Forgot to take a picture, I’ll do it next time I get one in…


Tuning instructions in the service manual are actually just fine. These are marginally easier to follow.

What you need

  • A tuner that shows what note you’re playing, such as a guitar tuner. I use the Peterson Strobostomp.
  • Digital voltmeter (DVM) for Key Assigner board (KLM-356) CV tuning
  • Ordinary very small screwdriver, a little bigger Phillips screwdriver
  • Speakers


  • Turn on your Mono/Poly, wait 10 minutes for warm-up
  • Pitch Wheel = center, Modulation Wheel = 0, EFFECT = disabled
  • VCO 1-4 TUNE potentiometers = centered
  • Enable UNISON, set DETUNE = 0
  • CUTOFF = 10, RESONANCE = 0
  • Set VCO 1-4 LEVEL = 0
  • EFFECTS = Off

Step by Step

Step 1 – Key Assigner (KLM-256) CV

Connect the positive lead of your DVM (using a hook clip) to the right side of R8. Connect the DVM ground to GND at jumper wire J12. Short-circuit the so-called TUNE POINT.

The red crocodile clip to the left is shorting the Tune Point pins

On this particular Mono/Poly it was not possible to reach the correct values in the following procedure. Since there wasn’t time to troubleshoot KLM-356 I guessed at some other values and compensated in the next tuning step [Step 2 – KLM-398]. I’m not sure external CV input would work as expected, but it was secondary as the synth had to be ready for concert fast.

  • All measurements are made at the right side of R8
  • Move TRANSPOSE switch to UP. Aim for 10.583V, using VR-1 (I used 10.500V)
  • Move TRANSPOSE switch to DOWN. Aim for 0.000V, using VR-2 (I used -0.020V)
  • Move TRANSPOSE switch to NORMAL. Aim for 5.250V, using VR-2 (5.220V)
KLM-356 trimmer positions

Step 2 – Condition & Compensate (KLM-398)

The Key Assigner’s pitch voltages are conditioned once more before reaching the VCOs. This is done on the piggyback board KLM-398. Instructions can be hard to follow – it’s almost diabolic how Korg labelled the trimmers in relation to the voice numbers.

Don’t use the (faulty) service manual instructions. The above image has the clues.
And here it is in plain writing. Pink numbers are [VCO number] test points and trimmers
  • Remove the shorting clip on the KLM-256
  • Press lowest C (probably unnecessary step)
  • Voice 1 (in pink marking): Measure pin 6 on IC1 and turn VR-2 for 0 volts
  • Voice 2 (in pink marking): Measure pin 2 on IC1 and turn VR-1 for 0 volts
  • Voice 3 (in pink marking): Measure pin 6 on IC2 and turn VR-4 for 0 volts
  • Voice 4 (in pink marking): Measure pin 2 on IC2 and turn VR-3 for 0 volts

Step 3 – Tuning VCO 1-4 (KLM-354)

Remember: DETUNE = 0, all VCO TUNE = centered all modulation off, KEY ASSIGN MODE = UNISON

VCOtTrimmer positions


Set VCO 1 LEVEL = 10

ActionVCO 1 OCTAVE switchHold down keyAdjust
116′Lowest FVR-103
216′Highest CVR-102
Repeat 1-2
32′Lowest FVR-101
42′Highest CVR-104
Repeat 3-4
Repeat 1-4
VCO 1. Compare the trimmer positions to the image, they are not where you might expect


Set VCO 1 LEVEL = 0. Set VCO 2 LEVEL = 10

ActionVCO 2 OCTAVE switchHold down keyAdjust
116′Lowest FVR-203
216′Highest CVR-202
Repeat 1-2
32′Lowest FVR-201
42′Highest CVR-204
Repeat 3-4
Repeat 1-4


Set VCO 2 LEVEL = 0. Set VCO 3 LEVEL = 10

ActionVCO 3 OCTAVE switchHold down keyAdjust
116′Lowest FVR-303
216′Highest CVR-302
Repeat 1-2
32′Lowest FVR-301
42′Highest CVR-304
Repeat 3-4
Repeat 1-4


Set VCO 3 LEVEL = 0. Set VCO 4 LEVEL = 10

ActionVCO 4 OCTAVE switchHold down keyAdjust
116′Lowest FVR-403
216′Highest CVR-402
Repeat 1-2
32′Lowest FVR-401
42′Highest CVR-404
Repeat 3-4
Repeat 1-4


Done. Turn up all VCO LEVELS and play in Unison. Use DETUNE to detune the four oscillators for fat sounds. It should be possible to get a very accurate tuning over a range of five octaves or more. It’s a very exact synth.

Sign In


Reset Password

Please enter your username or email address, you will receive a link to create a new password via email.