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Servo Motor Repair FAQ’s

Oil and Coolant, A Killer of Servomotors2019-10-15T02:17:06+00:00

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.

Fanuc Servo Motor Repair Part Inventory2016-12-21T06:40:46+00:00

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.


Maintenance & DC Servo Motor Repair – Undercutting2016-12-21T06:45:03+00:00

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?

DC Servo Motor Repair - UndercuttingIt stands to reason that as brushes wear out. The carbon they are comprised of turns to dust, which only has one place to end up – inside your servo motor! Changing the brushes is a good maintenance step, but it is also an admission that at least one set of brushes worth of carbon is now caked on the inside of the motor.

Furthermore, as brushes wear down, so does the copper motor commutator. Over time a commutator can develop a ridge or grove where brushes have been riding, causing brushes to wear out more quickly or not make proper contact, which leads to higher current draw.

When brushes wear improperly the excessive carbon can get lodged in between the commutator bars and cause a short circuit. The only way to make a DC motor last indefinitely is to rebuild it.

DC Servo Motor Refurbishment – Done Right by Servotech

At Servotech we remove the motor armature and put it through a process known as “Undercutting.” A small toothed blade is actually used to clean out the grooves in between commutator bars, then the armature is put in the lathe and all of the bars are turned down to one smooth surface. Once the bars are smooth, consistent and clean, the motor can be rebuilt, and the brushes can be set properly so that they will run true, and last.

For more information, read about our DC Motor Repair Process or see our article about DC Servo Motor Brush Wear.

Find Authorized Servo Motor Repair2016-12-21T07:02:01+00:00

Find Authorized Servo Motor Repair

Servo motor repair is a specialized challenging field. Servo repair techniques and procedures are often the result of companies who have researched through trial and experience. Servo motor manufacturers like to model their business after the automotive industry; constantly pushing new products lines, innovating year after year, and encouraging the sales of newer, faster and more precise machines.

A lot of companies out there throw around terms like, “Qualified Servo Motor Repair Center”, or “Official Servo Motor Authority”. It is a strategy in search engine optimization to favor certain words and phrases. There is no harm in turning a phrase, except when it is deliberately misleading.

The questions is: “How can you determine if a repair shop is a legitimate authorized servo motor repair center? Is it possible to confirm affiliation with a servo motor manufacturer?” When it comes to servo repair, the shortest response is usually – no they are not authorized, and they are not affiliated!

3rd Party Servo Motor Repair Shops Are Rare

Most manufacturers of CNC machines, and by association servo motors, are not interested in having third party shops repair their equipment. Companies like Fanuc and Mitsubishi do offer repair but at prices that promote buying new servo motors and machines. Because large manufacturers do not find it cost effective to repair their equipment, they just don’t. Additionally, they have no interest in certifying other companies as authorized servo motor repair facilities.

Authorized Servo Motor Repair Claims

Beware the use of servo motor factory logos on websites. It doesn’t take a lot of effort to copy and paste an image of a logo and incorporate it into a website. This can lead consumers to misconstrue a false connection between the motor manufacturer logo and the servo motor repair company. Never assume that a logo is the equivalent of a factory certification.

Some companies use phrases like “Master Servo Motor Repair Center,” and “Primary Servo Motor Repair Center,” to make an implication that there is some connection between the servo repair shop and the servo motor manufacturers they repair. Using language to mislead a customer into choosing a service on false pretenses is dishonest.

Perspective can be difficult to maintain, especially with a machine down, and the need for quick action.

Truly Authorized Servo Motor Repair

Servo motor repair, like any other industry, has its leaders who thrive on the quality of their honest work. At Servotech is has always been our mission to exceed customer expectations and servo motor manufacturer standards. Many of our servo repair processes result in a servo motor that is better than a brand new one from the manufacturer.

During our years in business, we have earned the distinction of being an actual authorized servo motor repair center for some of the world’s biggest servo motor manufacturers. We maintain factory drives, rigorous procedures and the very best servo motor repair procedures to maintain these certifications. Find our more on our:

Stop Overpaying for an OEM Servo Motor!2016-12-31T06:57:56+00:00

 Stop Overpaying for an OEM Servo Motor!Servo Motor Repair

You May Be Paying Too Much for Your OEM Servo Motor

Are you buying your servo motors from your machine manufacturer? You may be paying way too much money! Have you called the servo motor manufacturer and been told “we cannot sell you this motor, call your OEM”? Before you give up hope, there is a strong possibility you can obtain a replacement motor for much less!

How to Configure an OEM Servo Motor Replacement

  • Find the OEM servo motor part number breakdown (frequently found on series datasheet).
  • Find your servo motor part number.
  • Break down your part number to see what’s been changed from the base model.
    • If the change corresponds to a seal, connector, etc. Order the base model servo motor and buy the seal or connector separately.
    • If it’s something else or if you can’t find the change, call 1-888-80SERVO.

Details on OEM Servo Motors

Most OEM servo motors have had modifications made to them specific to their application. These modifications can range from something as simple as connector pin assignments, to something as involved as installing special feedback in the servo. In order to determine the modifications made to the motor there are a few pieces of information you need.

