Interesting, i'll have to get the 'scope out again some time.
Now i think about it, there are some notes in the drive manual about the index pulse being short so they included an open collector output as well - presumably the pulse is longer?
Maybe i need to remove the main index pulse input and use the O/c index pulse instead somehow?
Quote...
5. Encoder Z signal open collector output
Servo drives to open collector mode on the output signal of the encoder Z. Because Z letter feel the pulse width is narrower, PC
please use high-speed photoelectric coupler receiving.