Discussion about the Korg PolySix synthesizer

Hi-
been working on a battery-damaged Polysix CPU board;  almost have it 
back in shape, except for one problem:  the LFO seems to be 
permanently affecting the oscillators.  I checked the switch logic & 
the inputs & outputs of IC 1 (the 4066 quad switch), and everything 
is as it should be (when the LFO to OSC is turned off, the switches 
cut off as they should) -- yet, the LFO is still somehow getting 
through to the oscillators.
Any ideas? (other than buying one of Crow's new boards?)

Thanks.

~GMM

Check the mod wheel circuit (not on KLM-367..is on KLM-369, I think).

Crow
/**/

On Tue, 2 Sep 2003, cavernosum6 wrote:

> Hi-
> been working on a battery-damaged Polysix CPU board;  almost have it 
> back in shape, except for one problem:  the LFO seems to be 
> permanently affecting the oscillators.  I checked the switch logic & 
> the inputs & outputs of IC 1 (the 4066 quad switch), and everything 
> is as it should be (when the LFO to OSC is turned off, the switches 
> cut off as they should) -- yet, the LFO is still somehow getting 
> through to the oscillators.
> Any ideas? (other than buying one of Crow's new boards?)

Hi -
thanks;  had a few minutes last night -- disconnected the wheels from 
the front panel (no help); disconnected CN06 - 2 (no help);  
disconnected R9 that feeds the CV mixer IC 8 :  problem vanished.

Didn't have any more time (dealing with a dead Prophet 5 power 
supply), but it's aroused my curiosity:  why would pulling R9 do the 
job, when pulling CN06-2 had no effect? -- according to the 
schematic, it would be basically the same thing.

Hope to have more time tonight;  meanwhile, any further thoughts 
would be appreciated.

Thanks again.

~G

--- In PolySix@yahoogroups.com, The Old Crow <oldcrow@o...> wrote:
> 
>   Check the mod wheel circuit (not on KLM-367..is on KLM-369, I 
think).
> 
> Crow
> /**/
> 
> On Tue, 2 Sep 2003, cavernosum6 wrote:
> 
> > Hi-
> > been working on a battery-damaged Polysix CPU board;  almost have 
it 
> > back in shape, except for one problem:  the LFO seems to be 
> > permanently affecting the oscillators.  I checked the switch 
logic & 
> > the inputs & outputs of IC 1 (the 4066 quad switch), and 
everything 
> > is as it should be (when the LFO to OSC is turned off, the 
switches 

> > cut off as they should) -- yet, the LFO is still somehow getting 
> > through to the oscillators.
> > Any ideas? (other than buying one of Crow's new boards?)

That is certianly strange.  The only thing I can note is the trace for 
the pitch modulation to CN06-2 does run right through the splash damage 
area of the original battery, so perhaps the trace got shorted or opened 
and is picking up noise from another part of the circuit.  Another guess: 
replace C43, which decouples noise on the pitch mod line from CN06-2.

Crow
/**/

On Wed, 3 Sep 2003, cavernosum6 wrote:

> Hi -
> thanks;  had a few minutes last night -- disconnected the wheels from 
> the front panel (no help); disconnected CN06 - 2 (no help);  
> disconnected R9 that feeds the CV mixer IC 8 :  problem vanished.
> 
> Didn't have any more time (dealing with a dead Prophet 5 power 
> supply), but it's aroused my curiosity:  why would pulling R9 do the 
> job, when pulling CN06-2 had no effect? -- according to the 
> schematic, it would be basically the same thing.
> 
> Hope to have more time tonight;  meanwhile, any further thoughts 
> would be appreciated.

Yeah, "strange" is my middle name.  Re-checked the traces several 
times & found nothing out of order;  might try severing all suspect 
traces at both ends & hardwiring (as a last resort).
Also want to look at the 4066 switch again (IC 1) -- will spend a few 
hours on it this weekend & let you know how it comes out
(so many synths to repair, and so little time!)
Thanks for your suggestions.

~G

--- In PolySix@yahoogroups.com, The Old Crow <oldcrow@o...> wrote:
> 
>   That is certianly strange.  The only thing I can note is the 
trace for 
> the pitch modulation to CN06-2 does run right through the splash 
damage 
> area of the original battery, so perhaps the trace got shorted or 
opened 
> and is picking up noise from another part of the circuit.  Another 
guess: 
> replace C43, which decouples noise on the pitch mod line from CN06-
2.
> 
> Crow
> /**/
> 
> On Wed, 3 Sep 2003, cavernosum6 wrote:
> 
> > Hi -
> > thanks;  had a few minutes last night -- disconnected the wheels 
from 
> > the front panel (no help); disconnected CN06 - 2 (no help);  
> > disconnected R9 that feeds the CV mixer IC 8 :  problem vanished.
> > 
> > Didn't have any more time (dealing with a dead Prophet 5 power 
> > supply), but it's aroused my curiosity:  why would pulling R9 do 
the 

> > job, when pulling CN06-2 had no effect? -- according to the 
> > schematic, it would be basically the same thing.
> > 
> > Hope to have more time tonight;  meanwhile, any further thoughts 
> > would be appreciated.

Finally got it working correctly -- bypassed CN06 entirely;  ran a 
line from the front panel to the mixing resistor for the CV summer, 
and everything is perfect.  While there were no shorted traces to be 
found, I think you may be right about noise proximity. Normally I'd 
want to know exactly what was wrong, but having a fully-functioning 
unit is enough for me -- now on to my other repair jobs.

By the way, would like to take this opportunity to publicly 
acknowledge your FINE Polysix repair site -- 
out of all the repair jobs I've tackled on various synths over the 
years, this is the only one where I had it all laid out, step by 
step, & didn't have to reinvent the wheel.
Thanks!

~GMM

--- In PolySix@yahoogroups.com, The Old Crow <oldcrow@o...> wrote:
> 
>   That is certianly strange.  The only thing I can note is the 
trace for 
> the pitch modulation to CN06-2 does run right through the splash 
damage 
> area of the original battery, so perhaps the trace got shorted or 
opened 
> and is picking up noise from another part of the circuit.  Another 
guess: 
> replace C43, which decouples noise on the pitch mod line from CN06-
2.
> 
> Crow
> /**/
> 
> On Wed, 3 Sep 2003, cavernosum6 wrote:
> 
> > Hi -
> > thanks;  had a few minutes last night -- disconnected the wheels 
from 
> > the front panel (no help); disconnected CN06 - 2 (no help);  
> > disconnected R9 that feeds the CV mixer IC 8 :  problem vanished.
> > 
> > Didn't have any more time (dealing with a dead Prophet 5 power 
> > supply), but it's aroused my curiosity:  why would pulling R9 do 
the 

> > job, when pulling CN06-2 had no effect? -- according to the 
> > schematic, it would be basically the same thing.
> > 
> > Hope to have more time tonight;  meanwhile, any further thoughts 
> > would be appreciated.