WACOGIKEN GPAr-24NTS Servo Driver
NABCO (Nabtesco Corporation / Nabco Marine Systems)
New product
The WACOGIKEN GPAr-24NTS AC Hi Servo is a servo drive / servo amplifier used in marine main-engine electronic governor applications, most notably in documented Nabtesco MG-800 Governor Systems.
Marine spare-parts references specifically identify the GPAR-24NTS as a servo drive unit for the Nabtesco MG-800 marine main-engine governor.
The photographed SM MARINE SERVICE™ stock unit is marked:
Manufacturer: WACOGIKEN
Series: AC Hi Servo
Model: GPAr-24NTS
Product Type: AC Servo Driver / Servo Amplifier
Marine Application: Main Engine Electronic Governor
Documented System Association: Nabtesco MG-800 Governor System
The front of the unit provides clearly labelled:
CN1 – I/O
CN2 – SEN.
CN3 – COM.
VR1 / VR2
TP1 / TP2 / GND
RDY / AO
SPV / A1
Motor terminals U / V / W
together with mains/control-power and braking-resistor connections.
The GPAr-24NTS is an electronic servo driver.
Its job is to take a command from the governor/control system and precisely control the connected AC servo motor or governor actuator.
In a marine main-engine governor system, that means the servo driver forms the power-control link between:
Governor Control Unit → Servo Drive → Actuator → Fuel Regulating Mechanism
The drive itself does not independently determine desired engine RPM. Instead, it follows the governor command and supplies the controlled electrical output required by the actuator.
The strongest documented marine application for this exact model is the Nabtesco MG-800 Digital Governor System. A current marine-market listing identifies GPAr-24NTS specifically as the servo-drive unit for the MG-800 governor.
Nabtesco’s official MG-800 product documentation describes the MG-800 as a digital electronic governor with:
Variable Starting Modes
Overspeed Prevention
Automatic PID Selection
High Gain Mode
Fuel Limiting
Automatic Shutdown
Automatic Slowdown
Touch-panel monitoring
and separates the system into a:
Control Unit
Actuator Drive Unit
Actuator
Pulse Generator.
The GPAr-24NTS is therefore best described for SEO as a:
MG-800 Servo Drive Unit / Governor Actuator Servo Driver
rather than simply a generic industrial servo drive.
A marine electronic governor continuously compares actual engine speed with the required speed command.
The control unit calculates the required correction and sends a command toward the actuator drive.
The servo drive then converts that low-power command into controlled motor power, allowing the actuator to reposition the engine fuel regulating linkage.
The result is precise control of:
engine RPM
acceleration
load response
speed stability
fuel-rack position
within the overall governor system.
A technical description of the MG-800 notes that its actuator arrangement uses an electromechanical servo drive connected to the engine’s fuel-rack mechanism.
A documented MG-800 installation on a Wärtsilä/Sulzer engine identifies the main governor components as:
MCG-402 – Control Unit
ADU-120A – Actuator Drive Unit
EAR-120 – Actuator
with the electronic governor controlling fuel-injection-pump regulating linkage according to engine-speed demand.
Other MG-800 system documentation includes actuator families such as:
EAR-20
EAR-120
EAR-500A
EAR-1000A.
These are valuable related search keywords for ships operating Nabtesco governor installations.
Marine buyers sometimes describe the GPAr-24NTS as:
Actuator Drive Unit
Actuator Servo Driver
Governor Drive Amplifier
AC Servo Amplifier
Servo Control Unit
This terminology occurs because the GPAr sits inside the actuator-control chain.
However, the exact Nabtesco system may have a separate designated ADU assembly around or alongside the servo-driver hardware.
For correct replacement sourcing, the servo-driver model and the overall MG-800/ADU configuration should both be checked.
WACOGIKEN is a Japanese servo-system manufacturer specialising in motor, power-electronics and control technologies. Its current product range includes AC servo drivers and motors.
WACOGIKEN documentation for its later GPX2 servo-driver family explicitly refers to earlier:
GPA
GPP
GPAR
GPPR
families in replacement documentation.
This confirms that GPAr belongs to WACOGIKEN’s established servo-driver lineage.
WACOGIKEN’s GPX2 replacement guide lists old GPAR series alongside other earlier GP servo products.
Current GPX2 servo drivers are available across ratings such as:
GPX2-8
GPX2-12
GPX2-16
GPX2-24
GPX2-40
GPX2-60
GPX2-80.
However, this does not mean that a standard GPX2-24 can be installed directly in place of a marine GPAr-24NTS.
The NTS suffix, control I/O, sensor feedback, parameter settings, MG-800 system integration and connector arrangement must all be verified before any migration.
A very important related model is:
WACOGIKEN GPAR-40NTS
Marine-market references document GPAR-40NTS as another servo-drive unit used with a Nabtesco MG-800 Main Engine Governor.
