Mitsubishi HG-KN73BJ-S100 Replacement for MELSERVO-J4

Product Overview

Mitsubishi HG-KN73BJ-S100 Replacement for MELSERVO-J4: Smooth Transition & Legacy System Compatibility

The Mitsubishi HG-KN73BJ-S100 is a 750W AC servo motor from the MELSERVO-J4 series, designed for high-precision motion control in industrial automation systems. Whether your existing HG-KN73BJ-S100 has reached end-of-life, suffered mechanical failure, or your facility is migrating from an older servo platform, this replacement unit provides a direct, validated upgrade path with minimal disruption to your production line.

Many facilities running legacy Mitsubishi servo systems — including older MR-J2S, MR-J3, and early MR-J4 configurations — face increasing difficulty sourcing original spare parts. The HG-KN73BJ-S100 is a proven drop-in replacement that maintains full compatibility with the MR-J4 servo amplifier family, preserving your existing wiring harness, encoder cable routing, and motor mounting footprint. The -S100 shaft specification (key-way, 14mm diameter) matches the mechanical interface of most legacy HG-KN series installations, eliminating the need for coupling adapters or bracket modifications during retrofit.

When migrating from an MR-J2S-70A or MR-J3-70A amplifier to the current MR-J4-70A, the HG-KN73BJ-S100 serves as the recommended motor pairing. The transition involves updating the servo parameter settings via MR Configurator2 software, re-mapping the I/O signal assignments on the CN1 connector, and verifying the regenerative option — typically an MR-RB032 or MR-RB12 — is correctly rated for the new amplifier. In most cases, the existing 200VAC single-phase or three-phase power supply wiring requires no modification.

For systems integrated into a broader Mitsubishi iQ-R or iQ-F PLC architecture, the HG-KN73BJ-S100 communicates with the motion controller via SSCNET III/H optical network through the MR-J4 amplifier, maintaining deterministic 0.888ms cycle synchronization. If your facility is upgrading from a Q-series MELSEC PLC with SSCNET II cabling, the migration to SSCNET III/H requires replacing the servo amplifier and updating the motion program in GX Works3, while the motor itself — including the HG-KN73BJ-S100 — remains mechanically and electrically unchanged.

Compatibility Comparison Table

Seamless Upgrade Solutions

A complete servo axis migration typically involves more than the motor alone. When replacing the HG-KN73BJ-S100 in an existing control cabinet, engineers commonly source the MR-J4-70A servo amplifier as the matched drive unit, ensuring full SSCNET III/H compatibility and access to advanced tuning functions such as One-touch Tuning and Machine Resonance Suppression Filter. The amplifier mounts on a standard DIN rail within the same cabinet footprint as the outgoing MR-J3-70A, minimizing panel re-layout work.

For multi-axis systems, the MR-J4W2-44B dual-axis amplifier offers a compact alternative when two 400W–750W axes share a single cabinet slot, reducing wiring complexity and heat dissipation requirements. Encoder cable replacement is often necessary during motor swap; the MR-J3ENCBL5M-A1-L or equivalent J4-series encoder cable should be verified for length and connector type before installation.

Power supply integrity is critical during commissioning. The MR-PWS1CBL3M-A1-L power connector cable and a correctly rated MR-RB032 regenerative resistor should be confirmed as part of the bill of materials for any HG-KN73BJ-S100 retrofit. In applications with frequent deceleration cycles — such as packaging machinery or press feeders — an external regenerative option prevents amplifier overvoltage faults during the transition period.

For facilities integrating the servo axis into a Mitsubishi iQ-R motion system, the RD77MS4 Simple Motion Module or RD77GF4 SSCNET III/H network module provides the controller-side interface. Parameter migration from Q172DSCPU or Q173DSCPU motion controllers to the iQ-R platform requires re-mapping axis parameters in GX Works3, but the physical motor — the HG-KN73BJ-S100 — requires no modification. Terminal block modules such as the MR-TB50 simplify I/O signal wiring during panel re-termination, reducing the risk of wiring errors on CN1 and CN3 connectors.

Retrofit Guidance FAQ

Q: Can I connect the HG-KN73BJ-S100 directly to my existing MR-J3-70A amplifier?
A: No. The HG-KN73BJ-S100 uses a 22-bit absolute encoder interface that is not backward-compatible with MR-J3 amplifiers. You must upgrade to an MR-J4-70A amplifier. The motor’s mechanical interface (flange, shaft, and cable exit) is unchanged, so the mechanical installation is a direct swap.

Q: Will my existing wiring harness work?
A: The power cable connector (MS3102A18-10P or equivalent) is compatible. The encoder cable connector differs between J3 and J4 series — a new J4-compatible encoder cable is required. Verify cable length against your existing routing path before ordering.

Q: Do I need to re-tune the servo after replacement?
A: Basic parameters (electronic gear ratio, position loop gain) should be re-verified. The MR-J4 amplifier’s One-touch Tuning function significantly reduces commissioning time. If replacing a like-for-like HG-KN73BJ-S100 on an existing MR-J4 amplifier, parameter backup and restore via MR Configurator2 is sufficient in most cases.

Q: Is the mounting footprint identical to the HG-KN73J?
A: Yes. The 80mm square flange and M5 bolt pattern are identical. The overall motor length may vary slightly between sub-variants; verify the rear shaft protrusion clearance in confined cabinet installations.

Q: What communication protocol does this motor support?
A: The HG-KN73BJ-S100 itself does not communicate independently — all communication is handled by the paired MR-J4 servo amplifier via SSCNET III/H optical fiber to the motion controller. No additional protocol configuration is required at the motor level.

Warranty Assurance

Every HG-KN73BJ-S100 unit shipped by TOPNLMS is covered by a 12-month warranty from the date of delivery. Prior to dispatch, each unit undergoes functional verification including insulation resistance testing, encoder signal integrity check, and rotational run-in inspection. Units are packed in anti-static foam with original or equivalent protective packaging to prevent transit damage.

In the event of a confirmed defect within the warranty period, TOPNLMS provides replacement dispatch within 3 business days of fault confirmation. Our technical support team is available to assist with installation queries, parameter configuration guidance, and compatibility verification before and after purchase. We maintain stock of HG-KN73BJ-S100 and related MR-J4 series components to support urgent breakdown replacement requirements with short lead times.

For volume procurement, OEM integration projects, or scheduled maintenance contracts requiring multiple units, please contact our sales team directly for pricing, lead time confirmation, and documentation packages including test reports and certificates of conformity.