Korg CX-3 (vintage) MIDI kit retrofit installation manual Vitalka Custom
This retrofit connecting directly to key contacts or SM304A shift register ICs. Required to solder 70 soldering joints.
Retrofit receives MIDI notes and triggering circuit boards the same as you playing on the keyboard with hands and triggering key contacts. It controls only the keyboard, all other controls in your hands and you still can play with the keyboard at the same time when it controls with MIDI.
Welcome to the metric system zone. Here we work with precision things and all dimensions are metric. 1" = 25.4mm.
Installation:
To your good usability select the friendly place to mount the LED, DIN5 MIDI connector, button and PCB. Mount connector, LED and button before soldering wires.
PCB can be mounted under the keyboard on the left side.
Drill holes and to mount it before soldering wires.
Drill dimensions:
DIN5 = 18mm.
LED indicator = 6mm.
Push button = 12.5-13mm.
Be careful with drilling hole for button, it have small range to get hole too big.
Board dimensions and distance between screws:
Board dimensions 102x50mm.
Holes distance 94x39mm - Use it for drill holes for board mounting.
Holes diameter 3.5mm.
Do not allow the board to bend, it can break the board.
All ribbon cables are 1M long, enough for placing all connections and you can cut extra length.
Panic button is not included in the kit. In case of panic - enough turn off and turn on the synth.
This picture shown first (1) pin/wire on all connectors:
All next wire should be connected to each key contact or to the main board:
The next picture shows the pinout for 8 wire ribbon cable and pin number of wires:
Same you can see on bottom side of PCB for more convenience.
You will need to connect wire 4 (GND) with LED and button. All other wires in this kit required only one point of soldering.
(7) V+ and (8) GND can be soldered to one of SM304A ICs. (Wire 7) to pin 19. (Wire 8) to pin 1. Or at power supply to +12V.
All next wire should be connected to each key contact or to the main board:
Board pinout and MIDI note:
All note wires can be connected to every note key contact or directly to SM304A ICs (use CX-3 schematic to references and table below). Common bus wire should be soldered to ground or common bus for key contacts.
At this point your brain can blow. Let me explain:
Find key contacts for note (B) on the first octave and solder wires from the YELLOW connector. Starting from wire 1. When you finish it, your last wire will be 12 and note (C) on this octave. Your move will go from right to left.
On octave 5 RED, you should start from wire 1 (B). Wire 13 should be soldered to key contacts common bus. Wire 14 (C) should be soldered to last note C.
Pinout reference for SM304A. ZOOM 
One small important thing - use hot glue to fix inserted connectors to protect from disconnecting them during vibration when you ride on tour. Also fix wires strong. Do not leave them holding only on soldering joints.
Process for set MIDI channel:
Stop all MIDI traffic.
To teach with which MIDI channel synth will work - push the black button (LEARN) LED will blink two times and stay ON to wait for MIDI messages on OMNY channel.
Send any note on the MIDI channel which you want for this synth.
When the synth receives MIDI messages, LED will blink five times and turn OFF. And then will ON with every NOTE ON messages on the selected channel.
Now the channel saved to memory and will never change before you push LEARN button again and starts settings process again.