Try to obtain a datasheet or brochure that matches your specific servo motor series from the motor manufacturer. This will very often give you a description of how to break down the servo motor part number – showing how the part number identifies specific properties of your servo. Now you will need the part number off of your motor. Break down your part number using the same format, and see what is different. You will usually find a letter or number in your part number that is not listed as an option in the datasheet – this will correspond with what is different about your servo.

If the change in the part number corresponds to something like a connector or seal that is the most simple option. You can order a servo motor with the closest matching part number and buy the seal or connector separately, directly from the servo manufacturer. Remove the stock seal, connector, etc. and install the unique one – and you just saved a lot of money!

Sometimes the part number will have extra characters at the end, or unique sections that will correspond to something complicated – such as motor torque or shaft dimensions. Look through the manufacturer datasheet and compare all of you servo motor’s physical and electrical specifications to the stock servo, and you should find the modification.

Hopefully you find what makes your OEM servo motor unique, and you can eliminate the high costs and long lead times, and simply buy your servo motor straight from the manufacturer.

If you need assistance in locating a direct replacement for your OEM servo motor, our technicians are here to help! If a replacement does not exist we are your best source for refurbishing your servo motors to new condition – so you can avoid overpaying for an OEM servo motor!

Contact us for more information on buying a servo motor or for servo motor repairs.

Servo Motor Resolver Wiring: Colors & Functions2016-12-21T13:49:21+00:00

Servo Motor Resolver Wiring: Colors & Functions

If you ever plan to replace or test a resolver then you need to know the functions of each wire. This can be very difficult to determine with out a little knowledge and a voltmeter.

There is an industry standard for resolver wire colors that most manufacturers choose to use. These colors are as follows:

Resolver Wire Colors
Wire ColorRed/WhiteBlack/WhiteRedBlackYellowBlue
Wire FunctionExcitation +Excitation –Cos +Cos –Sin +Sin –


Proprietary Wire Colors

Sometimes Yellow/White can be used in the place of Black/White for Excitation. These are industry standard wire colors but you will come across other brands of resolvers with their own proprietary color designations. When this happens you will need to use a voltmeter to assist you in determining wire color versus function.

Determining Circuits

Almost all resolvers have 6 leads. Use a voltmeter to ring out the leads and determine which 3 pairs of wire are circuits. Then record the resistance of each circuit. The Cos and Sin circuit will have the same resistance, so the circuit with the different resistance will be your excitation circuit. If any circuits ring open, or all three circuits have different resistances then your resolver could have a damaged winding and need to be replaced/rebuilt.

These are some basic tips on how to determine a resolvers wiring. In order to continue on and designate exact wire functions on nonstandard wire colors you will need to excite the windings with the proper frequency and use an oscilloscope.

Further Questions

How Can I Excite the Windings?

Before you can determine exact functions of your resolver wires you will need background information concerning the type of output your motor drive or controller is looking for. Most manuals will describe the specific sin and cos outputs used based on the direction rotation. You need this information to proceed.

In order to test your resolver you will need to excite your resolver with the proper voltage and frequency which is typically written on the resolver label. Most resolvers are between 4-6V at 3-10KHz. People who don’t have test equipment that can feed high frequency hook their resolvers to their drive and check the sin and cos outputs either on the drives test points or directly off of the resolver.

Once you have the resolver running on the scope you just need to set up the outputs of the resolver to match the drive/controllers specifications paying attention to the direction of rotation.

Here are some links with some more information on resolver windings:

Does the Mechanical Position of a Resolver Matter When Fitting to a Servo Motor?

The angular position of the resolver stator to the resolver rotor is critical. Most resolver stators are mounted in a way that they can be rotated 360 degrees easily in relation to the motor housing with no alignment pin or key. When the resolver stator or rotor is rotated independent of the other, however, the electrical angle of the resolver relative to the servo motor will change and you will lose your proper alignment.

You can rotate the entire resolver as a unit to any physical position relative to the motor. Many resolver manufacturers mark a line from the rotor to the stator to designate 0 degrees. As long as the lines line up you can put the resolver in any position you like and know your resolver is at 0 electrical degrees.

How Can I Determine Rotor to Resolver Position for Correct Commutation Signals to the Servo Drive?

Your best bet is to find documentation on the drive. There is no way to determine the correct alignment with just the motor. The alignment is whatever the drive needs it to be, which varies drive to drive.

Another way to determine the correct alignment is by examining a sister motor. You will need to use your controller or other equipment to determine the angle of the resolver as there is no zero degree mark.

Servo Motor Connectors: Where Can I Find Them?2016-12-21T13:51:40+00:00

Servo Motor Connectors: Where Can I Find Them?

Your servo motor needs a new connector. The connector is cracked and the pins are all bent. You look at it and think, “Where am I ever going to find this plug?” And even if you find the plug and get it on time, can it be changed easily? Connectors can quickly become a headache. With so many styles, manufacturers, and specific needs there are millions of plugs in production to choose from. Finding your connector can be extremely difficult if you do not know how to search.

