Korg Forums

Hi there,

So I've been modifying my MS20 (Kit) with some of the test points on the back of the voice PCB, as well as a few of my own. However, I've run into problems getting a lot of the VCO mods working. Here are my findings:

Osc 1 - all waveform outs pass directly through rotary switch. Therefore, wiring up individual waveform outputs was easy.
Osc 1 PWM - Modification works as expected (and sounds great may I add)

Osc 2 - Waveforms seem to pass through an analogue switch controlled by logic levels at the rotary. Individual waveform outputs are not accessible from the back of the voice PCB.

Here's where things get interesting/annoying:
Osc 1 and 2 outputs designated on the PCBs - no output.

Osc Sync - Input does not seem to work. Hardwiring the VCO1 sync out to the VCO2 sync in does absolutely nothing.

Osc 1 and 2 modulation inputs - Do not do anything whatsoever.

So what's going on Korg? Is there a cheat mode (akin to the key combination for switching filters) that we must enter to activate the test points? Did the designers unhook the above test points on the final run of PCBs?

Please note that I'm a competent synth builder and designer - I'm not a n00b with this stuff!

Cheers!
Fin Shakespeare

Thanks for the research because I would have ended up doing exactly your work.

B

I found exactly the same thing. Is there any word from Korg?

It's a shame, seeing how it's so clearly labeled. I don't really have anything to offer, but hopefully posting replies will get some attention. Any news?

I don't believe Korg participates here. I've never seen a reply from them on this issue.

Re Sync:

Looking at Auxrens findings on the MS20 mini, he added a diode to a switch and then soldered to the ms20 diodes.

Maybe all that is required for the kit version to work with the two solder points:

a couple of wires
a diode
a switch

http://www.auxren.com/2013/09/ms-20-min ... c-mod.html

Would like to know if that works before I open up my kit and do it myself!

I can then add pwm and VCO1 separate outs at the same time.

No, that does not work

Is there any new information regarding MS-20 Kit modifications?

I've seen a posting on an auction platform for an MS-20 Kit with a sync mod. It seems therefore such a mod is possible.

Is there any official information from Korg about those patch points on the MS-20 Kit's PCB? I wrote to their tech support in Germany about it but got no reply.

I think it'a a bit weird that there are all those clearly labelled soldering points on the PCB yet there is no information about how to use them.

To the OP: How exactly did you implement the PWM mod? Did you add an additional CV input for PWM?

The MS20M Kit desktop might have sparked an interest in modding our Kits, since we don't have the greatest MS20 anymore

any news about mods and patch points?

I'm attempting wiring of vco1 waveform outs, pwm and sync.

Any success mr white?

successfully installed pwm, had a look at the sync mod from auxren and remork, one installed on the mini, other on vintage.
I think we have to figure the pcb because the kit reissue is completely similar with the vintage

I added a pic of the VCOs of my Kit, you could see the transistor cluster right below vco1 pw and vco2 fine pitch pots.

from what I saw looking at vintage schematics, the trick with diode and switch is between Q2 and Q4

do not attempted yet because I'm not sure if I spotted Q2 collector and Q4 base correctly...

I tested that:

D4 sits between Q2 and Q3
D17 sits between Q17 and Q4

so I think that we should put the switch between Q2 pin facing down (collector?) and Q4 pin facing left (base?), any thoughts?

because, looking at the nod done on the mini it seems that the guy inserted the switch between the diodes, that in the kit were not the right connection...

here is the resource:
http://remork.blogspot.it/2011/11/korg- ... atics.html
http://www.auxren.com/2013/09/ms-20-min ... c-mod.html

there is something that still make me think..

diode.

in auxren mod, looking at where he soldered wires on diodes, he picked at the same polarity, as shown in the remork's vintage schematic.

with it in mind it seems that everything is reversed from what I fugured, so instead of Q2 and Q4 we shoud use Q3 and Q17?

Mr. White,

I appreciate your research. As an owner of an MS-20 kit, I am planning to open my synth up to add PWM and osc sync. I am very interested in how this thread develops as I would like to have a clear path to performing the osc sync mod before I pick up my soldering iron.

Also, having some MS-20M kit, envy, I am wondering if there is a way to add FM to the MS-20 kit?

Thank you,

Sjon

as no one takes the bill, I did

followed my clue tu look the schematics of the vintage korg and not the KIT board.

trick is between Q3 and Q17





it sounds simply awesome...