Worked on number 22 robot tonight. It alarms while stacking the parts on the belt during the down stroke at random pack numbers. The alarm is displayed as a Y inverter fault and it states the Y speed cannot be controlled. I changed out the y-axis encoder, switched the Y and Z inverter cards, and checked all the connections to the circuit board under the x-axis cover. I checked the different voltages on the main transformer to make sure they were within tolerance and monitored the inverter power supply voltage while the robot was operating and everything seemed ok. I tried changing the y-axis pack speed to different values also.