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Servo Motor Repair Blog

AC Servo Motor Magnet Repair

Re-Epoxying Magnets onto an AC Servo Motor Rotor

AC servo motors, unlike induction motors, have magnets on their rotors. Permanent magnets are what give AC servo motors such high torque specs. Magnets are made out of rare earth materials like Alnico or Neodemium which cannot be fastened to metal rotors by welding or soldering. The traditional method most manufacturers use to attach magnets to rotors is epoxy (a kind of super high strength glue). However epoxy isn’t enough. Over time as the rotor turns the centrifugal force of rotational motion can dislodge the magnets and cause them to detach.

To counteract the force of inertia a kind of special tape, known as banding material, is wrapped around the magnets to hold them on. Unfortunately even with good epoxy and banding material, both considerations can break down over time.

Servo Motor Magnets Servo Motor Magnet Repair Mixing Servo Magnet Epoxy Clamped

Servo Motor Magnet Repairs From Servotech

These photos depict best what we do to remedy a rotor that’s magnets have come undone. We peel the old banding material off to get down to the raw magnet and remove the magnets that are loose (the magnets don’t actually fall off because they are magnetic and stick to the rotor).

Using a precision device, known as a gauss meter, we find the magnet polarity and strength, marking pole on the magnet itself and strength readings in a separate table of values. Once we have the magnet data for the whole rotor, we mix up our industrial strength epoxy, and clamp the magnets back onto the rotor. We then let the epoxy rest until it is completely cured. Once cured we undergo the banding process, which uses banding material to make sure the repaired magnets have been properly secured.

The rotor is now ready to be magnetized. Conditions that cause servo motor magnets to become dislodged are typically the same conditions that cause a loss in magnetism: namely heat and shock or impact. We re-magnetize the newly banded rotor in our electron discharge magnetizer, and recheck the values of each magnet in the gauss meter.

Servo Magnet Epoxy RebandingServo Magnet Epoxy Final Product

AC Servo Motor Repair Testing

The final test of the magnet strength cannot be conducted until the servo motor has been reassembled and a proper BEMF reading can be taken.

Servotech tests all repaired motors for quality and performance before they leave the shop, ensuring your motor is returned in “like new” condition.

Signs Your Servo Motor Needs Repairs

8 Signs Your Motor Needs Servo Repairs 

Here are some of the most common servo motor problems that should let you know you need to contact a servo motor repair specialist: 

  1. Worn out bearings and bearing houses 
  2. Fluid contamination and leakage 
  3. Motor brake wear 
  4. Motor winding failure 
  5. Brake coil failures 
  6. Resolver failure 
  7. PCB’s faulty components 
  8. Encoder faults 

Servo Motor Repair Services 

Servotech is a servo motor repair specialist who works with a variety of motors from top manufacturers. We are proud to provide exceptional Fanuc motor repair at our facility. Our intensive evaluation and top notch recondition guarantees you of quality. Moreover, we work closely with Fanuc manufacturers who provide us with original specifications that help us to remove nonspecific dynamic or static parts. We have technical data on Siemens motors from the factory that assist us in making necessary servo repairs. With the specification and our experienced technicians restoring your motor back to running condition remains an achievable goal. No one understands spindle motors better than servo repair specialists. We appreciate that spindle motors complement our services since most of them utilize servo-tech. In addition to repairing your spindle, we tune them to ensure they perform optimally. Not everyone successfully repairs spindles because it requires specialized tools, high-end skills, and high precision devices. 

Additional Servo Motor Repairs 

Other servo motor repairs that we offer include the following: 

  • AC
  • DC Brushed 
  • Brushless
  • Hitachi
  • Kollmorgen
  • Mitsubishi
  • Yaskawa

If you are looking for state of the art servo motor repairs in North America in general, contact Servotech. We provide quality services, customer satisfaction guarantee, and rapid response. 

Why Outsource Servo Motor Repair

Are you experiencing servo motor problems? Servotech can help you with our outstanding servo repair program to meet your servo motor repair needs in practically any industry and without sacrificing quality customer service in the process.

Servotech offers a wide range of premier servo motor repair services for customers and have been a nationwide leader in the industry since we were founded in 2004. We’ve worked hard to earn your trust and develop a solid reputation for delivering superior servo motor repairs, outstanding customer service and prompt attention for all your servo repair needs.

You may have discovered that Servotech is based in Connecticut. However, we serve the servo repair needs of businesses across the nation, with rapid response and quick turnaround times on all our servo motor repairs.

Servo motors repair is almost always preferable to replacement and we understand this important concept and work tirelessly to return your servo repairs quickly, so you can get back in business.

We are confident you’re going to love the level of care you receive and the prompt turnaround when we’re working on your servo motor repair.

At Servotech we bring state of the art technology to the table, employing the latest software, hardware, and techniques to get your servo motor back in business as quickly and painlessly as possible.

