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Korg MS-20 restoration
Old 2nd March 2010
  #1
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Don Solaris's Avatar
 
4 Reviews written
🎧 10 years
Korg MS-20 restoration

Quote:
Originally Posted by jonnypowell ➡️
Any chance u could do a detailed lost on sevicing the MS-20 Mr Solaris?
Tries taking it apart but it seemed a lot more complex than other synths I've done minor repairs on. Really need to re-cap and clean the whole thing.
Remove two sidepanels + the bender section. Disconnect the bender section (wires) if you want.

Remove all the knob caps.

Remove all the bolts that hold the knobs.

On the section with jacks, there is another steel plate that has another set of bolts. Pain in the a**, i know. But you will have to do it once again.

And that's it. Take pics of whatever you remove. This will help you assemble. Good luck.

If lazy, just recap the synth board, the PSU (crucial part) is there as well.


Quote:
Originally Posted by Repoman ➡️
My question is about the re-capping is it wise to replace all Tants with electrolytic, and does anyone or yourself have a list of how many are needed and there vrespective values as I'm going to do the whole synth.
There are about 50 caps total. You should replace all the electrolytes and tantalums (important!) as these can die any day and cause a short-circuit. For tantalums use electrolytes with the same value - i think they are 1 and 10 uF. Only exception is the voice section where you should replace tantalums with tantalums.
Old 3rd March 2010
  #2
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golden beers's Avatar
 
2 Reviews written
🎧 10 years
if that's the same one that's widely available on the web (google ms20 service) then the circuit diagram is slightly different to the actual circuit in my MS20 (VCO section). i have the MK2 so this would bet the MK1 scema i guess! unless there are more revisions that i don't know about

dont ask me what's different! just be careful is all i'm saying.
Old 22nd March 2010
  #3
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Don Solaris's Avatar
 
4 Reviews written
🎧 10 years
Quote:
Originally Posted by jonnypowell ➡️
Hey Don I'm just replacing all the caps in the MS-20 now. Just want to conform that Im leaving all the ceramic one in and replacing the tantalum (green caps) and electrolytes with new electrolytes of the sam value.. Correct?
I don't remember tantalums in MS-20, but if you found some, ok, it would be good to replace them with tantalums (so that the value doesn't change much) because electrolytes have less tolerances in value.

As of any "green" caps you saw - these are not tantalums.


Quote:
Also is there anything else I can to improve the synth now that she's open (what a mission that was!)
Of course. The most important part. Take the vacuum cleaner (use just the pipe) and vacuum each potentiometer. Then apply contact cleaning spray on each potentiometer - you will notice horizontal hole on the front of potentiometer (looking from side) and small rectangular one on the back bottom. Decide from where you want to apply - from the side that is more easily accessible. Apply some spray on two pots, then twist them for about a minute. Then move to next pair etc. Dirty / scratchy pot is a common thing on MS-20. So do it properly.

Take care: you want to spray that inside potentiometer, not outside where it can reach the board.
Old 23rd March 2010 | Show parent
  #4
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Don Solaris's Avatar
 
4 Reviews written
🎧 10 years
Quote:
Originally Posted by jonnypowell ➡️
Should I stick these old caps back in now or replace them with new ones? Is it possible to damage caps from de-soldering I.e. Too much heat..?
If you replaced them with exact values, everything should be ok. Leave them as is. Heat won't damage them.

Could you take a picture of the caps you replaced?




Quote:
Originally Posted by jonnypowell ➡️
OK so I've clearly removed a lot of caps that were supposed to stay then?

What are the green caps? What is the massive orange cap on the underside of the main PCB?
Standard polyester / and or ceramic caps.

I can 100% tell you what they aren't. They aren't electrolytes. Have you read this before going into this expedition:

Capacitors replacement

You got a nice big picture of electrolyte capacitor.

