MR-J4-100B Guide: Mitsubishi MELSERVO J4 1kW Servo Drive Setup

Overview

The MR-J4-100B is a 1kW AC servo amplifier in Mitsubishi's MELSERVO-J4 series. It drives a single 1kW-class HG-series servo motor and receives its commands over SSCNET III, the optical servo network that links Mitsubishi motion controllers to their axes. In a typical cabinet the amplifier sits between lighter 70B axes and heavier 200B axes on the same network, taking its share of the fiber loop and reporting status on the front display, with AL.xx alarm codes explained in the MR-J4 amplifier manual. Physically it shares the J4-B cabinet format, so it mounts alongside its 70B and 200B siblings as the manual's installation section describes.

The catalog number reads as follows. MR is the MELSERVO servo prefix. J4 identifies the J4 generation of the servo family, the successor to the J2-S and J3 lines. The number 100 sets the capacity class at 1kW, which fixes the motor the amplifier is meant to drive. The trailing B marks the SSCNET III interface variant, so commands arrive as network data from a motion controller instead of a pulse train, and the network connection is optical fiber. Taken together, the number names a current-generation Mitsubishi servo amplifier sized for one 1kW axis on the SSCNET III network.

The capacity ladder in the J4 series

Within one generation the J4-B line steps through capacity classes, and the three sizes below cover most mid-range motion axes. The differences are electrical sizing and motor class; the interface, network, and commissioning workflow stay the same across the ladder.

Pick the class that matches the motor's rated output on its nameplate, and when in doubt, the machine's parts list settles it. Oversizing an amplifier for a smaller motor brings no benefit and leaves the axis record inconsistent with the project, while undersizing trips the drive under load. When a machine mixes classes, each amplifier holds its own capacity class on the same loop, so the ladder scales without redesigning the network.

Pairing the amplifier with the motor

The 1kW class of the HG series comes in different inertia frames, and the machine's builder chose one of them for a reason. A low inertia frame accelerates fast and suits pick-and-place style duty; a medium inertia frame handles smoother, heavier motion. The replacement amplifier does not care which frame it drives as long as the class matches, but the controller project records the motor type, and keeping the original motor keeps that record honest.

Check the encoder cable when the motor stays and the amplifier changes. HG-series motors use the encoder arrangement described in the MR-J4 manual, and the amplifier's encoder connection, along with the encoder battery for absolute position machines, needs to be re-landed correctly. After a replacement with battery-backed position, expect to perform the homing procedure from the controller side before the machine produces parts again.

Ordering gets one extra check at this class: the label. Photographs of the old unit's label, capacity class, and connector layout travel with the purchase request, and the replacement gets compared against them on arrival. A part number one character off arrives boxed like the right answer and still burns a service window.

Putting a fresh unit into service

Installation follows the manual's terminal diagrams: supply on the power input, motor and encoder cables to their connectors, brake wiring where the motor has a brake, and the two optical network ports in the loop's order. Keep fiber runs short and strain-relieved, and keep them clear of the motor power wiring. Warning: disconnect all power and follow your lockout and tagout procedure before working on the power terminals, because stored charge inside the amplifier persists after shutdown and the manual specifies the wait.

First power-up should be quiet: no alarm on the display and no motion until the controller asks for it. From there, commissioning runs through MR Configurator2 on a PC and the controller project. Bring the axis on, confirm direction with a short slow move, run one-touch tuning so the drive learns the machine, and then step up to production speed. On networked axes the command scaling lives in the controller, so verifying a known travel distance against a scale or dial confirms the whole chain before the machine returns to work.

Multi-axis machines get commissioned one axis at a time. A mistake on one axis cannot hide behind motion on another, and a fault that appears during a single-axis move points at that axis's wiring alone.

Common issues and troubleshooting

Most service calls on this class fall into the rows below. Display codes always outrank guesses: look any AL.xx code up in the MR-J4 amplifier manual, which lists each one with its meaning and corrective action.

When a fault resists the table, split the problem in half at the cables. A bench session with a known-good fiber and a known-good encoder cable separates an amplifier fault from a wiring fault in one round, and it is faster than a second opinion on the drive itself. Keep the packing until the machine has run a week, so a unit that fails early goes back in its original box with the labels intact.

FAQ

Can I swap an MR-J4-70B for an MR-J4-100B on the same axis?

Not as a like-for-like replacement. The capacity class must match the motor's rated output, so a 750W motor keeps a 70B and a 1kW motor needs a 100B. The controller project also records the motor per axis, and the machine's parts list reflects the class it was built with.

Does the MR-J4-100B work with the original SSCNET?

No. This model carries SSCNET III, and the motion controller's interface has to match. A controller equipped for SSCNET III recognizes the amplifier on the fiber loop; the older network belongs to the earlier J2-S generation of drives.

What does a replacement amplifier lose compared with the old unit?

Tuning and any locally stored settings, since parameters live in the drive and a fresh unit starts from defaults. Axis configuration, command scaling, and the machine's motion programs live on the controller side and survive the amplifier swap, which is why commissioning is usually a short pass.