Make sure the rate pot is soldered properly…just re-flow those joints to make sure. Check the voltage on the corresponding microcontroller pin (pin # 25) to ensure voltage is getting there…it should be between 0 and 5 volts depending on how the knob is set. If all that looks good then it may be that your microcontroller fell victim to a static discharge somewhere along the way. This happens sometimes which causes the ADCs on the microcontroller to not function anymore.
-Brach