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MS20 service questions
Old 9th November 2009
golden beers's Avatar
2 Reviews written
🎧 10 years
MS20 service questions

to fellow MS20 users.
so i'm going to open up my MS20 because it has no Osc2 output
couple of questions:

i have the MK2 and it seems that all the service manuals online are of the MK1.
anyone know of a MK2 service PDF?

whilst i'm in there i'de like to try and fix up the keyboard scaling - am using a Kenton box, which has all my other mono's locked perfectly across 6 or 7 octaves. the MS20 however doesn't like to play along and the scale goes out after about 4 octaves. any slutz know of an internal pot in the MS20 i can tune to correct this?

PS also thinking about adding the fabled PWM mod to it: ie adding a Jack socket to modulate PW value. any other sluts done this? i've read that the MS20 is set up for this, but they didn't have the space to add the socket on the front panel.

MS20 with PWM mmmmmmmmmmmm
Old 9th November 2009
Gear Addict
🎧 10 years
I always suspected the range & scale trims were what lies beneath the rubber grommets on the front panel. (i've never had to check, my Emma tracks beautifully and has the most stable VCOs of all my synths)

Go the PWM mod!! FTW!!!!!!!!!!
Old 9th November 2009 | Show parent
golden beers's Avatar
2 Reviews written
🎧 10 years
ah yes the grommets. doh!
i'll actually have a look at the service manual for a change.
Old 10th November 2009 | Show parent
Lives for gear
🎧 15 years
Yes, most adjustments are under the grommets, so setting tune offset and scale don't require opening the case. I have serviced maybe 9 MS-20's over the past year, and more than half had electrolytics that were showing some signs of leakage BTW. Not the easiest machine to work on due to it's case design, but quite straightforward electronically. Look for cracks on pot solder joints.
Old 23rd November 2009 | Show parent
golden beers's Avatar
2 Reviews written
🎧 10 years
thought i'de update you MS20 owning sluts on this:

the circuit diagram in the service manuals you'll find all over the web are all for the MS20 MK1, if like me you have a MK2 then the circuit is slightly different.

also the manual is missing the circuit diagram for the KLM-128C board, which is the main jack socket board.

as i've learnt (because of gearslutz) i have a MS20 MK2. this is identified by a small screw in the top of the AMP diagram on the front panel. i was lead to belive that this screw holds 'the MK2 filter board'. this is a myth, in fact the screw goes into the power supply IC board. the filter baord is under the main board.

my OSC2 not outputting was due to open circuit on the VCO 2 CV IN input jack socket. when there's no jack in there it's normalised to connect the keyboard or VCO 1 + 2 CV IN input jack with the OSC2 circuit.

when you put a Jack into VCO 2 CV IN it breaks the circuit to allow the jack to feed the CV to osc2. i fixed it by opening up the case and bending the socket tip back in a little so it closed the circuit. easy

if you have a osc2 no output problem remember to try a CV directly in to the VCO 2 CV IN input jack socket. if this makes the osc2 work then you have the same problem.

PS the PWM mod looks easy peasy, haven’t done it tho, didn’t have a suitable resistor on me, so this mod will have to wait.
Old 25th November 2011
Deleted 8456dd3
MS20 filter CV help?

Nevermind i figured it out- bad cables
Old 25th November 2011
Lives for gear
remote337's Avatar
🎧 10 years

If you are tuning an MS then as its Hz per volt there is no scaling on the front under the gromits. You just tune the top of the keyboard with the top on each osc and the bottom under the bottom gromits. The whole keyboard should then track.

I watched James Walker completely re cap service and calibrate mine last week.

I'm not saying you don't need to scale your pro solo but get the MS right first.
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