Many folks love the sound of the MKS-20 pianos but find that their units distort when the velocity gets high or many notes are played. I was recapping and looking at the calibration and such and when i was done I still had the distortion problem.

I had read that the relay across the outputs was the source of the distortion. Rather than attempt to clean it or find a replacement, I simply removed it and jumpered the connections. I tested power-up with no relay *and in the limited testing I have done* I heard no loud pops or clicks.

In addition, the distortion was completely gone. I would always recommend turning down the monitoring system, muting input channels, etc when powering up gear, but so far, the MKS-20 seems well behaved and the distortion is gone.

My MKS-20 is back together and in the rack, so I'm reluctant to take it apart, but if someone else does this, please take a picture of the relay, the board with the relay removed, and after the jumpers are installed. If you have the service manual, it's pretty easy to determine which pins to jumper, but not everyone has it.

Finally - note that this is an alternate solution to tracking down a new relay that would be a drop-in replacement, which would result in an MKS-20 that is identical to the original units.

hi, mine has the same distortion sound problem, I desoldered the relay and it seems that it is very difficult to track a new one, do you remember which pins you jumpered?
Thanks

OK, since I didn't have my MKS-20 open (it's in the rack and all wired in and a hassle to get out and opened up again) I decided to take a couple pictures of the schematics and we can trace through it instead.

Looking at mks20_relay_1 first we see the signal coming in from the panel board on pins 18 and 20 (left side just below the big circled "3"). The relay is the dotted box labeled RL1. The signal leaves the relay and goes to capacitors C6 and C7 and then leaves the board via pins 16 and 17 of the small connector on the far right.

The relay normally routes pins 4 and 13 (the output pins) to ground (pin 6 and pin 9). The coil (curly thing between pins 1 and 16) is what causes the contacts to change over after the audio circuit is warmed up and stable.

To bypass the relay functionality, we need to permanently connect pin 8 to pin 4 and pin 13 to pin 9. Or in the larger view of things, we want to connect the incoming signal from connector pins 18 and 20 to capacitors C6 and C7.

Look at mks20_relay_2 now.

You can see the rectangle labeled RL1 and the larger connector to the right (labeled CN4) and the small connector to the left labeled CN3). The L/R orientation is flipped from the other picture because one is a logical drawing laid out to read left to right and this one is an actual circuit board layout showing the components laid out in the most optimal way electrically.

So, we're looking to connect pins 18 and 20 from CN4 to the capacitors C6 and C7 (located just above the relay). Follow the dark gray trace from pin 18 into the relay. Follow the gray trace from C7 into the relay. So, by connecting a jumper wire between those 2 gray traces in the upper right of RL1, you will connect pin 18 to capacitor C7.

Similarly, trace pin 20 into the relay and trace C6 into the relay. Note that by connecting a jumper between those two points in the lower right part of RL1 you will connect pin 20 to capacitor C6. You should end up with parallel jumpers running left to right from the middle of RL1 to the right side of RL1.

You should not have anything soldered into the 2 holes on the far left side of RL1 (near the diode labeled D7) that is for the coil and should be left unconnected.

Finally - since I did this relay jumpering as part of a larger overhaul (including recapping the unit and cleaning the volume control on the front panel) it will be interesting to see if the distortion you have completely goes away by removing the relay or if additional work is needed.

finally I just cleared the rl1 contacts (with a contact spray and a toothbrush) and it worked for me, the mks sound output is totally clear now. Thanks for the information, I'll try this permanent fix the next time the relay makes trouble again.

Would anyone know where I can find a service manual for the MKS 20? I am having the same distortion issues (just picked one up for $50 today). What did you use for contact cleaner (deoxit or something similar?).

Thanks in advance!

Here you go - help to keep these old beauties running

Thanks for that tip! Replaced and upgraded a lot of caps, too, sounds great now.

I think i need to do this to mine too, it def crackles when the volume is at 100%, but i put it at like 80% and it's fine

I have a different problem with my MKS-20. The chorus stopped working. I bought the MKS-20 to replace my RD 1000 (everything works on it but the action is beaten to a pulp).
I bought the MKS-20 instead of a P-330 because of the great chorus.
Has anybody else had this happen ? Any input on how to fix this problem would be greatly appreciated. This has me totally bummed.

Could be a lot of things. BBD chips, op amps, failing tantals, electrolytics. I recapped mine recently, sounds a lot better.

Wow... thanks for the quick reply.
I'm not a tech kind of person .... at all. In proof, everything you listed is greek to me. I was hoping for something like a bad solder joint or something else a dummy could fix.
I guess it needs to go to a tech, but I live in Bradenton FL, & I haven't found anybody in this area that really knows their stuff. I took a broken MKS-70 to the "Certified Roland Repair Technician" in the area, & he didn't have a clue. That unit is still sitting here broken & unused. I noticed, the last time I checked, he's no longer certified by Roland.
If you have any suggestions, or if you're a service kind of guy yourself, please let me know. Once again, thank you very much for the super-fast reply.

