are ok

- IC 22 and 23 seems fine

As I mentionned, the synth started acting weird after a gig on a mountain, it was cold and a lot of humidity.
Any clue?

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