I am running a Prusa Mendel I2 3d printer through the software and firmware of Repetier Host Mac. I have flashed the Arduino MEGA 2560 with the latest Repetier 0.83 firmware. I have complete control of x and y axis in both + and - directions as well as being able to control the extruder and the hot bed temperature. I can expel filament when the temperature is right for the extruder. My problem is that when I try and send a signal to the z axis, the motors receive a signal from Repetier but all they do is whine. No motor action is observed. I have tested each motor on the y axis and they operate as expected. I have adjusted the POT for the z axis full close to full open while the signal is running and the motors are whining. It definitely changes the response of the motor but even at full open the motors just whine. I don’t know if my configuration settings in the Eeprom are not configured for 2 z axis motors or if my steps/mm are set wrong. I am at the end of where my troubleshooting knowledge can take me. Any help would be greatly appreciated.