Hi,
Today I reopened the case and boards but I couldn't touch the TL chips. I am afraid that my skills are not too good to proceed unsolder it, without causing any damage.

The only I could do was to replace the both 4066 chips (just in case) which were sockedted and then to tune the VCO4 with the method you suggested.

The 4066 chips did not solve the issue with the portamento on VCO4, but the VCO4 tuned perfect, so now all the VCOs are perfectly tuned.

During the procedure, I checked all the Portamento pot lines, with a polymeter and they work.

So, in order to solve the issue with the Portamento on VCO4, I have to take it and go to the electronic shop, to replace this chip which is located under the capacitors (extra work has to be done).

Finally, I noticed that when I turn on my Monopoly, some times (not all, a random note is playing without any key pressure. I have to tell you that about 2 weeks ago, I opened the keyboard and replaced some rubbers with new ones and cleaned the others with a soft alcohol.
Strange

Thanks

--- In korg_mono-poly@yahoogroups.com , "dir_marillion" <dir_marillion@...> wrote:
>
> Hi Florian,
> Your information is valuable !!!!!!!!
>
> Thank you very very much.
>
> I will follow your steps tomorrow morning, as I think you have almost explained me everything. I will also tune the VCO4 as you described, (the simple way to change the offset with VR402).
>
> --- In korg_mono-poly@yahoogroups.com , Florian Anwander <fanwander@> wrote:
> >
> > Hello
> >
> > Am 09.03.2012 14:24, schrieb dir_marillion:
> > > Is the TL072CP under the capacitors (inside the circle)
> > Yes. There are two, but the one which affects VCO4 is under the second
> > bentover capacitor (counted from the bottom of the circle).
> >
> >
> > > Do you suggest to replace the TL072 or I may have a damaged 4006
> > There is a basic principle of search for faults: never change two things
> > in the same step.
> >
> > So the order of steps should be:
> > * Replace IC10 (TL072)
> > * Check the portamento of voice 4
> > * If it does not work: check the fourfolded portamento potentiometer, in
> > case of doubt shortcut in each layer of the potentiometer the two outer
> > contacts
> > * Check the portamento of voice 4
> > * If it does not work: insert a cable into the portamento socket (this
> > switches the 4066).
> > * Check the portamento of voice 4
> >
> >
> >
> > > Second question. As VC04 is also detuned about 4 notes and I do not
> > > have the KLM398, which are the switches for the 4rth VCO that I have
> > > to tune I show two white circle tuners under the fourth VCO (check
> > > my uploaded picture).
> > You don't need KLM398, but only KLM354. I described the tuning procedure
> > in detail at http://fa.utfs.org/diy/korg_monopoly/vco_adjustment.html
> > I would NOT do the full procedure, but simply try to change the offset
> > with VR402
> > See
> > http://fa.utfs.org/diy/korg_monopoly/mp_16_klm_354_layout_TRIMMERS.jpg
> > the most left light green marking at the bottom named with "tune offset"
> >
> > Florian
> >
>