Today, we are going to show you how to troubleshoot your AC Servo Motor. Two of the most common failures that happen with the motors are over-current faults and ground faults. Below, we explain to you the three simple steps to static checking both of these faults. We have also included a video at the end to help see exactly what to do.

Safety First

Use Caution

When it comes to troubleshooting problems on-site, safety is extremely important.
To read more on troubleshooting safety, check out our blog post here.

Visual Checks

Always check the physical status of the unit before performing any other troubleshooting steps.

What to look for:


Static Checks

Before performing any static checks, verify that the DC Bus is discharged using a multimeter. Then you can disconnect the power cable from the drive. By not disconnecting the power cable, you could cause damage to the drive while megging the motor.

There are 3 things we are going to check with our megger:

  1. Motor connected to the power cable
  2. Power cable alone
  3. Motor alone


First, with the power cable attached to the motor, use a megger to check for ground faults between U, V, and W. Any reading of 300 megaohms or more is okay. Next, disconnect the power cable from the motor. Using a megger, check the inputs of the power cable to ensure the issue does not reside within the cable. Lastly, use a megger to check the motor through the pins of the power connector. Remember: A, B, and C pins on the motor are considered to be U, V, and W. Here is a video to help guide you through the process!

At Precision Zone, we guide our clients toward the best decisions that serve their business needs. If you have specific repair or replacement questions, get in touch with our expert customer support team at 800-551-4420 or

Written by:

Marketing & Creative Director at IcarTeam, and supporting afiliated businesses,
including Precision Zone, Precision Education Integrators and Alfra Tools.
Did you like this article? Click your favorite social media channel to share it with your friends and colleagues
You might also enjoy these articles:
Recent articles:


You know who we are, what we do and how we do it, so let's get started!


Get the latest news, tips, insights and product spotlights sent straight to your inbox weekly

By entering your email, you agree to our Terms of Service and Privacy Policy.
Call Us Now!