what breakout board or controller are you connecting the PWM converter to ???
I have not found the instructions for the board but going by this photo found on the net
the yellow jumper selects one of two resistors to limit the opto-isolators LED current
330 ohms for a 5V PWM input which will be correct for most Mach3 breakout boards sold
or
2700 ohms for a 24V PWM input used by industrial PLC controls for example
with no other controls I can only assume the potentiometer has enough range to adjust the output to either 5V or 10V
with the PWM signal on nearly 100% of the time
seeing the 78M12 12V regulator on the board
I would expect the minimum input voltage should be 14V not 12V as printed on the board -
usually the "78xx" and "79xx" regulator require the input voltage to be a minimum of 2V more than the designed output voltage to work correctly
John
PS
I expect the unused pcb pads to for an ceramic capacitor that has not been fitted