Wed Sep 3 16:35:06 CEST 2008

Taking apart the Roland MC-303

The idea is that I'd like to replace the motherboard with something
else, turning the box into a controller, and turn the motherboard into
a MIDI sound module.

Let's see if the user interface can be cleanly separated from the main
board.  At first sight it does look like it: there are 2 separate PCBs
for the top keyboard panel and the back panel with MIDI+AUDIO IO

What follows is what I can figure out just looking at the board.

Taking it apart:

* remove back and bottom screws. leave the legs alone, they are
  attached to the bottom plate.

* unscrew the mainboard (4 edges)

* to remove the PANEL BOARD: disconnect 2 connectors so the mainboard
  and panel board can be unfolded.

* remove knobs + gently pull off the big rotary knob, it is attached
  to the panel board.  DON'T push the buttons with the panel board
  removed, since this will make the glue come off.  also do not remove
  the dark screen, there's nothing there but glue.

On the panel board I count 16 screws in total: 9 that attach to the
chassis at the edge, and 7 that attach to a metal part that seems to
be glued to the main chassis.  Two of those are below the CPU board.

Picture 1: Bottom plate removed, all connections intact.

Picture 2-3: Jack Board unscrewed and exposed.

Picture 4: Main board.


74HC04AP  hex invertor for midi
PC910     optocoupler for midi

4 x C4570C  NEC opamp
5218A       dual low noise opamp

pins con  function
4    CN5
5    CN6  volume knob  (to PANEL BOARD CN3)
9    CN7  digital + power ?  (to MOTHER BOARD CN1)


2 x 74HC138AP  3-to-8 Line Decoder
1 x 74HC245AP  Octal bus tranceiver; 3-state

pins con function
5    CN3  volume knob (to JACK BOARD Cn6)
10   CN4  7x analog rotary knobs, 2 x GND, 1 x KNOB V+  (to MAIN BOARD CN2)
10   CN1  digital (to MAIN BOARD CN4)
12   CN2  digital (to MAIN BOARD CN3)

Looks like most buttons have an associated LED.  I don't see any load
resistors though.  Each switch has a diode in series.

The source drivers are connected to the line decoders, and to the low
end of the switches through a diode.  The other end of the switch
connects to a pull-up resistor and goes into the tristate.

The tristate is also connecteded to the source drivers, which drive
the leds into the sink drivers.

service manual

That's a lot more convenient: MC-303_SM.pdf from

Looks like i missed the 22R resistors connected to the source drivers.