The MR-J3-20A is Mitsubishi Electric’s 200 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, widely installed in active manufacturing equipment and in sustained demand for maintenance replacement in operational MR-J3-based servo systems where platform migration is not currently planned. As a discontinued but extensively field-installed product, the MR-J3-20A represents one of the most commonly sourced legacy servo amplifiers in the industrial automation aftermarket. Atlantech Drives holds stock of the MR-J3-20A. Contact us for fast worldwide delivery and competitive pricing.
What Is the MR-J3-20A?
The MR-J3-20A is a MELSERVO-J3 series servo amplifier providing 200 W (0.2 kW) continuous output power for Mitsubishi HC-KFS23, HC-MFS23, and equivalent 200 W servo motors equipped with the MELSERVO-J3’s 17-bit multi-turn absolute encoder (131,072 pulses/rev). The «A» suffix designates the pulse train input variant — the MR-J3-20A accepts position command pulses from a host controller via open-collector or differential RS-422A pulse input at up to 4 Mpps, with the pulse count interpreted as a position command and pulse frequency as speed command. The amplifier implements the MELSERVO-J3’s servo control architecture with 2 kHz current loop bandwidth, auto-tuning via MR Configurator or MR Configurator2 (both compatible), and the J3-series Advanced Vibration Suppression Control (AVSC, first generation). The MR-J3-20A’s built-in STO function is not present — safety compliance in MR-J3 installations relies on external safety contactors rather than the amplifier’s internal safety function. The MR-J3-20A has been superseded by the MR-J4-20A (200 W, 22-bit encoder, built-in STO) and should be specified as maintenance replacement only.
Key Technical Specifications
- Model: MR-J3-20A
- Rated Output Power: 200 W (0.2 kW)
- Power Supply: 200–240 VAC single-phase or three-phase, 50/60 Hz
- Continuous Output Current: 1.5 A
- Maximum Output Current: 4.5 A (3× continuous peak)
- Compatible Servo Motors: HC-KFS23, HC-MFS23, HG-KR23 (J4 motor, 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. 0.8 kg
Series Comparison & Selection Guide
The MR-J3-20A belongs to Mitsubishi’s MELSERVO-J3 generation, which was superseded by the MELSERVO-J4 (MR-J4-20A) from approximately 2013 onward. The MR-J4-20A provides 22-bit encoder resolution (versus 17-bit for MR-J3-20A), built-in STO safety function (versus external contactor requirement), AVSC II (versus AVSC I), and improved auto-tuning convergence. For new designs, the MR-J4-20A or the current MR-J4E-20A (iQ-R compatible) should be specified. The MR-J3-20A is appropriate only for direct maintenance replacement in existing MR-J3 installations where: the existing HC-KFS23 or HC-MFS23 servo motor is being retained (not replaced), the host controller’s pulse train output cable wiring is being reused without modification, and upgrading to MR-J4 is deferred. In some cases, the MR-J4-20A can directly replace the MR-J3-20A even with the original HC-series motor, as the MR-J4 supports J3 motor compatibility mode via parameter PA22 — enabling amplifier-only upgrade without motor replacement. Verify this compatibility via Mitsubishi’s servo compatibility matrix before specifying the MR-J4-20A as a drop-in replacement.
Troubleshooting Guide
For MR-J3-20A amplifiers generating AL.16 (encoder error) alarms, the most common causes are encoder cable damage and encoder battery depletion. Inspect the encoder cable (CN2) for jacket cracking, especially at the motor connector where the cable exits — the encoder cable’s repeated flexing during axis motion fatigues the cable jacket and individual conductors at the bend point, causing intermittent AL.16 as conductors begin to fail. Replace encoder cables showing any visible jacket damage even if the amplifier is still operating intermittently — a partially failed encoder cable can cause unexpected axis runaway if the encoder feedback is lost at a critical moment during machine operation. Verify the encoder battery voltage via MR Configurator2’s diagnostic display — AL.25 (absolute position erased) occurs when the battery voltage drops below the minimum threshold, requiring a new homing cycle after battery replacement. For AL.30 (regenerative overvoltage) alarms occurring unexpectedly, verify the supply voltage is not elevated above 240 VAC — an overvoltage supply causes a higher DC bus voltage that reduces the headroom before the regenerative overvoltage trip threshold is reached, causing spurious AL.30 on deceleration. For AL.37 (parameter error) alarms after replacing a MR-J3-20A with a new unit, the replacement amplifier ships with factory default parameters — the machine-specific servo parameters (gain settings, motor code, encoder type) must be written to the replacement amplifier before the servo can operate correctly.
Frequently Asked Questions
Q: Can the MR-J3-20A’s 17-bit encoder be upgraded to 22-bit resolution without replacing the amplifier?
A: No. The encoder resolution is determined by the servo motor’s built-in encoder, not the amplifier. Upgrading from 17-bit to 22-bit resolution requires replacing the servo motor with a current-generation HG-KR or HG-MR series motor equipped with the 22-bit absolute encoder, combined with replacing the MR-J3-20A amplifier with the MR-J4-20A. The MR-J3-20A’s encoder interface is not compatible with 22-bit encoders.
Q: Is the MR-J3-20A still available as a new product, or only as old stock?
A: The MR-J3 series has been discontinued from Mitsubishi production. The MR-J3-20A is available only from distributor inventory and specialist aftermarket suppliers including Atlantech Drives. When sourcing MR-J3-20A for maintenance replacement, verify the supplier’s warranty terms and product authenticity — genuine Mitsubishi MR-J3-20A units can be identified by the Mitsubishi logo, serial number format, and firmware version visible in MR Configurator2 after connection.
Q: Can the MR-J3-20A be programmed with MR Configurator2, or does it require the older MR Configurator software?
A: Both MR Configurator (the original J3-era software) and MR Configurator2 (the current unified software) are compatible with the MR-J3-20A for parameter setting, auto-tuning, and waveform monitoring via USB. MR Configurator2 is the recommended tool as it supports both MR-J3 and MR-J4 amplifiers in the same software environment, simplifying parameter management in facilities operating both J3 and J4 servo systems.
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