Korg MS-20 stuck knob fixed!
2010-01-12 by mrbfrankus
Hello, I joined this group to find a fix for a stuck knob on my MS-20. Well I went a head and fixed it before getting approved so I thought I'd share my experience for all you MS-20 owners who may run into this problem. One night I was having too much fun running beats through the filters, playing a drum machine with my right hand while my left had was tweaking the HP and LP filter knobs. I had my hand placed with a finger against each cutoff knob so I could turn both knobs simultaneously. This was a bad idea. I believe the sideways pressure from my finger on the pot shaft allowed some debris to shake loose and lodge inside the shaft, the LPF cutoff knob rotation was nearly frozen solid, S H I T ! ! I tried to twist it loose but that just made it worse until I was really forcing it and decided to back off. However I did notice that the filter cutoff was still responding to the small turns I was able to make & that it was purely a mechanical failure of the pot shaft. The main culprit in this case was 30 year old dried up pot lubricant. Upon closer inspection it looked like old graphite grease or dirt that had caked into fine grit sandy substance all around the rim of where the shaft enters the pot housing. Eventually I desoldered the pot, pried open the casing, blasted the whole thing with Deoxit, and re-lubed the shaft with axle grease from my local auto shop. Now it works like a charm! That's fine and dandy but after the repair I was left with the impression that it could have been alot easier without desoldering the part.. First thing to try: 1. Remove the knob from front panel, sometimes they will be held onto the pot shaft really tight, I had good luck using an IC puller to remove it without damaging the plastic 2. Spray the junction of the pot shaft and casing with Deoxit, use a paper towel or something to surround the part so the Deoxit doesn't run all over 3. Put the knob back on and turn back & forth, gently at first but you may need to use more force as I did to finally get it to loosen up. If this works you are golden! 4. Since the Deoxit likely has washed much of the old lube away, the 'clean' pot shaft will feel a bit gritty as you turn it. Remove the knob again. To re-lube the shaft I pressed some graphite axle grease on the edge of a dull razor as I turned the shaft to work it in there. Do that a few times until it feels better, cleaning up after each application so it doesn't get messy. Done! If that didn't work: 1. Using the service manual diagrams for reference, open her up & desolder the frozen pot using a spring-loaded desoldering pen. Do not try and use a crappy bulb or wick! maybe its just me but I always end up ruining something with those tools, the pen is so much better. 2. With the part out you can either replace it or really go to town trying to loosen it up with Deoxit & pliers. That's what I did and now I have the original part working good as new. 3. If you need to clean out the internals of the pot, read these links: http://www.michaelshell.org/gadgetsandfixes/fixingscratchypots.html http://www.geofex.com/Article_Folders/potsecrets/potscret.htm Since I had it out, I went ahead and cleaned the pot inside as well. I hope this helps someone down the line, thanks. - Brian