Therefore strong related searches include:
GPAR-24NTS MG-800
and
GPAR-40NTS MG-800
However, 24NTS and 40NTS must not be considered interchangeable without checking motor rating, drive configuration and system documentation.
The photographed front panel identifies:
CN1 I/O
This is the main control input/output interface.
Depending on the system design, control signals may include:
servo enable
command signals
ready output
alarm output
status/control I/O
The exact pin allocation for this NTS version should be taken from the relevant Nabtesco/WACOGIKEN wiring diagram.
The second connector is marked:
CN2 SEN.
This is associated with servo/motor feedback sensing.
Closed-loop servo control depends on feedback information so that the drive knows the motor/actuator position or operating state.
A fault in the feedback circuit can therefore produce:
loss of actuator movement
unstable movement
alarm condition
incorrect governor response
even if the power section of the drive itself is healthy.
The smaller circular connector is marked:
CN3 COM.
This indicates a communication/service interface.
It may be used for setup, commissioning or system-specific communication depending on the marine configuration.
The exact function should follow the GPAr-24NTS/MG-800 documentation rather than generic WACOGIKEN servo manuals.
The unit has two accessible adjustment points:
VR1
VR2
The surrounding markings include:
RDY / AO
SPV / A1
Because these adjustments can affect servo characteristics or analogue settings, they should not be changed randomly during troubleshooting.
Always record original positions before any adjustment and follow the correct service procedure.
The photographed terminal strip clearly marks:
U
V
W
under the motor section.
These are the three-phase servo-motor output terminals.
The drive regulates this output to control actuator motor torque, speed and position according to the governor command.
Incorrect motor wiring can result in abnormal movement, drive fault or possible equipment damage.
The drive also shows:
L1
L2
L3
for AC power input.
Because this is a high-energy servo amplifier, any voltage checks or wiring work should be carried out only by qualified technicians using the correct system documentation.
The separate:
L1C
L2C
terminals indicate control-electronics power connections.
This allows the servo-control circuitry and main motor-power section to be managed separately depending on system design.
The terminals:
RB1
RB2
are associated with the regenerative/braking resistor circuit.
Servo motors can return energy to the drive during rapid deceleration or when resisting mechanical movement.
A braking resistor dissipates this energy safely.
A damaged/open braking circuit can cause drive alarms under dynamic engine-governor movement.
Official Nabtesco MG-800 documentation lists several actuator sizes:
EAR-20 – max output 56 N·m
EAR-120 – max output 330 N·m
EAR-500A – max output 960 N·m
EAR-1000A – max output 1310 N·m.
The appropriate servo-driver configuration depends on the actuator and engine application.
Therefore, when sourcing a GPAr-24NTS, buyers should also provide the EAR actuator model.
The GPAr-24NTS is relevant to large two-stroke main-engine electronic governor systems.
Nabtesco’s MG-800 was approved for applications involving major marine engine manufacturers including MAN Diesel and Wärtsilä Switzerland.
Documented engine-operation manuals also show MG-800 installations on Wärtsilä/Sulzer low-speed main engines.
Typical applications include:
Main propulsion diesel engine
Fuel-rack governor control
Main engine RPM regulation
Electronic speed governor
Remote propulsion control integration
Check:
control power
main input power
servo enable signals
sensor feedback
CN1/CN2 connector seating
before replacing the unit.
A missing feedback or enable signal may prevent the drive entering READY status.
The fault can originate from several sections:
speed-order signal
MG-800 control unit
GPAr servo drive
feedback sensor
EAR actuator
mechanical fuel linkage
Check the full governor chain rather than automatically replacing the servo amplifier.
Verify whether the GPAr has correct input power and receives a command.
Then inspect:
U/V/W motor output
CN2 feedback
motor cable
actuator mechanical condition
If command and feedback are correct but no motor output exists, the servo drive may require repair.
Hunting may be caused by:
servo-drive instability
actuator mechanical backlash
incorrect feedback
governor tuning
fuel linkage resistance
engine operating condition
Nabtesco states that MG-800 includes automatic PID selection and anti-jiggling functions to maintain stable control.
Therefore hunting should be diagnosed as a complete system issue, not automatically attributed to the GPAr.
Inspect:
braking resistor circuit RB1/RB2
motor load
actuator binding
power supply
Rapid servo deceleration can place significant energy into the regenerative circuit.
Check:
CN3 connector
cable condition
grounding
associated controller/service interface
before condemning the main drive PCB.
Check the CN2 circuit carefully.
A failed or intermittent sensor can make an otherwise functional servo amplifier appear defective.
Inspect:
connector pins
cable shielding
continuity
sensor condition
mechanical actuator feedback arrangement
Common ageing/failure areas in older high-power servo drives can include:
power semiconductor section
electrolytic capacitors
gate-drive circuits
internal power supply
feedback circuits
connector solder joints
Component-level repair should only be done by qualified servo-electronics specialists followed by proper bench and system testing.
