Hi, I understood.

> Btw: it does not have to be the potentiometer itself. It could be >that the corresponding solder joint is corrupted.

I just re-opened the synth and checked all lines of the pot which correspond to the solder joints to the motherboard. No corruptions found. Will recheck.

The Synth is disconnected from power outlet and I am checking only if the lines are ok.

Of course I have not idea which line is for VCO4 and it seems that schematics do not show this detail...

--- In korg_mono-poly@yahoogroups.com , Florian Anwander <fanwander@...> wrote:
>
> Hi
>
> > Can you explain me a little how this pot works and what should I do
> > to test and/or fix it
> The working principle of the portamento circuit is very simple. There is
> an capacitor between ground and the control voltage line from the
> keyboard for the VCO pitch. If the keyboard control voltage changes,
> then its power will first be used to load the capacitor. This will take
> some time. So the voltage change will not be immediate, but will
> increase slowly. This causes at the VCO what we call portamento.
> (The same happens if the voltage drops. Then the unloading will take
> some time).
>
> As said, loading or unloading the capacitor always takes a little time,
> but if the CV comes with enough current (if the power is high enough
> (remember: power = voltage x current), then the loading or unloading of
> the capacitor is that fast, that our ear does not recognize it.
>
> The portamento potentiometer now simply acts as a variable resistor (so
> called rheostat) which is inserted in the CV-line before the capacitor.
> If the poti is turned fully counterclockwise then the resulting resistor
> is zero -> the capacitor will be loaded that fast, that we do not
> recognize it.
>
> If the poti now gets turned clockwise, the resulting resistor is
> increased -> the increased resistor means less current runs into the
> capacitor -> the capacitor will be loaded slowlier -> the pitch changes
> slowlier -> portamento.
>
>
>
> > Which is the line for VCO4 to shortcut and
> > how can do this
>
> I cannot tell you exactly which layer of this four layer potentiometer
> is the one for the VCO4, but I found an article in the web, which
> describes the principle of our problem quite good
>
>
> Have a look at http://www.allaboutcircuits.com/vol_6/chpt_3/7.html
>
> in the picture
> http://sub.allaboutcircuits.com/images/05151.png
> http://sub.allaboutcircuits.com/images/05150.png
> you have to think the battery as the keyboard CV and the motor as the
> capacitor. That is how the portamento potentiometer is wired.
>
>
>
>
> The picture
> http://sub.allaboutcircuits.com/images/05152.png
> describes, what might be broken in your portamento potentiometer.
>
> If you connect both the outer connectors of the potentiometer with each
> other, then it is like the potentiometers resistance would not be set to
> zero.
>
>
>
>
>
> > Does it contain graphite like the sliders on JX3p
> >
> Yes. All potentiometers work like that, but you can't repair it with an
> graphite spray!
>
> Btw: it does not have to be the potentiometer itself. It could be that
> the corresponding solder joint is corrupted.
>
> Florian
>