Precision Zone Specializes in Repairs for Okuma VAC-III AC Spindle Drives

The VAC-III is one of Okuma’s most popular conventional spindle drive units. With 3 powerful models, the VAC-III comes in a 6kW, 11kW and 22kW capacity. The VAC-III boasts quick, clean control signal communication through its fiber optic connection to the NC. This fiber optic connection allows for faster transmission of data and immunity from electromagnetic interference on the signals. Standard copper cables are used for encoder, resolver and winding select connections. Easy access fuse holders on the edge of the power board allow for the ability to quickly check for and replace blown fuses. With distinct, bright LEDs on the control board, the VAC-III provides easy to read LED indication for alarms and operation status.

A pair of large seven segment LEDs gives the user clear alarm and operation status read out in conjunction with the standard LED indicators. This alarm data is also transferred to the NC which displays the alarm name and alarm data on the main screen.

When assessing the functionality of an Okuma Spindle Drive, our 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 mega ohm 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.

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 VAC-III Spindles

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. 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, printed circuit boards 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

Precision Zone repair technicians use digital multimeters with diode testing capabilities and also take resistance measurements to conduct a static test. For these units in particular, our team of technicians uses the diode function of the multimeter as well as huntron devices to check the output modules.

Positive Lead Negative Lead Reading
U Positive Bus Terminal 0.34V-0.40V
V Positive Bus Terminal 0.34V-0.40V
W Positive Bus Terminal 0.34V-0.40V
Negative Bus Terminal U 0.34V-0.40V
Negative Bus Terminal V 0.34V-0.40V
Negative Bus Terminal W 0.34V-0.40V

The capacitor values on the PCBs are verified and any relays, contactors or circuit breakers in the drive are examined to ensure proper functionality.

Checks Under Power and Alarm Code Verification

Upon successfully passing all visual and static checks, the drive is tested under power. Any reported alarm codes are verified and if no alarms are present or once the drive has been fully repaired, the drive is tested in our Okuma simulator. Alarms and drive status can be verified on the LEDs directly on the spindle unit.

On the VAC-III unit, there are a handful of LEDs to display alarm status. The cover of the drive gives the explanations for the various status LEDs. There is a CPUALM LED that indicates an alarm. More specific information can be found from the seven-segment display LEDs along with the adjacent operation status LEDs. The M1, M2 and M3 LEDs are important to monitor as well. These three LEDs indicate faulty operation and should all be OFF for normal running operation.

Common Alarms for the Okuma VAC-III AC Spindle Drive Series

Alarm Code Description Quick Checks
1 Pulse Generator Count
  • Check the output signals of the encoder, that they are present and correct (using Oscilloscop)
  • Check the magnetic encoder sensor or gear
5 DIFF Overflow
  • Check cutting conditions
  • Check for mechanical troubles (no bindings, no problems with lubricating oil systems, etc)
8 Communication Error
  • Check to make sure connectors of optical fiber cables are inserted properly to control board
  • Inspect the fiver optic cable for any breaks
10 Motor Cable Overcurrent
  • Check to make sure terminal screws are tightly secured
  • Check motor and motor cables for short circuits. Use megger to obtain winding resistance values
  • Verify settings at DIP switches SW3 and SW4 are correct
12 Regenerative Transistor Short
  • Check the power supply. An instantaneous power failure may have occurred
  • Check the fuse and IGBT on the control board
19 Motor Overload
  • Check that all the connectors at drive and motor are inserted properly
  • Check the motor cables for short circuits
  • Check resistance of the thermostat relay terminals. The resistance should not be infinite
23 or 37 PG Feedback Fault
  • This alarm is generated when there is no pulse generator signal output or read by the drive
  • Verify connector CN13 is inserted properly
  • Check encoder cables and connectors
  • Check pulse Generator feedback using an oscilloscope

Precision Zone's number one goal is to get you and your business back up and running as soon as possible. To acheive this goal, not only do we offer repair services for your machines, but we also offer free technical support. For more information on these alarms on the Okuma VAC-III Spindle Drive Series and all other machine related issues, please contact us for additional assistance via phone at 800-551-4420 or email at

Discover the Precision Zone Advantage + Repair Benefits to repairing your Okuma VAC-III AC Spindle Drive 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 VAC-III D22 image VAC-III D22 is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: Bad Capacitor(s), Bad Circuit Board Component(s), Bad Control Section/Board, Bad Cooling Fans, Bad Gate Section/Board, Bad Magnetic Contactor, Relay, Bad Output Transistors/SCRs
Drive Type: VAC-III AC Spindle Drive
Rated Capacity: 22kW

Okuma VAC-III D6 image VAC-III D6 is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: Bad Capacitor(s), Bad Circuit Board Component(s), Bad Control Section/Board, Bad DC Bus Capacitors, Bad Gate Section/Board, Bad Magnetic Contactor, Relay
Drive Type: VAC-III AC Spindle Drive
Rated Capacity: 6kW

Okuma VAC-III D11 image VAC-III D11 is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: May Require Board Replacement, Bad Circuit Board Component(s), Bad Gate Section/Board, Bad Input Diodes/SCRs, Bad Output Transistors/SCRs, Bad Power Board
Drive Type: VAC-III AC Spindle Drive
Rated Capacity: 11kW