Nabtesco's own 2025 maintenance notice states that the MG-800 electronic governor system should receive periodic maintenance.
The company recommends:
General inspection every 2.5 years
CPU boards and power-supply components every 5 years
Actuator drive unit servo drivers every 7.5 years
LCD displays approximately every 10 years.
This is especially important for the GPAr-24NTS page because the official maintenance guidance specifically recognizes servo-driver replacement as a planned MG-800 lifecycle requirement.
Before ordering a replacement, provide:
Servo Driver Model: GPAr-24NTS
Manufacturer: WACOGIKEN
Governor System: Nabtesco MG-800
Actuator Model: EAR-20 / EAR-120 / EAR-500A / EAR-1000A or exact installed unit
ADU Model / System Reference
Main Engine Maker & Model
Original connector arrangement
Front/rear nameplate photographs
Existing drive parameters/settings if available
Fault description
Matching only “GPAr-24” is not enough.
The NTS-specific version should be matched.
SM MARINE SERVICE™ supports sourcing and supply of WACOGIKEN GPAr-24NTS Servo Drivers and Nabtesco MG-800 Governor System spare parts.
Depending on availability, equipment may be supplied as:
New / New Old Stock
Used Tested Working
Refurbished
Reconditioned
Related requirements may include:
GPAr-24NTS Servo Driver
GPAR-40NTS Servo Driver
MG-800 Governor Control Unit
Actuator Drive Unit
EAR-20
EAR-120
EAR-500A
EAR-1000A
Pulse Generator
Nabtesco / NABCO Main Engine Remote Control Components
For marine governor and engine-control spares, customers can visit SM MARINE SERVICE™.
MG-800 governor systems remain installed on operating merchant ships.
Nabtesco still provides maintenance guidance specifically for MG-800 systems, including periodic replacement of actuator-drive servo drivers, showing that continued service of these legacy governors remains an active requirement.
Replacing the correct servo drive can be considerably more practical than converting the vessel to an entirely new governor system, particularly when the:
control unit
actuator
engine linkage
remote-control system
remain serviceable.
The most useful related search references for buyers are:
WACOGIKEN GPAr-24NTS
WACOGIKEN GPAR-40NTS
Nabtesco MG-800
Nabtesco MG-800-II / MG-800-III
ADU-120A / ADU-120-R
EAR-20
EAR-120
EAR-500A
EAR-1000A
A current marine spares database also lists MG-800-II, MG-800-III, EAR-120 and ADU-120-R as related Nabtesco governor/actuator components.
These related terms help broaden SEO reach while keeping the blog technically relevant.
GPAr-24NTS is an AC Servo Driver / Servo Amplifier. Marine-market references identify the exact model as a servo-drive unit for the Nabtesco MG-800 marine main-engine governor.
Yes. Exact-model marine replacement listings specifically associate GPAR-24NTS with the MG-800 main-engine governor.
It controls electrical power to the governor actuator motor according to commands from the electronic governor control system.
They are the servo-motor output connections visible on the GPAr-24NTS.
They are main AC power-input terminals on the photographed drive.
They are regenerative/braking-resistor circuit terminals.
CN2 is labelled SEN., indicating the servo feedback/sensor interface.
CN3 is marked COM., indicating a communication/service interface.
A documented related model is GPAR-40NTS, also listed for Nabtesco MG-800 governor systems.
Nabtesco documentation identifies actuator families including EAR-20, EAR-120, EAR-500A and EAR-1000A.
ADU-120A is documented as an Actuator Drive Unit in one MG-800 governor configuration using an EAR-120 actuator.
This should not be assumed. WACOGIKEN documents GPX2 as a newer successor family to older GPAR products, but the marine NTS version, wiring, parameters, connectors and MG-800 system compatibility require engineering verification.
Nabtesco’s maintenance guidance recommends replacement of actuator-drive servo drivers at approximately 7.5-year intervals as part of MG-800 lifecycle maintenance.
Depending on failure type, specialist component-level repair may be possible, but the unit should be fully tested under appropriate servo/load conditions before shipboard reuse.
SM MARINE SERVICE™ can support worldwide sourcing of GPAr-24NTS, GPAR-40NTS and related Nabtesco MG-800 marine governor spare parts, subject to current availability.
WACOGIKEN GPAr-24NTS AC Hi Servo is a marine servo driver / servo amplifier documented for use with the Nabtesco MG-800 main-engine electronic governor system. The drive interfaces with the governor control and actuator system through I/O, sensor and communication connections and provides controlled motor output through U/V/W terminals. Related Nabtesco components include ADU-120A, EAR-20, EAR-120, EAR-500A and EAR-1000A, while GPAR-40NTS is another related MG-800 servo-drive reference. Nabtesco recommends periodic lifecycle replacement of MG-800 actuator-drive servo drivers. SM MARINE SERVICE™ supplies new, used, refurbished and reconditioned WACOGIKEN/Nabtesco governor spare parts worldwide.
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