Excel mill has swing arm that changes tools. When it grabs the tool in the spindle, it hangs for a second and then drops down with the tool and continues the change cycle. Sometimes, after it pulls the tpol and drops down it rotates toward home but quits half way. Have to manually push the relays inside the machine to complete the cycle.

However, It works perfectly with no tool in the spindle. There doesn't seem to be anything wrong mechanically.

The signal to the relay that controls the rotation of the arm drops before the arm completes its cycle. Manually activating the relay completes the cycle.

Any help to fix this problem or where to look to further diagnose will be appreciated.