Once You Have Found Your Servo Motor Connector…

  • Do you have the tooling you need to install it correctly?
  • Do you have the information recorded when you disconnect the old servo motor connector to connect the new one?

Refine the Search

The first step to finding your servo motor connector is refining your search. This will limit the number if connectors to search through by specific characteristics. Many online companies that sell connectors will let you limit your search by choosing variables such as rated current, shape, number of pins, etc.

If you know the manufacturer of you your servo motor connector (give it a good look over) then you can limit your search or go straight to that manufacturers online site.

If you can obtain a manufacturers part number, many online sites will cross it to their own part number. If at all possible, get a datasheet and verify dimensions before purchasing, you don’t want a close match, you want an exact match.

Collect the Tools You Need

There are some tools that are necessary to install connectors on your servo motor. You will need a soldering iron to solder the pins and sockets. Even if they are crimp pins, many people will solder the crimp to strengthen the joint and prevent fraying.

If the pins need to be crimped invest in a crimper for that style connector. Many connectors are threaded together and you will need wrenches and pliers.

Document Servo Motor Connector Wiring

Always document the servo motor connector wiring before removing the old one. Write down wire colors relative to pin numbers. If possible also document wire functions to pin number as colors are not always easy to differentiate.

Most people forget to document the orientation of the connector in relation to the motor, and also the orientation of the connector hub to the housing of the connector. If these are not correct you may not realize it until you motor is reinstalled into your machine and now the cable does not reach or mate with your motor.

In Summary

These are some considerations to make when changing your connectors on your servo motor. There are many good places to shop for servo motor connectors, and prices can fluctuate greatly, so shop around. If you are having someone else change your connectors make sure they are replacing you old connector with a proper match. Many repair facilities will use unsealed or lower quality replacement servo motor connectors resulting in more problems down the road for you.

Servotech has technicians who spend their day dealing with servo motor connectors, plugs, and manufacturing cables. If you do not have the time or desire to find your connector or build your own cable, we will gladly do it for you!

Contact us for servo motor repair.

How do I disassemble/rebuild my DC servo motor?2018-09-22T12:59:57+00:00

So you think you’ve got what it takes to rebuild your broken DC servo motor. Just a rotor with a couple bearings right? Wrong. There are many factors to consider before disassembling your own DC servo motor.

Substandard insulation, exposed copperElectricity will go to ground
Scratched insulationCorrosion of affection area
Improper winding configurationCommutator worn out, repair or replacement necessary
Nicked or damaged wires in windingsMalfunctioning or burned up motor
Armature removed from wrong type of field frameLoss of magnet strength, demagnetization, servo failure
Damage to tachometer armatures or windingsReplacements necessary
Poor field frame positioning relative to brush riggingTorque loss, over current, motor failure

You Must Be Able to:

Test the Armature Insulation Correctly

There are special testers used to test the insulation that protects the winding from grounding out to the iron on the armature. It is very important that the insulation be up to standard. When the motor is being run under load there is potential for electricity to go to ground.

If there is any exposed copper on the winding this would be a high potential for grounding out during operation. Any area were the insulation is scratched will have a high potential to corrode over time and fail.

Test the Armature Circuit Correctly

There is also special testing equipment to test each circuit of the armature insuring that the windings are going to work to specification. Special attention needs to be paid to the commutator. If the commutator is worn or burned it will need to be turned in a lathe or replaced.

Avoid Damage to the Electrical Windings as You Separate the Armature from the Field Frame

Removing the armature is a delicate process, which is compounded by the magnetic force of the field frame. The exposed wires, and commutator are extremely prone to getting nicked or damaged during the disassembly process. Even minor physical damage to the circuit of the armature can cause a motor to malfunction and burn up.

Separate the Armature from Its Magnetic Field without Causing Demagnetization

There are many types of magnets. The most popular types used in servo motors are Neodymium Iron Boron (NdFeB or NIB), Samarium Cobalt (SmCo), Alnico, Ceramic, Ferrite and Rare Earth. Certain magnet types require that their fields not be broken. If a motor or tachometer armature is removed from the wrong type of field frame, the magnets will loose their strength effectively ruining the servo. The only way to rectify demagnetized field frames on a disassembled servo motor is to recharge the magnets. Otherwise the servo will never run properly.

Avoid Damage to the Tachometer Armature as you Remove It from the Motor Armature

Often, as you try to take the Tachometer off of the motor shaft it can be very hard to remove because of corrosion and tight tolerances. We have made several special removal tools to take the tachometer armatures off to prevent destroying them. The windings on a tachometer armature are smaller than the hairs on your head, and much less resilient to forces applied to them.

Assemble the Field Frame on the Brush Rigging Correctly

The relative position of the field frame to the brush rigging needs to be correct. If this relationship is not correct the motor will not commutate correctly resulting in torque loss, over current, and motor failure.

In Summary

These are a few of the important things to know before you start to take apart your own DC servo motor. If you decided that you want your motor professionally repaired then send it to Servotech Inc. We have all the necessary knowledge and equipment to rebuild you DC servo motor.

How do I disassemble/rebuild my DC servo motor?