Does the clutch engage? There's a separate solenoid that engages the motor to the controls.. apply power to pins 1 and 2 (power on 1 and ground on 2) and you should hear a click and the stick should get stiff (clutch engaged).. If this doesn't happen, the motor can spin disengaged all day long and it won't move the control surfaces. Motor movement is on pins 3 and 4 (reverse polarity to move the motor in other direction).
To my knowledge they do not use shear pin but it's a slip clutch instead.. but not 100% sure.