Korg Mono/Poly

Hi Guys,

I went through the tuning section of the callbration procedure for the
monopoly but ran into some issues.

Everything went as expected (e.g. read and adjusted the expected
voltages) but when it came to adjusting KLM-398 I found that VR-3 and
VR-4 were having no effect on the tuning for OSC 3 and 4 respectively.

OSC2 I was able to tune relative to OSC1 without a problem.

On top of this, OSC 3 is very out of tune. Adjusting the tuning knob
on the front panel to extreme values still will not put it into the
right range.

So a couple of questions:

1. Is it possible that the TL072 which is attached to VR3 and VR4 of
the KLM398 is dead?

2. AT the end of step 3 in the callibration procedure I am supposed to
adjust VR101, VR102, VR103, and VR104. I am assuming these are on the
other side of the PCB so I need to detach it from the front panel
(e.g. undo all the knobs and pull the pcb out) just to be able to
access the oscilator tuning?

3. At the beginning of step 3 it says to check the lead wires
connection points and make sure the DC offset is +/- 0.1mV.
Is this voltage measurement relative to each oscilator?
I was not clear on what actual votlage (e.g. between what points) I am
reading.

Your help is appreciated!


btw, I fixed that previous problem of the bad main output. It turned
out to be a problem with my patchbay!!(should have done better signal
chain trouble shooting)

So to update:

I can now see the holes in the pcb where I can reach the VR101, VR201
etc. (The lighting in my room is not so great).

However I still totally stuck with the Stretch tuning part. I think
the instructions are totally unclear.
I can't tune the other oscillators until this part is fixed.

If anyone can help me I greatly appreciate it!

cheers,
Danjel

So I finally figured out the stretch tuning system. I have to say that
the manual was terrible in explaining what needed to be done and it
was only from looking carefully at the schematic that I could figure
it out.

VR2 controls the voltage for OSC1, VR1 controls the voltage for OSC2 etc.

The signal you are measuring is at the connector (reading from left to
right) pins 2, 4, 6, and 8 and it is relative to ground.


There is also a mistake in the calibration manual for the next part.

The chart on page 1 shows the order of trimpots to tune for the VCO1 is:
VR102
VR103
VR101
VR104

but then on the next page it shows the order as this:
VR102
VR103
VR104
VR101

Which one do I follow??