MS20 Kit mod/test points non functional

[sjonp]

HI All,

I have finally started the sync, PWM and filter switch mods on my MS-20 kit yesterday. I have drilled out the front panel for the jack and switches. I hope to get the soldering done before the weekend and testing/reassembly over the weekend!

Thank you for all the helpful information!

Best,

Sjon Pelletier

[sjonp]

Hi All,

I finished my pwm, osc sync and filter switch mods over the weekend, including testing and reassembly. While the mods were fairly straightforward, it was an involved process between disassembly, drilling jack and hole switches, soldering, partial reassembly for testing and final assembly. I had one hitch where I didn't measure out enough wire distance between the filter switch and the three pin connector as well as learning how to properly set up a 3 pin connector (needed to crimp the metal pins to the wires and not just solder). PWM and osc sync sound great! I also like being able to switch the filters without powering on with a combination of keys pressed. I am really glad I got a few mods done in one shot, as I do not think I would like to take the MS-20 apart again any time soon. Thanks again to all the members who shared their knowledge, particularly Mr. White and Steve GG.

Best,

Sjon

[hoegge]

How did you make the PWM mod? I could not find any information on it in the thread.

[Spacecat]

May I ask how did you exacty do the PWM mod & the osc sync mods?

[sjonp]

Hi,

I do not check this forum frequently, so just seeing this inquiry.

For PWM, there are labeled points on the MS-20 Kit circuit board. If you do a search on Google you should be able to find images of the circuit board with labeled test points. Also, do a search on "MS-20 PWM mod". If memory serves me right, you can look at other topics within this discussion forum, where there is a string about these test points with images.

For parts, you will need a 1/4 inch jack, some wires and to drill out a 1/4 inch hole on the front panel. Before you buy the jack, I recommend disassembly of your MS-20 Kit and taking a picture of the jacks that are already installed on the patch board. I think it is a mono jack with three posts that need to be soldered to the test points on the circuit board with wires. It has been almost a year since I did this work, so the specifics are not so fresh in my mind any more.

Please note, that this mod is for the MS-20 Kit, not the MS-20 Mini.

Good luck,

Sjon

[sjonp]

Hello Again,

Regarding the Osc Sync mod for the MS-20 Kit, please go back in this string to Mr. White's post in May 2015. The information for doing the Osc Sync mod starts there and there is more information as you go forward on the thread. You will need a switching diode, a switch, a couple of wires, a hole drilled on the front panel for the switch to be mounted, and soldering skills. There are images in this string showing where you need to solder on the circuit board. There are also some links in this string to someone named "auxren" who did the Sync and the PWM mods on his MS-20 mini which provide specifics on the type of switch and diode. Again, I did this work a little under a year ago and the specifics are not fresh in my mind so I can only direct you to where the information is.

Best,

Sjon

[sjonp]

Hi,

Here is a link to a gearslutz forum string which has images of the test points on the MS-20 Kit circuit board:

https://www.gearslutz.com/board/electro ... ing-2.html

The relevant post is by Psychlist1972 dated 23 November 2014.

Best,

Sjon

[Spacecat]

thank you very, very much. This is helpful indeed!

[infindebula]

So just to confirm the functionality of the mods:

The PWM mod is a jack. Simply patch an envelope or LFO to this jack and it will modulate the pulse width?

The sync mod is a switch. Engaging it forces VCO 2 to sync to VCO 1. Applying a separate CV to via VCO 2 CV IN will cause wild timbral shifts similar to the classic osc sync effect?

Does anybody have any video or recordings of these mods?

Thanks

[crossby]

as no one takes the bill, I did Smile

followed my clue tu look the schematics of the vintage korg and not the KIT board.
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trick is between Q3 and Q17 Wink

[Mutiny in Jonestown]

Been putting this off for about a year and finally got around to taking a shot
at the infamous PCB mods yesterday. I saw a great youtube vid that really
helped...seeing how someone else did it first answered a lot of questions I
had. The YT vid can be found at:

https://www.youtube.com/watch?v=8BLToE3wv-Y

So I wired up 6 additional jacks connected to the PCB VCO1 out, VCO2 out,
LPF Rev 1 out, LPF Rev 2 out, HPF Rev 1 out & HPF Rev 2 out labelled points.
I didn't bother with the VCO In or VCA points since others have reported they
don't work anyway. Didn't do some of the other mods mentioned in this
thread requiring a diode or other components...just went for the simple
output points. The whole project took a couple hours at a slow and careful
pace.

Everything works as expected...almost

Now, with nothing patched, if I switch the filters from Rev 2 to Rev 1 VCO
output stops, but I can still get output from the filters self oscillating, but in
unexpected ways. Very weird, but the MS20 is my bizarre sound generator
so I like it

Here's a couple shots of the project...