Yaskawa VS-626M5 machine tool spindle is the most innovative  spindle drive available from Yaskawa. The spindle drive consists of two components, the VS-626M5 inverter (M5) and the VS-626MR5 converter (MR5). The MR5 rectifies incoming AC voltage into DC voltage, while the M5 inverter outputs the simulated AC signal sent to the motor by means of pulse width modulation (PWM).

The DC bus bars connect the inverter and converter units that supply DC voltage to the inverter. 
Advantages of the M5 spindle are that they are high reliable, have high speed capabilities, and provide precise speed, torque, and current control; this enables the spindle to hold tight speed and torque tolerances. The converter regenerates all excess power directly to the incoming line, allowing for superior deceleration times as compared to regeneration via resistors. Quicker spindle deceleration yields faster tool changes, which results in increased machine productivity. All of these advanced features lead to a great product and design.
Common Failures - Causes and Troubleshooting Steps:
Most common causes of AL-01 overcurrents are:
1) Weak insulation on spindle motor/cables.
A megger is required to properly test insulation resistance. See our video here for additional help and tips related to megging a motor. Keep in mind that motor insulation usually decreases as it warms up. Ideally, the motor/cable is megged as soon as possible after the failure in order to get the most accurate megger readings possible
2) The M5 inverter has an issue with the outputs inside the drive. 
 This is another common failure that can be caused by weak insulation of the motor/cables, or can occur due to a parts failure within the drive.The best way to determine if your inverter has suffered a parts failure is to:
a) Disconnect motor leads U, V, and W, and then power on the machine. If the inverter still has AL-01, the outputs have been damaged. It is recommended to send your inverter and converter in for repair and get the motor inspected.
b) Using a multimeter, perform a static check similar to the procedure shown in our video here