Korg Mono/Poly

Thank you Laszlo, we will check your suggestions and will let you know. It is more likely we have a defective component which died due to capacitors replacement as now circuits run with the right voltage.

Will come back next days with more results.

--- In korg_mono-poly@yahoogroups.com, Laszlo Kovari <friendomatic@...> wrote:
>
> Good work, recapping and socketing always useful.
> Here are my thoughts:
> 
> 1. Set resonance to max for self-oscillation. Now you can control the pitch
> with the cutoff.  Set kbd track to max and play on the keyboard.
> The kbd track cv is generated from the same DAC as the oscillator CVs.
> If the noise comes from the DAC you can hear an instable pitch.
> This way you can be assured the noise is not from the oscillators.
> 
> 2. The DAC ICs are IC 10 and IC11. Type is CMOS 4069UBP, UBP means
> 'unbuffered', buffered does not work here.
> 
> 3. You mentioned it was good before recapping. Strange but cap type
> sometimes makes a difference.
> Once I replaced a 1 micro electrolytic to a foil cap with the same value
> and it made the circuit instable.
> Stay on the safe side and closely match the new components.
> 
> Laszlo
> 
> On Thu, Mar 28, 2013 at 8:20 PM, dir_marillion <dir_marillion@...>wrote:
> 
> > **
> >
> >
> > Hi,
> > We have the following results:
> >
> > Turning on the instrument. All knobs working great.
> >
> > When I press any key on the keyboard, on any octave and any pitch, with
> > filter or not (cutoff 100% - resonance 0%), with LFO(MG) or not, I listen
> > this note which comes together with a strange noise and it ends with a
> > pacman like sound.
> >
> > It has nothing to do with noise knob, which is also working, but it is
> > different than the "noise" I describe. It seems that this "noise" is a not
> > a ground like sound. Whatever is the waveform we select on any oscillator,
> > it seems like a sound that passes through the VCOs (all VCOs), so Monopoly
> > exports this strange "noise" sound on any key press.
> >
> > Technician has already replaced the following parts:
> >
> > 0. all capacitors on boards (including the power supply capacitors)
> >
> > 1. ssm2044 with a new one (which is tested and working on a polysix)
> > 2. tl072cn (put on socket)
> > 3. hd14051bp (DAC)
> > 4. all the chips on sockets (on cpu board) with exact the same chips
> > versions
> > 5. cpu D8049C-217 (which is tested and working on a polysix)
> >
> > has already checked the VCO chips and they have the appropriate
> > temperature while Mono/Poly is working.
> >
> > has already checked all board connectors/cables and they are ok
> >
> > capacitors have been checked and they are all with correct polarity
> > installed
> >
> > volts on cpu board are just
> >
> > no cut lines can be seen as all circuits are in very good condition
> >
> > when portamento is at full, it seems that the "noise" comes smoother with
> > lower volume.
> >
> > Thank you for helping me.
> >
> >
> > --- In korg_mono-poly@yahoogroups.com, "dir_marillion" <dir_marillion@>
> > wrote:
> > >
> > > Hi Laszlo,
> > > Thank you for your message.
> > >
> > > I have already forwarded your steps to the Technician. He will probably
> > check them during next week and I will let you know the results of course.
> > >
> > > --- In korg_mono-poly@yahoogroups.com, Laszlo Kovari <friendomatic@>
> > wrote:
> > > >
> > > > 1. Set osc volumes to min and check the noise issue with open filter
> > and
> > > > vca. This way you can detect whether problem relates to vcf+vca or
> > > > oscillators.
> > > > 2. Check board to board connectors. A loose connector situation can
> > cause
> > > > instability.
> > > > 3. Probably the DAC makes the noise, "pacman" like sound -> instabile
> > CV to
> > > > oscillators. Check if all 4 oscillators involved in the issue or just
> > one.
> > > > 4. Maybe a bad cap-polarity? Double check your recapping work.
> > > > 5. Recapping makes sense in my opinion. I recapped the power supply
> > and the
> > > > vcf+vca board in my MP. Electrolytic capacitors have a 2000-3000 hour
> > > > lifetime before they go out of specification. Out of spec means they do
> > > > their jobs less and less effectively, sound becomes degraded and noisy
> > over
> > > > years.
> > > >
> > > > Laszlo
> > > >
> > >
> >
> >  
> >
>