We've been discussing electrolyte capacitor replacement here on forum for few years now. Plenty of threads on same matter. Electrolytic capacitor replacement in each one of them discussed.

Who exactly told you to replace all capacitors? I would like to know from where did you read that on our forum so that i can remove / erase the false information someone posted here. Not just because it misinformed you, but others as well.
Old 23rd March 2010 | Show parent
  #5
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nofi's Avatar
 
🎧 10 years
all good then!


Quote:
Originally Posted by jonnypowell ➡️
Just waiting on a response re Tantalum's??
low ESR electrolytics will do the job fine.
Old 23rd March 2010 | Show parent
  #6
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Don Solaris's Avatar
 
4 Reviews written
🎧 10 years
Quote:
Originally Posted by jonnypowell ➡️
BTW there were 3 tantalums in there.. I've taken those out so i'd be right to replace those with electrolytes yes?
Yes. That would be best. (though in general depending where on the circuit that is, as sometimes electrolyte which has greater deviation in actual capacity will do the job just fine - but when the value is critical and must be exact, use tantalum)
Old 8th April 2010
  #7
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jonnypowell's Avatar
 
🎧 10 years
Update on my MS-20 for those who are interested..
I replaced all the electrolytic caps and cleaned all the contacts etc and although it sounded amazing after-wards I still had the same problem with the scale switch on oscillator 2.
I contacted Triez and he recommended re-soldering the PCB joints on the problematic scale switch and now the problem is solved!
Such an obvious thing and I even noticed what looked like some cold solder joints which must have deteriorated over time.

Anyway, I'd like to learn more about simple synth servicing techniques to avoid having to send synths off in the future.
It would be cool if we could have a thread in here on calibrating synths, troubleshooting and using oscilloscope etc..
Anyone else with me here?
Old 8th April 2010 | Show parent
  #8
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oldgearguy's Avatar
 
🎧 15 years
If you really want to learn to repair gear, do the following:

obtain a good used DMM (digital multimeter). I use the Fluke 8060A, which has some good audio capabilities built in. Get the manual for it.

obtain a decent used dual trace oscilloscope (bandwidth isn't critical for analog gear - 20MHz is usually fine). get the manual for it.

Take any piece of analog equipment you have. Buy/download the service manual for it.

Now comes the hard part. Learn how to use those tools and simply measure various parts of the circuit. Use the oscilloscope to look at the audio at various points. Use a second tone generator (could be a digital synth) and feed both signals into the scope. Put the scope in X-Y mode and figure out how to use that to change the analog synth frequency to match the reference tone.

Use the multimeter to measure voltage, current, and resistance in parts of the circuit. Learn when to measure with the synth powered up and when to measure with the synth powered down.

Open the service manual for the synth. Study the schematics. Learn what resistors, capacitors, and diodes do and why they are in the circuit. Pull up the datasheets for all the ICs in the synth. Study the datasheets and understand what the ICs are doing and how they contribute to the way the synth works.

Do all that for a while and at some point you'll be able to start diagnosing problems, or at least being able to narrow down where the problem might be.

Keep notes about what you find. Consult electronics textbooks if needed. Practice tracing the signal flow and control flow in the gear. Learn the basics of power supplies. Remember to check mechanical failure points first (including fuses) before assuming its an electrical issue.

The internet is full of instant information. Knowing how, when, and where to apply that information cannot be downloaded. It can only be learned through repeated application and study.

20 years on and I still run into problems that kick my butt even though they usually turn out to be something relatively simple. I never had any EE courses (although I wish I did), but I do find that I get off on a tangent because I try to skip over the basics and jump into the middle thinking I know the answer without doing the basic legwork first. Not keeping good notes (because it was a one-off or a quick/simple fix) has also come back to bite me.
Old 3rd June 2018
  #9
Here for the gear
 
🎧 5 years
Tantalums in the ms-20

So, this is my first post here. I’ve been lurking in here since the early days of Gearslutz, and It’s been my number one resource for my gear-buing journey.

