I can help you.
Do you have User's Manual for such board? If not, i can send by e-mail.
In short words, the initial settings are following:
Rotary switch on board:
The rotary switch (positions 1....9) on that TTL board is purposed for strobe type select. For Inon Z-240 you must set it to "1" position.
But on your photo i see that switch at "0" position, which means fixed M mode set by hardware tools. You have to set it to "1", then TTL will work.
If TTL works normally, it confirms by "green" LED light on the board after each shot. In M mode the LED light is "blue". If battery is low, LED lights "Red'.
Switching TTL/M by Nikon camera menu:
Check your camera menu sync speed setting.
For TTL mode in system you have to set any normal sync speed by your camera menu, for example 1/200 (any speed without "Auto FP" mark). Because "Auto FP" command in that menu is assigned for fast switching electronics to M mode underwater.
Fiber optical cables:
Use only new Nauticam #26216 fiber optical cables (613 cores inside), this TTL board is tuned for them.
Inon Z-240 initial settings:
Set Z-240 left dial (mode selector) to "S-TTL" position.
Set Z-240 right dial to "12 o'clock" position, as initial setting. This means zero correction +/-. Later you can use +/- exp.compensation by that right dial, as well as by camera +/- flash exp. compensation.
Set Z-240 magnet to "down" position (push down and lock).
- TimG likes this