I don't have the schematics here right now, but it could also be a faulty relay. Any way, you need a qualified technician, not necessissarily from Roland though. One thing you could try is ask around at prodigy-pro.com 's forum.

Thanks again for another lightning-fast reply. I'll check out that forum.
I wish I was as good at fixing things as I am at breaking them.

The chorus circuit uses a few CEM3360 chips so one of those could have failed. I have them if you need one or I could even repair the MKS-20 if you wanted to ship it to me in Calif. I have repaired several of them before.

Hi
Thanks all for the info here. I had problems with crackles on my MKS (only on the piano patches), & it sounded like a bad ROM with a repetitive glitch is certain sample loops. Having worked in the chip industry for 30 years, I have never known a ROM or EPROM go bad, but sure enough, a single bit in my 15179738 ROM had flipped, so an 0x6A read as 0x6B.
This cost me the price of another MKS20 to discover, but at least I now have 2 working units.
I can post images of the ROMs if it is of interest to others. I searched high & low for images on the new, but drew a blank, so had to buy another unit to disect......

I picked up an MKS-20 today off Fleabay for AU$250, it is in decent condition with only a few marks etc, and it works. I do however have the dreaded distortion at full volume, but I also have a display that does not light up, can this be fixed easily enough?

Does the display work, but you have no backlight? If so, that's a common problem. Telesisgear sells replacement EL backlights.

Replacing an EL foil is not something I'd attempt if it was my first electronics project. The odds are you will damage the display and need a new one, which is a larger task to replace. It would be better to take the MKS-20 + new EL foil to a tech and ask him to do it and to either clean the relay or bypass it entirely. He could also do a PS capacitor replacement and a calibration. Then you'll have an MKS-20 that will last for a long time.

Or you can just leave it as-is and turn down the volume to minimize the distortion and spend AU $0 additional dollars on it.

Thanks for the info.....where can I get info on the EL Foil thingy, and Telesisgear please?

PS: And yes the display works fine, just the backlight that is not.

I think I might have found a place to supply the EL Foil, check it out:

backlight4you - EL-Panel, blue-green, 24mm x 96mm, laminated EL-Pbl-gr-24x96-sl

Is there another source you know of at all?

I can't check from work, but throw "telesisgear backlight" into google and you'll see their page. I've dealt w. them for a number of years (until I started replacing the displays with LED backlight ones and removing the inverter whenever possible).

Oh - EL is ElectroLuminescent which is the type of thin foil backlight used with LCD displays.

Found it, thank you very much for the info, appreciate it.

Since fixing this, I bought another broken unit. Backlight is easily fixed with "EL Tape" from Ebay. If the tape is too big, you can simply cut it to size as long as you don't cut through the contacts. I fixed 2 backlights for $10.

Also fixed the chorus, which was the normal problem with the MN3101 clock devices. Just measure the clock output & it should be around 48KHz. They often run fast when they break. I have seen the same problem on Boss Chorus units....

I've seen a couple of folk make an external IO into the chorus system on these things.
sounded pretty good.

Okay, so I have NO soldiering experience and I've never serviced any synth, however, I am worried that my MKS-20 I will be getting soon will have the same distortion problem. Could someone PLEASE make a tutorial video on the tools I would need and simply how to repair the unit if mine has the distortion problem PLEASE! Thanks!

I'm busy restoring an MKS20 now. I put in a CR2032 Holder and a new cell. I plan on:

- Bypassing the anti - thump relay

- adding a chorus input

- convert to 120v

- convert to a regular power socket

- new LCD or backlight

- where would you put the jack for the chorus input? I think drilling the back panel should be okay.

- Does anyone know the best method to do this, like a diagram or picture?

Would it be a good idea to add a mix control for mixing the chorus input with the MKS-20 signal. Where could you put the mix control?

- What about the tactile switches, they are an unusual shape.


PS Thanks to you for your uploads, they were very helpful.

Anyone have the service notes for the little brother of MKS20, the P330. I bought one that arrived dead, the display light turns on but no characters show, the MIDI activity lamp flickers when receiving MIDI, but no sounds come out. I opened it up and tried to reseat all connectors, but it looks Ok. I removed the battery to reset it, but no luck.

haha. you're about to travel to galaxies few have ventured into.

here's the guy who did it. there's also a basic example.
Studio and Technical log, La La Land Recordings Pty Ltd

I sort of wish Boz Labs would make a plug of this, but I doubt it's likely.
It sounds like they are crafted to be effective on certain kinds of sounds to me.

personally I'd consider a 9 or 15 pin female D connector on the back.
that way you can break in and out and maximise any configuration.

best of luck with it though.

@ depulse. I have a 330 but no schematics etc.
if you haven't changed the battery I would.
could be a dry joint or a failing cap maybe.

nice

Hello everybody. My MKS-20 has a problem in the chorus also (don't working) and tremolo only works if the chorus is turned on. Any tips? Thank's.

We now have a replacement for the AG2029 relay used in the MKS-20:
Relay, 5V - Syntaur

We had three of these in the shop recently - 3 out of 3 needed a new relay, and this got them working perfectly.