Among the other reasons we are confident you’re going to love doing business with us are the following:

  • We conduct OEM quality testing on all our servo repairs.
  • We conduct our servo motor repairs in a clean room environment so you never need to worry about environmental contaminants, like dust, grease, and grime in your motors.
  • We take our jobs seriously qualifying for authorizations as SEM, Baldor, and Yaskawa servo repair centers.

At Servotech, we repair all major servo motor brands, including names you know and trust like:

  • Yaskawa
  • Fanuc
  • Mitsubishi
  • Siemens
  • Hitachi
  • Kollmorgen

Additionally, we service AC spindle motor repairs, DC brushed, and brushless motor repair. Many of our repairs are completed within five days of the receipt of the motor and rush repairs are available for completion within 48 hours in many cases. Try Servotech today for your servo motor repair needs and see what a difference we can make for you.

How to Test a Servo Motor

Testing a servo motor can seem like a complicated, confusing and somewhat overwhelming task. However, with the right tools (ohm meter or megaohm) and the necessary knowledge, the process is a simple and straightforward one to follow. By breaking the servo motor testing process down into achievable steps, testing a servo motor can be quite simple and basic.


Servo Motor Test for a Short with a Megaohm Meter

One of the easiest ways to test and troubleshoot a servo motor is by looking for any short or open circuits that exist within the system by testing all three wires (T1, T2, T3) to the ground wire with a megaohm meter.

  • Place the positive lead onto T1 and the negative lead to ground. Go back and repeat these steps forT2 and T3.
  • Make sure the leads on both ends are not touching anything else, including other leads.
  • Each phase should measure between 600 to 2,000 megaohms.
  • If the resistance reading is 0 or shows a low resistance (20 and under), you likely have a short in your system.

Servo Motor Test for a Short with a Ohm Meter

An ohmmeter is an electrical testing tool that measures electrical resistance. By using this tool you can test for a short in your Servo Motor.

  • Start by disconnecting lines T1, T2 and T3 from the drive.
  • Using your Ohm Meter, begin by testing while the cable is still connected to the servo motor.
  • If the reading on your Ohm Meter is 0, you likely have a short in your servo motor.
  • Next, disconnect the cable and test the servo motor and cable alone.
  • Make sure the leads on both ends are not touching anything else, including other leads.

Servo Motor Test for an Open Circuit or Short Between Phases

One of the easiest ways to test and troubleshoot a servo motor is by looking for any short or open circuits that exist within the system by testing all three wires (T1, T2, T3) to the ground wire with a megaohm meter.

  • Start by testing the connections between T1 to T2, T2 to T3 and then bac to T1 to T3.
  • You can expect to see a range between 0.3 and 2.0 ohms with 0.8 ohms being the avg.
  • If you get a reading of 0 there is a short between the phases.

If you get a reading of infinite or 2000 ohms and above, it is an open short.

How To Prevent Liquid Intrusion Into Your Servo Motor

Oil and Coolant, A Killer of Servomotors

Coolant and Oil in Your Motor

Your machine is down and you pull out a faulty servomotor and send it out for repair. The diagnosis is quick, there is coolant or oil in your motor and it needs to be rebuilt. Your motor had a seal on the shaft, sealed plugs, and gaskets between all of the exposed parts. How did your servo motor fill with oil?

There are a number of common routes liquids can take to get into your motor. You need to know these routes in order to prevent liquid intrusion from happening again.

Keep Coolant and Oil Out

Replace Shaft Seal When the Motor Is Worked on

Routine maintenance? Replace the seal. Changing bearings? Replace the seal. It is common for maintenance personal to reuse old seals versus replacing with new ones due to time constraints, budget, or laziness.

Even Environmentally Sealed Plugs Leak over Time

Replace worn plugs especially if there are loose pins that liquid could get around.

Servo Motor Connectors Need to be Mated

Even sealed connectors need to be mated with matching sealed cable connectors to ensure proper protection. Unsealed cable connectors will allow contaminants into gap between motor and cable connectors. As no seal is perfect, this unnecessary exposure to the plug surface will lessen the time it takes for contaminants to infiltrate the connector.

Stacked Laminations Allow Liquid to Leak through

AC servo motors have a stator that is made up of stacked laminations which will allow liquid to slowly leak through them. Some brands, such as Yaskawa, put a thin metal case around the stator to prevent liquid intrusion. Many other manufacturers such as Fanuc do not and just paint over the laminations. We have found that sealing the laminations with a two part epoxy paint significantly reduces the chance of contamination through the laminations.

Avoid Direct Spray on Servo by Oil or Coolant

Make sure that your servo is not being directly sprayed by oil or coolant. If it is not possible, there are many custom solutions out there to modify the motor or cabling to limit exposure.

In Summary

These are some general tips on preventing liquid intrusion into your servo motor. If your servo motor is flooded and you need help send it in to us and we will repair your servo and work with you to find a way to prevent flooding in the future.

