The MR-J3-40A is Mitsubishi Electric’s 400 W MELSERVO-J3 series servo amplifier for 200 V single-phase or three-phase AC power supply with pulse train position command input — a legacy servo amplifier from Mitsubishi’s third-generation MELSERVO platform, providing 400 W continuous servo control for HC-KFS43 and HC-MFS43 series servo motors in active MR-J3-based machinery where maintenance replacement is required without platform migration. The MR-J3-40A is available through Atlantech Drives — quote within 24-48 hours, worldwide express shipping, 12-month warranty.
What Is the MR-J3-40A?
The MR-J3-40A is a MELSERVO-J3 series servo amplifier providing 400 W (0.4 kW) continuous output power for Mitsubishi HC-KFS43, HC-MFS43, and equivalent 400 W servo motors with the MR-J3’s 17-bit multi-turn absolute encoder. The «40» in the model designation denotes the 400 W power class — identical in architecture to the MR-J3-20A but with a larger power stage rated for 3.0 A continuous output current versus 1.5 A for the 200 W model. The MR-J3-40A accepts position command pulses via open-collector or differential RS-422A pulse input at up to 4 Mpps, interpreting the pulse train as position and speed commands within the MELSERVO-J3 servo control architecture with 2 kHz current loop bandwidth. The amplifier shares the same 40 mm compact housing width as the MR-J3-20A, maintaining panel layout consistency in multi-axis MR-J3 installations where different axis power requirements are served by amplifiers of the same physical footprint. Like the MR-J3-20A, the MR-J3-40A does not include a built-in STO safety function — safety requirements are met via external safety contactors in the main circuit wiring.
Key Technical Specifications
- Model: MR-J3-40A
- Rated Output Power: 400 W (0.4 kW)
- Power Supply: 200–240 VAC single-phase or three-phase, 50/60 Hz
- Continuous Output Current: 3.0 A
- Maximum Output Current: 9.0 A (3× continuous peak)
- Compatible Servo Motors: HC-KFS43, HC-MFS43, HG-KR43 (J4 motor in J3 compatibility mode)
- Command Interface: Pulse train input (open-collector or differential RS-422A)
- Maximum Input Pulse Frequency: 4 Mpps (differential), 200 kpps (open-collector)
- Encoder Interface: Serial 17-bit absolute encoder (131,072 pulses/rev)
- Safety Function: None built-in (external safety contactor required)
- Regenerative Brake: Built-in
- Communication: USB (MR Configurator2), RS-422 (multi-axis)
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 40 mm × 150 mm × 138 mm
- Weight: Approx. 0.9 kg
Compatibility & System Integration
The MR-J3-40A is compatible with any host controller capable of generating differential or open-collector pulse train output — Mitsubishi QD75MH4 and QD75D4 MELSEC-Q positioning modules, FX2N-1PG-E and FX2N-10PG FX2N positioning modules, FX3U-1PG and FX3U-2PG FX3U positioning adapters, and third-party CNC controllers and motion controllers with pulse train output. For GX Works2 parameter configuration and servo tuning, the MR-J3-40A connects via USB using MR Configurator2 — both the legacy MR Configurator and the current MR Configurator2 fully support the MR-J3 parameter set. In a mixed-age servo system where some axes use MR-J3-40A and others have been upgraded to MR-J4-40A, MR Configurator2 manages parameters for both generations from the same application, simplifying maintenance programming. The MR-J3-40A is compatible with Mitsubishi’s HC-KFS43 and HC-MFS43 servo motors — current-generation HG-KR43 motors (MR-J4 standard) can also be used with the MR-J3-40A in motor compatibility mode (parameter PA22 = 1), enabling motor-only or amplifier-only upgrades as separate maintenance phases rather than requiring simultaneous replacement. For RS-422 multi-axis cascade connection (MR-J3-40A → MR-J3-20A → … chain for simultaneous parameter programming from one MR Configurator2 session), use the MR-J3-series cascade cable (MR-J3ENCBL05M-A1-L or equivalent) — this cascade wiring allows all amplifiers in a multi-axis panel to be configured from a single USB connection to the first amplifier in the chain.
Replacement & Upgrade Notes
The MR-J3-40A has been discontinued from Mitsubishi production and is available only from aftermarket inventory. When a direct MR-J3-40A replacement cannot be sourced, the MR-J4-40A provides a functional upgrade path — the MR-J4-40A accepts the same HC-KFS43 and HC-MFS43 motors in J3 motor compatibility mode (PA22 = 1), accepts the same pulse train command wiring, and is physically compatible with the same panel space as the MR-J3-40A (same 40 mm housing width, same mounting hole pattern). The MR-J4-40A upgrade provides 22-bit encoder resolution (versus 17-bit), built-in STO, AVSC II, and improved auto-tuning — benefits beyond the maintenance replacement justification that may also satisfy pending machinery directive safety compliance requirements for the affected axis. When replacing MR-J3-40A with MR-J4-40A, transfer the existing MR-J3-40A servo parameters to MR-J4 format using MR Configurator2’s parameter conversion function, then re-run one-touch auto-tuning with the converted parameters as the starting point. For facilities with large fleets of MR-J3-40A units across many machines, plan a rolling upgrade programme rather than reactive maintenance replacements — the MR-J3’s discontinued status and increasing scarcity of spare parts makes proactive fleet migration to MR-J4 more economical than emergency sourcing at premium prices when individual units fail.
Frequently Asked Questions
Q: What is the difference between the MR-J3-40A and the MR-J3-40B in terms of application?
A: The MR-J3-40A uses pulse train input (open-collector or differential RS-422A) from an external positioning module or CNC controller, while the MR-J3-40B uses SSCNET III optical fibre network communication from a MELSEC-Q motion controller (Q172DSCPU, Q173DSCPU). Both provide 400 W continuous output power from the same power stage. Select the MR-J3-40A for systems with pulse train host controllers; select the MR-J3-40B for systems with SSCNET III motion controllers. Both are legacy products superseded by the MR-J4 series.
Q: Can an MR-J3-40A with a failed encoder battery still operate in incremental encoder mode after homing?
A: Yes. If the MR-J3-40A’s encoder battery has depleted and the absolute position has been lost, the amplifier can operate in an incremental-equivalent mode after performing a homing cycle at machine power-up — the absolute multi-turn position counter is re-established at the home sensor position, and the axis operates normally until the next power-off event, at which point homing must be repeated. This mode is acceptable for machines that always home at power-up as part of their standard start sequence. Replace the encoder battery as soon as possible after this condition is detected — continued operation with a depleted battery risks complete encoder data loss if the motor is moved after power-off.
Q: Is the MR-J3-40A compatible with the FX3U-20SSC-H SSCNET III/H adapter?
A: No. The FX3U-20SSC-H uses SSCNET III/H protocol, which is incompatible with the MR-J3-40A’s SSCNET III interface. The MR-J3-40B (SSCNET III variant) is compatible with the Q172DSCPU SSCNET III controller, while the FX3U-20SSC-H requires MR-J4-B (SSCNET III/H) amplifiers. The MR-J3-40A (pulse train) is controlled by the FX3U-2PG positioning adapter, not by the SSCNET III/H FX3U-20SSC-H.
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