Today we are going to discuss the Mitsubishi MR-S11/S12 Servo Drives as well as common failures with these Mitsubishi Servo Drives. Below we list common alarm codes associated with these servo drives from Mitsubishi and a few troubleshooting steps you can take. Remember, it is very important that you maintain proper safety while troubleshooting your CNC Equipment. If you missed our blog on proper CNC troubleshooting safety, check it out {HERE} to learn the do's and don'ts. 

Overview of Series:

Mitsubishi MR-S11/S12 AC servo drives are a direct replacement for the earlier MR-S1/S2 units, respectively. A few of the features that this series offers are an enhanced all-digital control which was used previously in the conventional MR-S series systems, individual CPUs being used to control individual axes, allowing enhanced machining accuracy, and gate array control card components which allows improved reliability by using less cables and parts.

This series of drives offers a pair of seven segment displays to clearly display alarms and allow easy readability for the user, in the case of a unit alarming out. The full list of alarms can be found {HERE}, but one of the most common (alarm 32) will be briefly coved below.

Common Failures – Alarm Codes and Troubleshooting Steps:

One of the most common alarms is alarm 32 which refers to an overcurrent being detected. This can be triggered by issues within the motor, the motor cabling, or component failure within the drive unit itself. Occasionally, a failure stemming from the motor can lead to failed components within the drive so both of the following tests are highly recommended, even if something is found during the first test.

For overcurrent issues, there are a few quick checks which can be done while onsite to help isolate where the failure is being produced from.

  1. Weak insulation within the motor or the motor cables
    1. This is one of the most common causes of overcurrent alarms that we see. To check this onsite, a megger will be required. We offer a quick video on how to check the motor using one which can be found {HERE}, as well as offering a Hioki brand megger for sale. If one needs to be purchased, please contact our sales department at (847)-465-9060 and we would be happy to assist you. A standard multimeter can be used following the megger test to check resistance between each combination of legs from the motor (U-V, V-W, U-W), which should all come up with a relatively low reading and each reading should be the same.
  2. Issues with the output section within the MR-S unit
    1. As previously mentioned, this can sometimes be caused by issues with the motor leading to components in the drive being damaged. One of the first things that can be done to verify the drive integrity is to verify motor leads (U, V and W) are disconnected and attempt to power up the machine again. Based on when the alarm occurs, try to reproduce the issue in the same manner. If the overcurrent alarm persists, the output of the drive itself has been damaged and requires further evaluation/repair.

For any additional technical support, troubleshooting, or inquiries regarding repair/purchasing of MR-S11/S12 drive units, please contact us at (847)-465-9060 and one of our customer service representatives would be happy to assist you. 

At Precision Zone, we guide our clients towards to best decision that serves their business. If you have specific repair or replacement questions, get in touch with our expert customer support team at 800-551-4420 or