Fixing the MC-909 rotary encoder

And of course taking a peek at its guts to shoot some porn in the process:

This is the MC-909.. It is my favourite synth because it allows a hands-on approach to sound synthesis. Even if it is targetet to the DJ market (which I am not!), it is capable of very interesting textures (and it has a nice sampler even if it lacks the velocity and key multilayering of the high-end samplers)

I got it second hand from ebay and since day one, the rotary encoder had a slight problem. I had to turn it slow to register correct values. If I rotated it quickly it would jump 5-6 values behind every 5-6 values (so it didn't go anywhere).

I decided that I would fix it and gutted the machine.. pictures follow:

The faulty encoder can be seen in the following picture:

The pads are velocity sensitive and this is how it works: there are two contact areas
and the rubber pads have the graphite layer that correspond to these two areas in different heights. So when you hit the pad, the MC measures the time it took to close both switches which corresponds to the velocity of your hand.

This is the encoder. Close ups:

The part can be found at mouser as 688-EC12E2420802 (alps 12mm rotary encoder) and it costs only 2 bucks. It is very simple to replace it, you must have a solder pump though to cleanly remove it.

Things to remember:

*) when you unscrew the machine, make a note (NOT mental) to the whereabouts of each screw..
*) the order of removing the components is the following: 1. the PSU, 2. the IO board, 3. the sound engine, 4. the "DJ" slider (the big one), 5. the mains outlet and 6. the main board.

some connections (eg the one marked with x) need not be disconnected. You can put the IO board aside for a while.

Good luck if you have the same problem.

Good choice if you have an MC-909 instead of an MC-808 :)

Now my MC-909 is like new.


X said...

Thank you for this post. I recently encountered the same problem. After getting absurd price quotes for repair, i also thought i might try to repair it myself. I went so far as opening up my MC909 to the first degree, and then realized it was a bigger project than i thought at the time, due to the way the encoder is located (not easy to access).

Is Mouser's replacement part better quality, or the same as the replacement part Roland sells.

Your post will be VERY helpful when i re-attempt this procedure, especially the part about the "order of removing components."

What tools did you need for this job, other than screw set, solder pump, and soldering iron?

thanks for your response

Aris said...

Hi there,

the part I got from mouser is EXACTLY the same as the one it replaced.

I used an electric screwdriver to do the job because as you might have seen, there are MANY screws there.

I also used a marker pen (a black one) to draw a circle where the black screws were on the main board. They have different size and threading space from the golden coloured ones.

Even better, you may draw a layout of the board on a paper and when you remove a screw, put it on its relevant position on the paper layout.

The above is to stress the need of making a note of the positions of the screws as there are 4 types of different sizes and/or threadings.

You may also need a set of pliers to place/remove the flat cables that connect the different components.

Last note. I didn't completely remove the main board. I just raised it enough so as I can place the encoder. Removing it is an unnecesary overkill.

I ordered 3 rotary encoders from mouser so if you want, I could send you one (for free of course). (I will keep the other one, just in case...).

Hope to have helped a bit,


Hope to have helped.

Aris said...

X wrote :
"Same i guess it's prone to the same issue. well, i like my 909 too so i guess i should just get familiar with the practice in case it happens again.

i have been without the encoder/dial for quite some time now. it functions as long as i dial really slowly. however, in the meantime, i have grown accustomed to using the INC & DEC value buttons with ease. but i dont like knowing my 909 is busted, and sometimes my reflex still reaches for the encoder dial.

yeah first pass was rough enough, just getting under the hood of the 909 yielded so many screws.

your suggestions are very good. i like the idea of drawing a layout on paper.

for the record, this will be my first time soldering. do you suggest a bit of practice first? can a beginner handle this job?"

(removed his email address from the comment)