Our Team Expertly Repairs Okuma VAC-II Spindle Drives

Okuma’s VAC-II drive is the precursor to the popular VAC-III series AC spindle drive. The VAC-II continued the tried and true design of the VAC-I and can still be found in many machines today.

Status LEDs show power, alarms and general drive status. Both standard LEDs along with 7-segment displays illuminate this information to the user. The design of the VAC drives allows for easy maintenance and troubleshooting, as well as quick board replacement when needed. The VAC-II manual contains information for checking various signals on the unit for general preventative maintenance as well as for assessing irregularities with output signals.

Here at Precision Zone, we pride ourselves on being repair experts on Okuma products including this series of Okuma VAC-II AC Spindle Drives.

When assessing the functionality of a drive, our repair team conducts a four-step evaluation:

    1. Visual Overview
    2. Static Test
    3. Checks Under Power
    4. Alarm Code 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 VAC-II Spindles

Visual Overview Check

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

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-0.4V
V Positive Bus Terminal 0.34V-0.4V
W Positive Bus Terminal 0.34V-0.4V
Negative Bus Terminal U 0.34V-0.4V
Negative Bus Terminal V 0.34V-0.4V
Negative Bus Terminal W 0.34V-0.4V

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

Check 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-II 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.

Alarm Code Description Checks
1 Pulse Generator Count Abnormality
  • Check the output signals of the encoder are present and correct (using an oscilloscope)
  • Changing magnetic encoder sensor or gear
5 DIFF Overflow
  • Check cutting conditions
  • Check for mechanical troubles (no bindings, no problems with lubricating oil system, etc.)
8 Communication Error
  • Check to make sure connectors of optical fiber cables are inserted properly to control board
  • Inspect the fiber optic cable for any breaks
10 Motor Cable Overcurrent
  • Check 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 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 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

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 Spindle Drives

    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 VAC-II D30A image VAC-II D30A is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: Bad Capacitor(s), Bad Circuit Board Component(s)
Drive Type: VAC-II AC Spindle Drive
Rated Capacity: 30kW
Design Revision Order: A

Okuma VAC-II D11A image VAC-II D11A is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: Bad Fuse, Bad Gate Section/Board, Bad Output Transistors/SCRs
Drive Type: VAC-II AC Spindle Drive
Rated Capacity: 11kW
Design Revision Order: A

Okuma VAC-II D8A image VAC-II D8A is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: Bad Circuit Board Component(s)
Drive Type: VAC-II AC Spindle Drive
Rated Capacity: 8kW
Design Revision Order: A

Okuma VAC-II D45A image VAC-II D45A is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: Bad Capacitor(s), Bad Control Section/Board, Bad Cooling Fans
Drive Type: VAC-II AC Spindle Drive
Rated Capacity: 45kW
Design Revision Order: A

Okuma VAC-II D22B image VAC-II D22B is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: Bad Capacitor(s), Bad Circuit Board Component(s)
Drive Type: VAC-II AC Spindle Drive
Rated Capacity: 22kW
Design Revision Order: B

Okuma VAC-II D22A image VAC-II D22A is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: Bad Output Transistors/SCRs
Drive Type: VAC-II AC Spindle Drive
Rated Capacity: 22kW
Design Revision Order: A

Okuma VAC-II D11B image VAC-II D11B is an
Drives-AC Spindle manufactured by Okuma
Discovered issues: No Display
Drive Type: VAC-II AC Spindle Drive
Rated Capacity: 11kW
Design Revision Order: B