Korg Mono/Poly

Hello,
I recently acquired a mono/poly that has oscillator 1 out of scale.
I've read the calibration procedure in the service many and I'm not
sure if I am understanding it correctly. Aside from that, I believe
my primary issue lies with the trimpots on KLM-398 (i.e. VR1, VR2,
etc.). Assuming that I, in one of the ways I have tried to tune the
synth, am following the procedure correctly, then this must be the
issue. A brief note that I should mention is that my KLM 354 board is
not labeled so I assume that I am tuning with the correct trimpots
(VR10X) but I could be wrong. I am fairly sure that this is not the
case though. I am copying my post from another forum from here.

After literally hours of trying to do this, I've come to the
conclusion that I can proceed no further without some sort of help/advice.

I have been following this procedure and have had NO luck scaling the
oscillator.

First I tune A#4(Highest A#) with VR 102 at 16' to be exact (0 cents off).

Then I tune A#1 (Lowest A#) with VR 103 at 16' to be -5~-10 cents off.

Then I tune A#1 with VR 101 at 2' to be exact (0 cents off).

Then I am left with tuning A#4 at 2' with VR104 which simply does not
work, because, at this point, it is impossible to tune to A# at the
extreme of the trimpot.

While writing this I thought I may have reversed the tunings for VR
104 and VR 101 so I switched the which trimpot I tuned with and it
allowed me to tune all of the keys to A# as desired.

However, the keyboard is still badly out of scale. The first F is very
(+20 cents) sharp and it sort of flat on almost every note until a
certain note at which it goes sharp again.

I believe this problem to be with the trimpot VR1 and to be an effect
of the offset voltage not being +-0.1mV. However, I'm not at all sure
how to check this. I went to radioshack and bought a digital
multimeter which was a bad idea in that its lowest readable value is
0.1mv. Even so, I don't know where or how to verify whether the offset
voltage for the VCOs is 0.1mv (or even close).

Even if someone could please confirm that I am following the correct
tuning procedure I would be very grateful.

I also need to know how to "test the lead wire from KLM 398" to test
the offest voltage, but I will take any and all advice.

Thanks in advance.

Maybe you should contact a professional synth repair man. It will ofcourse cost a little, but
save your own time to a profitable work.

Yeah, I did that awhile ago but in the course of him fixing that problem another problem arose and I ran out of money so now I have to fix it myself.

Now I hear a constant FM like sound on the whole machine (especially when the cutoff and resonance are at maximum level).  I have gone over some of the machine with an oscilloscope and it is very obvious that something is wrong in the power supply.  I believe that a component has failed and is causing more something to try to draw more current than it should which is creating the noise.  So now I am changing the capacitors, op amps, and voltage regulators and if that does not work, then I am out of ideas.

Thanks,
Chase

envia94 <akva@hotmail.com> wrote:

Maybe you should contact a professional synth repair man. It will ofcourse cost a little, but
save your own time to a profitable work.




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Hi Chase

> should which is creating the noise. So now I am changing the
> capacitors, op amps, and voltage regulators and if that does not work,
> then I am out of ideas.

You might try to isolate the error also by disconnecting some boards,
and measure the rest:
'+++' means switch power on
'---' means switch power off

disconnect all boards
+++
check powersupply out with oscilloscope
---
connect KLM-356 (uP board) to powersupply and keyboard to KLM-356
(perhaps also the 353 with the keyboardmode switches is required)
+++
check the CVs at the connector pins 27-1 to 27-4 with oscilloscope
---
connect the VCO-board
+++
check the CVs at the connector pins 1,3, 9, and 11 of IC-7 with
oscilloscope.
check the outputs of IC-22 (opamp after Ext VCO in) with oscilloscope.
check at the four summing points for VCO-CVs
check the output of all four VCOs separately.
---
add VCF board
+++
Check again the output of the VCOs

and so on....

If the constant FM appears, the let the constellation as it is, but go
back in the measurement chain to check how far 'back' the FM can be
traced (e.g. already on VCO board, but not at the uP-board-output).

I don't remember wether the ICs originally are socketed. But if they
are, you might also remove some relevant ICs.

Florian

Hello,
    Upon the previous suggestion, I was able to get a bit closer to the problem, but still no solution.  However, I am hoping that my new information makes the problem easier to solve.

First, I replaced all the op/amps and it did not help.  After that, I tried various combinations of cables to see if I could eliminate the noise.  I was able to significantly reduce the noise by unplugging the orange cable from the CV board to the board with the LFO knobs.  Doing this almost eliminates the noise.  A noise is still there, but it is much quieter.  However, a click is present in the audio at max res and cutofff which happens at each cycle of the LFO.

It appears as if the LFO (s) and (most importantly) the arpeggiator are bleeding into the audio and creating much of this noise.  What could cause this kind of thing to happen?  Dead capacitors?  There are some capacitors on this board but I'm not sure what kind they are (polypropylene?).

I believe that fixing this bleeding problem will fix it all.  Any help is appreciated.

Thanks,
Chase Smith

Florian Anwander <Florian.Anwander@consol.de> wrote:

Hi Chase

> should which is creating the noise. So now I am changing the
> capacitors, op amps, and voltage regulators and if that does not work,
> then I am out of ideas.
You might try to isolate the error also by disconnecting some boards,
and measure the rest:
'+++' means switch power on
'---' means switch power off

disconnect all boards
+++
check powersupply out with oscilloscope
---
connect KLM-356 (uP board) to powersupply and keyboard to KLM-356
(perhaps also the 353 with the keyboardmode switches is required)
+++
check the CVs at the connector pins 27-1 to 27-4 with oscilloscope
---
connect the VCO-board
+++
check the CVs at the connector pins 1,3, 9, and 11 of IC-7 with
oscilloscope.
check the outputs of IC-22 (opamp after Ext VCO in) with oscilloscope.
check at the four summing points for VCO-CVs
check the output of all four VCOs separately.
---
add VCF board
+++
Check again the output of the VCOs

and so on....

