Finally made my breakout cable, and got the following results:
Pin Voltages Dir Name Comment
1 0.0v Out ENC_A Encoder A Output
2 0.0v Out ENC_B Encoder B Output
3 0.0v Gnd GND Ground
4 1.6v In CYM Ink Control
5 0.0v / 0.9v / 1.1v ? CYM Ink Control
6 0.0v Gnd GND Ground
7 0.0v / 1.5v ? Disconnect - No effect
8 0.0v / 1.5v ? Disconnect - Immediate stop of printing
9 0.0v Gnd GND Ground
10 1.6v In Black Ink Control
11 1.1v / 0.9v / 0.0v Out Black Ink Control
12 0.0v Gnd GND Ground
13 0.0v Disconnect - print continues, no ink output
14 0.0v Disconnect - immediate stop of print, E - Ink
15 3.3v Vcc VCC 3.3v for logic
16 0.0v ? Disconnect - immediate stop of print, no error
17 16v In VINK Voltage for ink jet
18 16v In VINK Voltage for ink jets
19 16v In VINK Voltage for ink jets
20 16v In VINK Voltage for ink jets
So, interestingly, looks like all the CYM ink control is on just one shift register.
Next, need to set up some LEDs to see if I can figure out which signals are used when, until I can get a good logic analyzer attached.
For now, investigation will focus on pins 4,5 and 10,11.
Hopefully the LED test will reveal which of the other pins is the ink shift register clock.