Precision Zone Expertly Repairs Okuma BLIII-D AC Servo Drives

Here at Precision Zone, one of our specialties is the repair services of Okuma Servo units. One series that we often work on is the BLIII-D series.

The BLIII-D series of servo drives for Okuma is available in two sizes. The 75A option is compatible with 15A, 30A, 50A, and 75A. On top of the 75A unit, there is a 150A unit available. The BLIII-D unit can be used as a replacement for BDU units as well as BL-D units. One very important aspect that is necessary to allow this is the proper setting of switch settings located on the top board of the BLIII-D unit. An explanation of these settings can be found here.

These units are also equipped with monitoring terminals which can be accessed upon removal of the small, square shaped cover found in the center of the unit. This allows, through the use of an oscilloscope, checking of velocity command (M1), torque command (M2), load (M3), phase U current command (M4), phase U current feedback (IU), phase V current feedback (IV), and DC bus voltage (VDC). There are several LED’s which are used for troubleshooting that can be viewed through the cutout portion of the cover on these units. These cover potential problems such as over current, under and over voltage, and CPU malfunctions.

When assessing the functionality of an Okuma AC Servo Drive, our expert repair team conducts a four-step evaluation:

  • 1. Visual Overview
  • 2. Static Test
  • 3. Checks Under Power
  • 4. Alarm Codes Verification

This overview is Precision Zone’s basic troubleshooting process. Once our repair team starts on the job, we use specialized and customized testing fixtures, Huntron trackers, signal generators, oscilloscopes, milli and megaohm meters, as well as any other necessary tools we have available to assure quality repair work. Most importantly, every repair is fully tested in our custom-built simulators under load with a motor to replicate real-life working environment.

Precision Zone goes as far as using heating chambers and overnight dynamic testing, when applicable, to guarantee performance of the repaired product when it arrives back with the customer.

Repair Process for Okuma BLIII-D Servo Drives

Visual Overview

When conducting a visual check, the technician inspects the drive for any mechanical damage to the drive itself and any printed circuit boards (PCB). The technician then proceeds to verify connections are tight and correct inside the drive and there are no loose screws, wires or debris. Additionally, the unit is checked for any burn marks on the components, PCBs or chassis. During the visual inspection, excessive dirt on cooling components is noted as well as the functionality of the heat sink.

Basic Static Check

Output Module Testing

The output modules on these units can be tested by use of a digital multimeter with diode checking capabilities. The following table shows where each lead should be and what the reading should show up as. If any of the readings are very different from the rest, this is a good indication of internal component failures and the unit would require further evaluation and possibly repair. Our technicians are also equipped with huntron devices to further verify their integrity.

Positive Lead Negative Lead Reading
U VH 0.81V-0.85V
V VH 0.81V-0.85V
W VH 0.81V-0.85V
VL U 0.31V-0.37V
VL V 0.31V-0.37V
VL W 0.31V-0.37V

Common Alarms for the Okuma BLIII-D AC Servo Drive Series

Alarm Code Description Quick Checks
An overcurrent is output to the motor
  • Check cables for poor insulation
  • Perform megaohm test on motor
  • Check for ground faults
DC Voltage of the inverter is unusually low
  • Verify incoming power lines (phase to phase & phase to ground)
  • Verify incoming power cables
  • Check status of power supply breaker
CPU on control PC has malfunctioned

Switch settings on control PC board are incorrect

  • Verify that settings all match up properly
  • Replace servo drive unit

For a full list of alarm troubleshooting with this Okuma Servo Drive Series, please see the full manual. Okuma product manual can be found at

Precision Zone is focused on getting your business back up and running. Not only do we offer free technical support from our amazing team of engineers, but we also offer a multitude of resources to assist you with troubleshooting and to help you make the right decision for your business. For more information on these alarms for the Okuma BLIII-D Servo Drive Series and all other machine related issues, please contact us for additional assistance via phone at 800-551-4420 or email at

Discover Repair Benefits to repairing your Servo Drives with Precision Zone

  • Free Quotes and Evaluation by expert technicians
  • We have a thorough evaluation process that utilizes visual, static, and power tests to determine the failure of the product so you get a comprehensive and accurate quote. Everytime.
  • 1-Year Warranty
  • All products are covered by our comprehensive warranty. Warranty terms and conditions are product specific.
  • Competitive Pricing
  • We know that you have many different options to go to for your repairs. However, we pride ourselves in being able to provide you with a more affordable and competitive repair option with out sacrificing the quality of service we provide.
  • Flexible Rush Repair
  • To minimize your equipment downtime, we offer mutliple rush repair options. Standard repair time is typically 1-2 weeks. Rush repair options include 3 day, 2 day, next day, and even same day repairs.

Contact Us To Start Your Repair Today!

Recently Repaired Products

Okuma BLIII-D75A image BLIII-D75A is an
Drives-AC Servo manufactured by Okuma
Discovered issues: Bad Control Section/Board, Bad Cooling Fans, Excessive Dirt/Debris
Drive Type: AC Servo Drive
Power Unit Capacity: 75A, Compatible with 15A, 30A, 50A, and 75A
Type: A