Fixing the MC-909 rotary encoder

aris — Mon, 05 Jan 2009 22:40:00 +0000

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 pt.no. 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.

SynthFrog » MC-909

Fixing the MC-909 rotary encoder