Servo & Spindle Motor Technical Support

Servo & Spindle Technical Support

servo & spindle motor technical support

Maintenance personnel should be aware of the potential issues that may arise when you have a servo or spindle motor in production. For those in need of technical assistance, we’ve got you covered. Below you’ll find a list of common issues you may across with your servo or spindle motor and some simple solutions to help you resolve them. If you’re in need of immediate assistance, please reach out. You can give us a call at 860-632-0164 or you can email us at

AC Servo Motor Support

We have an entire department dedicated to AC servo motor repairs. Our technicians are very knowledgeable about a variety of manufacturers and they can help you troubleshoot any alarms or issues you may be experiencing. Some common AC servo motor issues that may arise include:

  • Absolute battery alarm
    • Solution: Make sure your machine is powered up before changing all the batteries in the control cabinet.
  • Abnormal high load percentages on any of the axes
    • Solution: Wipe and oil the ways and ball screws before running the machine.
  • Z axis brake holding
    • Solution: First, block the head of the machine to ensure that the head doesn’t drop. If the brake is easily accessible, then it can be cleaned out to remove oil and other contaminates. If there is an internal brake inside the motor, it will need to be removed for rebuilding.

DC Servo Motor Support

Our DC servo motor technicians are equipped with the necessary tools and resources to provide our customers with technical support. If you have a DC servo motor in production, you may experience some of the following issues:

  • High current alarms
    • Solution: Check the armature circuit with a megger to see if it has low resistance to ground.
  • High pitched squealing noise during startup
    • Solution: Try running the motor in both directions several times. The armature may have some corrosion from sitting awhile. Once the commutator is clear of corrosion, the high-pitched squealing should quiet down.
  • Position alarms
    • Solution: The glass wheel on the encoder may need to be cleaned with an alcohol wipe. Remove any oil, film, or debris that has settled.

Spindle Motor Support

Our spindle motor department is qualified to diagnose any issues you may be experiencing with your spindle motor. Our technicians have years of experience and they can provide you with the technical support you need to get up and running. Some issues that may occur include:

  • Noisy spindle bearings
    • Solution: Run the spindle motor at a low rpm to heat up the motor and solidify the grease that is in the bearing cavity.
  • Strong vibrations since the last time you ran your spindle motor
    • Solution: Let the spindle warm up at a low rpm before running parts. Check to make sure the coupling is tight. If the coupling has any kind of rubber spider make sure it isn’t cracked or broken.
  • Higher than normal load reading on your control
    • Solution: Make sure the spindle is free of any binding or unnecessary preload. If you have a belt running the spindle, check to see if the belt has proper belt tension and that it’s free from any cracking or splitting.
  • Orientation error during a tool change
    • Solution: Verify that the sensor is working correctly. Check to see if the proximity switch for the orientation is going on and off. Most proximity switches have little LED lights on them that will light up when activated.

Still Need Assistance?

If you’ve tried these solutions and you still need assistance, don’t hesitate to contact us. You can call us at 860-632-0164 or you can email us at Our technicians are readily available to help you troubleshoot.

Fanuc Servo Motor Repair Part Inventory

Repair Part InventoryFanuc is the largest manufacturer of automated machinery in the world. Yet, a majority of the replacement parts needed to maintain Fanuc motors and machines have 16-20 week delivery times, if they are available at all. Ultimately Fanuc limits what “end users” can and can’t do to their machines. Servotech knows that our customers can’t wait 16 weeks for a part, and can’t have a machine down for 16 weeks. We also know it’s impractical for our customers to stock every part they may need, just in case the motor breaks.

Since Fanuc has limited part availability, Servotech has made it our policy to stock as many Fanuc servo motor components as we can. By inventorying more parts, different parts and higher quantities of all parts we eliminate the 16-week delivery time. From spindle motors fans to sensors, we have a healthy supply of the most commonly used components that are vital to Fanuc servo motor and Fanuc spindle motor repairs.

Even though we stock a large quantity of parts, there is the challenge of obtaining servo motor parts that completely unavailable. We came to a point where we either had to give up or get creative. We chose creative ingenuity. We now stamp our own Fanuc Fanuc Partsgaskets for back caps and conduit box covers. Through the use of additive manufacturing (3-D printing) we can recreate or replace small or easily broken plastic components right in house. In the case of some spindle motors we have even re-designed the motors with hybrid bearings.

It is because of these measures that Servotech is able to offer a reliable, rapid response option for Fanuc servo motor repairs, as well as a multitude of other manufacturers whose parts are un-obtainable. Our parts are as good as, or even better than, the original Fanuc components, and our response time for repairs leads the servo motor industry. Ultimately we work hard every day to keep our shelves stocked with parts, so you can keep making parts.

When To Repair or Replace Your Servomotor

Maintenance & DC Servo Motor Repair – Undercutting

Undercut Your Motors, Not Your Success

Did you know that changing the brushes in your DC servo motor may fix some of your issues and keep you running in a pinch? Did you also know that a brush change is only a temporary fix?