Anyway, I love the Korg ms-series, and have got an ms-10, and both a mk1 and a mk2 ms-20. I bought the mk1 last year from a japanese seller on ebay for a nice price, while I have had the other two for some years now. Although being in really nice cosmetic condition, the mk1 has a couple of minor issues, and I’m going to recap it (eletrolytics and tantalums) and clean it’s contacts. I had it open to inspect it shortly after i got it, so I know it has not been recapped earlier, even tho the seller said it had been professionally serviced. I also think the caps looked good, but I suspect this ms-20 has seen little use because of it's good looks. So dried-up caps maybe?

I used the partslist from the service manual and got my caps from Mouser (Elna and Nichicon for eletrolytics). But, the service manual lists three tantalum capacitors, and having studied all the drawings and pictures I could find of the pcbs I can only find two tantalums. I’m also not 100% sure what I should have bought here. There seems to be two big black tantalums in the vco-section. Those that I bought looks very different and are much smaller physically, but they have the correct values. This is the type I bought: https://no.mouser.com/ProductDetail/74-173D685X0035XE3
[/B]So, for those who have recapped their ms-20s, I’m curious as to what you have used here, and if anyone has found the third tantalum in their actual unit.
And should I also change the power regulators?


I’m sorry for the long post, but for those who are curious, here’s what’s wrong with my ms-20:

- The vco’s sounds like they constantly have a small touch of pitch modulation from a sinewave-lfo. But the speed of modulation is different on every key, and has nothing to do with the lfo. The speed is constant and does not change, so you could say the pitch instability is stable. It’s not really strong and is not allways noticable, but it is there. It's easier to notice with softer patches and with held notes. It’s the same when played with my mk2’s keys and via external cv, so the keyboard is ruled out.

- I know that every mk1 is quite noisy, but I think this one is a bit noisier than it should be. My ms-10, which is also quite noisy, is much more silent.

- In addition, this unit needs some warmup-time before it tracks well. My mk2 and ms-10 does not need this.

- The VCO2 scale knob is not 100% in tune, so when I change octave, i have to retune a little bit with the detune knob to keep it in tune with vco1. This could probably be more of a calibration case.


So these are the things that I hope a recap and cleaning will fix. Any suggestions?

Last edited by Armakuni; 3rd June 2018 at 05:28 PM..
Old 7th June 2018
  #10
Here for the gear
 
🎧 5 years
Hmm, no responses yet. So, I'll make a short version:
Those of you who have recapped your ms-20, did you replace the tantalums with tantalums or electrolytics?
Did you also change the power regulators?

And, does anyone know what electrolytic caps there are in the filter board in the ms-20 mk2?
Old 7th June 2018 | Show parent
  #11
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oldgearguy's Avatar
 
🎧 15 years
Quote:
Originally Posted by Armakuni ➡️
Hmm, no responses yet. So, I'll make a short version:
Those of you who have recapped your ms-20, did you replace the tantalums with tantalums or electrolytics?
Did you also change the power regulators?

And, does anyone know what electrolytic caps there are in the filter board in the ms-20 mk2?
FWIW, I always replace tantalums with tantalums.

If you have the machine apart and it has original regulators, you can always measure the ripple and change under load to see how they are behaving. Of course just replacing them without checking can be done.
Old 7th June 2018
  #12
Here for the gear
 
🎧 5 years
Thanks for the response. Will probably just change the regulators without measuring them.

Meanwhile I found a really helpful pdf which lists every component of the ms-20, not only a partslist like in the service manual, but also where on the pcbs they are placed. Maybe this could be helpful for others too: https://synthesizor.wordpress.com/20...al-parts-list/
(I hope the owner of the site agrees with me posting the link here).

Although, I still didn't find out what electrolytics there are in the mk2 filter board, I finally found out where on the pcb the tantalums actually are, without having to open the synth.
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