Our Team Expertly Repairs Mitsubishi SJ Series AC Spindle Motors

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

The SJ series of AC spindle motors from Mitsubishi come in a range of different variations. The rated output for this series starts at 3.7kW and can go up to 30kW. The maximum rated speed will vary, depending on the rated output and application of use. This speed will generally be 1150 rpm, 1500 rpm, or 5000 rpm, but there are certain instances of 'special speeds' being available for certain application. This series comes in three distinct variations as well - standard type, high-speed type, and special max speed type. Additionally, an optional z-phase control can be equipped when used in specific applications.

When assessing the functionality of a motor like this Mitsubishi SJ Series of 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 Process for Mitsubishi SJ AC Spindle Motor Series

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 a 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 0.2Ω - 10Ω¹
V W 0.2Ω - 10Ω¹
W U 0.2Ω - 10Ω¹

¹ This reading should be balanced across all three phases

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 at 1000V³ being the test point. Anything close to that 200 MΩ reading can still cause issues as the motor heats up and that value begins to drop lower.

³ Note that the lower the test voltage, the higher the resistance reading should be. Ex: Using a 500V test point, minimum reading value rises to 400 MΩ.

Back EMF Check

If a spindle 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 Spindle Motors

Failure Type Common Cause Troubleshooting
Overcurrent Poor motor or cable insulation, phase to phase, short, phase to ground short
  • Perform mega ohm test to ground, first through cables then at motor terminals (if applicable)
  • Perform winding resistance test (phase to phase resistance)r failures
  • Contact Precision Zone for more 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 more 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 at the appropriate voltage
  • Contact Precision Zone support for further troubleshooting

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 SF-PF AC Spindle Motor Series

  • 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 SJ-22AP image SJ-22AP is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Worn DE Housing, Worn ODE Housing
Drive Type: SJ AC Spindle
Output power: 22kW
Base speed: Standard; 1500 RPM
Special type: P
Options: Standard

Mitsubishi SJ-11XW4M image SJ-11XW4M is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Incorrect Feed Back Alignment
Drive Type: SJ AC Spindle
Output power: 11kW
Base speed: Special speed
Special type: Wide-range constant output type
Options: Equipped with Z-phase control

Mitsubishi SJ-15A image SJ-15A is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Recommend Refurbishing/Reconditioning
Drive Type: SJ AC Spindle
Output power: 15kW
Base speed: Standard; 1500 RPM
Special type: Standard
Options: Standard

Mitsubishi SJ-11AW4M image SJ-11AW4M is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Recommend Refurbishing/Reconditioning, Winding Overheated, Worn DE Housing, Worn ODE Housing, Bad Coil Resistance
Drive Type: SJ AC Spindle
Output power: 11kW
Base speed: Standard; 1500 RPM
Special type: Wide-range constant output type
Options: Equipped with Z-phase control

Mitsubishi SJ-7.5AP image SJ-7.5AP is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Recommend Refurbishing/Reconditioning, Worn DE Housing
Drive Type: SJ AC Spindle
Output power: 7.5kW
Base speed: Standard; 1500 RPM
Special type: P
Options: Standard

Mitsubishi SJ-18.5BW4 image SJ-18.5BW4 is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Bad Coil Insulation, Bad DE Bearing, Bad Encoder, Bad ODE Bearing, Recommend Refurbishing/Reconditioning, Bad Encoder Cover, Bad Fan
Drive Type: SJ AC Spindle
Output power: 18.5kW
Base speed: Semi-standard; 1150 RPM
Special type: Wide-range constant output type
Options: Standard

Mitsubishi SJ-11AP image SJ-11AP is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Bad DE Bearing, Recommend Refurbishing/Reconditioning
Drive Type: SJ AC Spindle
Output power: 11kW
Base speed: Standard; 1500 RPM
Special type: P
Options: Standard

Mitsubishi SJ-11AW5 image SJ-11AW5 is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Recommend Refurbishing/Reconditioning, Bad Fan
Drive Type: SJ AC Spindle
Output power: 11kW
Base speed: Standard; 1500 RPM
Special type: Wide-range constant output type
Options: Standard

Mitsubishi SJ-26BZ image SJ-26BZ is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Bad Coil Insulation, Bad DE Bearing, Bad ODE Bearing, Recommend Refurbishing/Reconditioning
Drive Type: SJ AC Spindle
Output power: 26kW
Base speed: Semi-standard; 1150 RPM
Special type: Special max.speed type
Options: Standard

Mitsubishi SJ-18.5A image SJ-18.5A is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Bad Coil Insulation - Due to Coolant/Moisture Contamination, Bad DE Bearing, Bad ODE Bearing, Recommend Refurbishing/Reconditioning
Drive Type: SJ AC Spindle
Output power: 18.5kW
Base speed: Standard; 1500 RPM
Special type: Standard
Options: Standard

Mitsubishi SJ-26B image SJ-26B is an
Motors-AC Spindle manufactured by Mitsubishi
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Recommend Refurbishing/Reconditioning, Worn DE Housing
Drive Type: SJ AC Spindle
Output power: 26kW
Base speed: Semi-standard; 1150 RPM
Special type: Standard
Options: Standard