Mistubishi HF-KP AC Servo Motor Repair Experts

Here at Precision Zone, we specialize in Mitsubishi product repairs, servicing a wide range of AC servo motors. One series that we work on quite often is the Mitsubishi HF-KP series AC servo motor.

The HF-KP series of AC motor from Mitsubishi is an ultra low inertia and small capacity series. This series is primarily used with an MR-J3 series servo amp. There are a few different options that can be chosen from when using this series of motor. The rated outputs are relatively low, ranging from 50W and only going up to 750W. The rated speed is standardized to 3000 rpm and there are options for an electromagnetic brake. Reduction gears are available as well for certain applications and will be denoted in the motor model by: G1 – general industrial machine reduction gear, G5 – flange-mounting flange output type for precision application, or G7 – flange-mounting shaft output type for precision application.

There are three shaft options available with this series, though some are not available at certain output ratings. A standard shaft is applicable on all models, from 50W up to the 750W option, a keyway shaft is available from the 200W unit through the 750W unit, and then a D-cut shaft is available on the 50W model through the 100W model.

When assessing the functionality of a motor, our engineering team typically conducts a six step check:

    1. Visual Overview
    2. Static Test
    3. Back EMF
    4. Feedback Check
    5. Alarm Code Troubeshooting
    6. Disassembly and Cleaning

This overview is Precision Zone’s basic troubleshooting process. Once our repair team starts on the job we use specialized, customized test fixtures, SKF Baker AVAIV-4, Huntron devices, signal generators, oscilloscopes, milli and mega ohm meters, and other necessary tools to assure quality repair.

Most importantly, every repair is fully tested in custom-built simulators under load to replicate real-life working conditions.

Repair Evaluation Process for Mitsubishi HF-KP Series AC Servo Motors

Visual Overview

When conducting a visual check, the technician inspects the motor for any mechanical damage to the power connecter, junction box, rotor shaft, oil seals and encoder covers. During the visual inspection the technician notes excessive dirt, oil or grease on cooling fans and all other parts of the motor.

Static Check Basic

Precision Zone repair technicians use an SKF Baker Advanced Winding Analyzer to fully evaluate the stator winding. The SKF Baker performs a wide range of electrical tests, including surge, DC hi-pot, mega-ohm, and winding resistance tests. In the instance of winding resistance each phase is tested with each other; and the mega ohm readings should be no less than 200 mega ohms.

Winding Resistance Testing

Positive Lead Negative Lead Approximate Reading
U V 0.2 Ω – 10 Ω ¹
V W 0.2 Ω – 10 Ω ¹
W U 0.2 Ω – 10 Ω ¹

¹Reading should be balanced, 10% difference maximum, between all three phase combinations

Mega Ohm Testing

Positive Lead Negative Lead Approximate Reading
U Ground/Unpainted stator area Well above 200 MΩ ²
V Ground/Unpainted stator area Well above 200 MΩ ²
W Ground/Unpainted stator area Well above 200 MΩ ²

² Our recommended minimum is 200 MΩ. Anything close to that 200 MΩ reading can still cause issues as the motor heats up and that value begins to drop lower.

Back EMF Check

If a servo motor passes the static checks it will be back driven and have the back EMF checked. With our in house magnetizing service we can bring back to life most servo motors with weak magnets.

Feedback Check

Repair technicians can test encoders in a number of different ways. Our Mitchell Electrics TI-5000EX system can be used to read, write and record encoder count and data information. We have Mitchell Electrics TI-5250 systems that can be used to see live encoder pulses on an oscilloscope. Connecting encoders directly to the manufacture’s drive is another way we can verify if an encoder is working correctly.

Disassembly and Cleaning

All motors are fully dissembled, washed, and baked. Rotors are checked for bent shafts and bearing journal common problems. The stator winding is rechecked after the baking process. Holding brakes are refurbished and the holding torque is checked. Both the drive end and opposite drive end housing bearing surfaces are checked. Once the evaluation is completed a computer report is generated with all the findings.

Common Failures and Troubleshooting with Mitsubishi AC Servo Motors

Failure Type Common Cause Troubleshooting
Overcurrent Poor motor or cable insulation, phase to phase short, phase to ground short
  • Perform mega ohm test, first through cables then at motor terminals(if applicable)
  • Perform winding resistance test
  • Contact Precision Zone for further information
Feedback Related Alarms Feedback unit failure, issue with feedback cabling, control board failure on drive side
  • Check encoder waveforms if oscilloscope and back-driving of motor is available
  • Connect motor with a different drive if applicable
  • Contact Precision Zone for further information
Motor shaft is locked up Demagnetization occurred, brake malfunction (where applicable), drive side fault
  • Disconnect motor from drive and attempt to spin by hand, if no brake is used
  • If brake is used, verify that it is disengaging appropriately
  • Contact Precision Zone for further information

This list of checks for certain alarms is primarily a good starting point and if any further troubleshooting or technical support is needed feel free to contact us via phone or email to get in touch with our experienced tech support team.

Precision Zone offers free technical support on any component that you may be having issues with. We understand that when your machine goes down, your business stops. That is why our number one goal is to provide you with the best service possible so that you can get back up and running immediately. For any further product information or troubleshooting assistance is needed, please contact us via phone at 800-551-4420 or email us.

Precision Zone Repair Benefits for Mitsubishi HF-KP AC Servo Motors

  • Free quotes and evaluations by our expert technicians include:
  • 12-Month Warranty on Our Parts and Labor
  • Decades of Industry Experience
  • Exchange Options
  • Rush Service Options

Contact Us To Start Your Repair Today!


Recently Repaired Products

Mitsubishi HF-KP13 image HF-KP13 is an
Motors-AC Servo manufactured by Mitsubishi
Discovered issues: Bad DE Bearing, Bad Encoder, Bad Encoder Cover, Bad ODE Bearing, Recommend Refurbishing/Reconditioning
Servomotor Type: HF-KP Series; low inertia,small capacity
Rated Output: 100W
Rated speed: 3000 rpm; 200V
Electromagnetic brake: none
Shaft end: Standard (Straight shaft)
Options: none

Mitsubishi HF-KP73K image HF-KP73K is an
Motors-AC Servo manufactured by Mitsubishi
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Broken Magnets on Rotor, Recommend Refurbishing/Reconditioning
Servomotor Type: HF-KP Series; low inertia,small capacity
Rated Output: 750W
Rated speed: 3000 rpm; 200V
Electromagnetic brake: none
Shaft end: Key way
Options: none