Our Team Expertly Repairs Okuma BL-MH Series AC Servo Motors

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

The BL-MH series AC servo motors from Okuma come in quite a few different variations. The rated torque starts at 5.7 N-m and can go up to 45.3 N-m. On top of torque rating, different rated speeds are available at 1200 rpm as well as 2000 rpm. This series of motor has two shaft options: straight or tapered. Depending on the application, these motors also offer revisions with or without a brake.

When assessing the functionality of a motor, our repair team conducts a five-step evaluation:

    1. Visual Overview
    2. Static Test
    3. Back EMF
    4. Alarm Code Troubleshooting
    5. 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 Okuma BL-MH AC Servo Motors

Visual Overview Check

WWhen 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
¹ 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. 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 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

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 troubleshooting
Encoder Related Alarms Encoder Failure, issue with feedback cabling, control board failure on drive side
  • Check encoder waveforms if oscilloscope and backdriving of motor is available
  • Connect motor with a different drive of applicable
  • Contact Precision Zone Support 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 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. For more information on these alarms as well as any other failures, please give us a call at 800-551-4420 or email us today!

Precision Zone Repair Benefits for Okuma AC Servo Motors

    1. FREE evaluation by expert technician includes:
    • Visual Inspection
    • Static Check
    • Power Tests
    2. FREE job estimate
    3. 12 month warranty on our parts and labor
    4. Flat Price
    5. Exchange Option
    6. Rush Service


Recently Repaired Products

Okuma BL-MH201E-20SN-A image BL-MH201E-20SN-A is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Bad Condition - Requires Reconditioning
Series: AC servo motor
Torque: 21.8 N-m stall
Control Type: E
Rated Speed: 2000 RPM
Shaft: Straight
Brake: without brake
Option: N-A

Okuma BL-MH301E-20S image BL-MH301E-20S is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Broken Shaft, Bad DE Bearing, Bad ODE Bearing, Broken DE Housing, Bad Condition - Requires Reconditioning
Series: AC servo motor
Torque: 36.3 N-m stall
Control Type: E
Rated Speed: 2000 RPM
Shaft: Straight
Brake: without brake
Option: none

Okuma BL-MH201E-20SB image BL-MH201E-20SB is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Bad Condition - Requires Reconditioning, Worn Brake Needs Reconditioning
Series: AC servo motor
Torque: 21.8 N-m stall
Control Type: E
Rated Speed: 2000 RPM
Shaft: Straight
Brake: with brake
Option: none

Okuma BL-MH101E-20T image BL-MH101E-20T is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Bad Condition - Requires Reconditioning
Series: AC servo motor
Torque: 11.9 N-m stall
Control Type: E
Rated Speed: 2000 RPM
Shaft: Taper
Brake: without brake
Option: none

Okuma BL-MH301E-12S image BL-MH301E-12S is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Bad DE Bearing, Bad Encoder Cover, Bad ODE Bearing, Bad Condition - Requires Reconditioning
Series: AC servo motor
Torque: 36.3 N-m stall
Control Type: E
Rated Speed: 1200 RPM
Shaft: Straight
Brake: without brake
Option: none

Okuma BL-MH401E-12SB image BL-MH401E-12SB is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Bad Condition - Requires Reconditioning
Series: AC servo motor
Torque: 462 Kg-cm stall
Control Type: E
Rated Speed: 1200 RPM
Shaft: Straight
Brake: with brake
Option: none

Okuma BL-MH301E-20SB image BL-MH301E-20SB is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Broken Magnets on Rotor
Series: AC servo motor
Torque: 36.3 N-m stall
Control Type: E
Rated Speed: 2000 RPM
Shaft: Straight
Brake: with brake
Option: none

Okuma BL-MH201E-20S image BL-MH201E-20S is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Bad Condition - Requires Reconditioning
Series: AC servo motor
Torque: 21.8 N-m stall
Control Type: E
Rated Speed: 2000 RPM
Shaft: Straight
Brake: without brake
Option: none

Okuma BL-MH201E-12S image BL-MH201E-12S is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Bad Condition - Requires Reconditioning
Series: AC servo motor
Torque: 21.8 N-m stall
Control Type: E
Rated Speed: 1200 RPM
Shaft: Straight
Brake: without brake
Option: none

Okuma BL-MH201E-12SB image BL-MH201E-12SB is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Bad Condition - Requires Reconditioning
Series: AC servo motor
Torque: 21.8 N-m stall
Control Type: E
Rated Speed: 1200 RPM
Shaft: Straight
Brake: with brake
Option: none

Okuma BL-MH101E-20S image BL-MH101E-20S is an
Motors-AC Servo manufactured by Okuma
Discovered issues: Bad DE Bearing, Bad ODE Bearing, Bad Condition - Requires Reconditioning
Series: AC servo motor
Torque: 11.9 N-m stall
Control Type: E
Rated Speed: 2000 RPM
Shaft: Straight
Brake: without brake
Option: none