If the constant FM appears, the let the constellation as it is, but go
back in the measurement chain to check how far 'back' the FM can be
traced (e.g. already on VCO board, but not at the uP-board-output).

I don't remember wether the ICs originally are socketed. But if they
are, you might also remove some relevant ICs.

Florian



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Hello,
    Upon the previous suggestion, I was able to get a bit closer to the problem, but still no solution.  However, I am hoping that my new information makes the problem easier to solve.

First, I replaced all the op/amps and it did not help.  After that, I tried various combinations of cables to see if I could eliminate the noise.  I was able to significantly reduce the noise by unplugging the orange cable from the CV board to the board with the LFO knobs.  Doing this almost eliminates the noise.  A noise is still there, but it is much quieter.  However, a click is present in the audio at max res and cutofff which happens at each cycle of the LFO.

It appears as if the LFO (s) and (most importantly) the arpeggiator are bleeding into the audio and creating much of this noise.  What could cause this kind of thing to happen?  Dead capacitors?  There are some capacitors on this board but I'm not sure what kind they are (polypropylene?).

I believe that fixing this bleeding problem will fix it all.  Any help is appreciated.

Thanks,
Chase Smith

Florian Anwander <Florian.Anwander@consol.de> wrote:

Hi Chase

> should which is creating the noise. So now I am changing the
> capacitors, op amps, and voltage regulators and if that does not work,
> then I am out of ideas.
You might try to isolate the error also by disconnecting some boards,
and measure the rest:
'+++' means switch power on
'---' means switch power off

disconnect all boards
+++
check powersupply out with oscilloscope
---
connect KLM-356 (uP board) to powersupply and keyboard to KLM-356
(perhaps also the 353 with the keyboardmode switches is required)
+++
check the CVs at the connector pins 27-1 to 27-4 with oscilloscope
---
connect the VCO-board
+++
check the CVs at the connector pins 1,3, 9, and 11 of IC-7 with
oscilloscope.
check the outputs of IC-22 (opamp after Ext VCO in) with oscilloscope.
check at the four summing points for VCO-CVs
check the output of all four VCOs separately.
---
add VCF board
+++
Check again the output of the VCOs

and so on....

If the constant FM appears, the let the constellation as it is, but go
back in the measurement chain to check how far 'back' the FM can be
traced (e.g. already on VCO board, but not at the uP-board-output).

I don't remember wether the ICs originally are socketed. But if they
are, you might also remove some relevant ICs.

Florian



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Change your electrolytics, maybe. I had to replace mine on my filters a
couple years ago.

If you're having global problems, maybe it's your power supply. Maybe
your caps are going there...?

Good luck,
Scott Deyo
The Bridechamber
contact@bridechamber.com
www.bridechamber.com

On Dec 26, 2007, at 9:21 PM, Chase Smith wrote:

> Hello,
>     Upon the previous suggestion, I was able to get a bit closer to
> the problem, but still no solution.  However, I am hoping that my new
> information makes the problem easier to solve.
>
> First, I replaced all the op/amps and it did not help.  After that, I
> tried various combinations of cables to see if I could eliminate the
> noise.  I was able to significantly reduce the noise by unplugging the
> orange cable from the CV board to the board with the LFO knobs.  Doing
> this almost eliminates the noise.  A noise is still there, but it is
> much quieter.  However, a click is present in the audio at max res and
> cutofff which happens at each cycle of the LFO.
>
> It appears as if the LFO (s) and (most importantly) the arpeggiator
> are bleeding into the audio and creating much of this noise.  What
> could cause this kind of thing to happen?  Dead capacitors?  There are
> some capacitors on this board but I'm not sure what kind they are
> (polypropylene?).
>
> I believe that fixing this bleeding problem will fix it all.  Any help
> is appreciated.
>
> Thanks,
> Chase Smith
>
> Florian Anwander <Florian.Anwander@consol.de> wrote:
>>
>> > should which is creating the noise. So now I am changing the
>> > capacitors, op amps, and voltage regulators and if that does not
>> work,
>> > then I am out of ideas.
>> You might try to isolate the error also by disconnecting some boards,
>> and measure the rest:
>> '+++' means switch power on
>> '---' means switch power off
>>
>> disconnect all boards
>> +++
>> check powersupply out with oscilloscope
>> ---
>> connect KLM-356 (uP board) to powersupply and keyboard to KLM-356
>> (perhaps also the 353 with the keyboardmode switches is required)
>> +++
>> check the CVs at the connector pins 27-1 to 27-4 with oscilloscope
>> ---
>> connect the VCO-board
>> +++
>> check the CVs at the connector pins 1,3, 9, and 11 of IC-7 with
>> oscilloscope.
>> check the outputs of IC-22 (opamp after Ext VCO in) with oscilloscope.
>> check at the four summing points for VCO-CVs
>> check the output of all four VCOs separately.
>> ---
>> add VCF board
>> +++
>> Check again the output of the VCOs
>>
>> and so on....
>>
>> If the constant FM appears, the let the constellation as it is, but go
>> back in the measurement chain to check how far 'back' the FM can be
>> traced (e.g. already on VCO board, but not at the uP-board-output).
>>
>> I don't remember wether the ICs originally are socketed. But if they
>> are, you might also remove some relevant ICs.
>>
>> Florian
>>
>>
>>
>> Yahoo! Groups Links
>>
>>
>>
>
> Never miss a thing. Make Yahoo your homepage.
>
>
>