Hi Ian,
to MY knowledge, the exact value of the potentiometer (poti) inside an Expression Pedal is NOT that important. The poti works as an electrical "voltage divider" here. So the keyboard only evaluates the voltage RATIO, depending on the current position of the poti. You will always have the full control range (0 - 100%).
It should therefore work properly with resistance values over a wide range (from appox. 10 kOhm up to 100 kOhm).
@tomek27
Please ONLY connect / disconnect Pedals when the keyboard is switched OFF.
During the boot process the keyboard will check the connected Pedals and it tries to automatically set the right Polarity. Important: Do NOT press / turn any of the Pedals until the Main Screen appears.
To change the Pedal settings press Direct Access button and then shortly press / turn the desired Pedal.
If the Pedal should work "reversed", change the Polarity. If your Expression Pedal does still not work properly, it is not compatible with Yamaha keyboards.
In this case, a technician can change the WIRING of the TRS plug. There are THREE different wirings possible, but only TWO of them can be used with Yamaha keyboards.
Best regards,
Chris