The MR-J2S-20B is Mitsubishi Electric’s 200 W MELSERVO-J2 Super series servo amplifier for 200 V single-phase or three-phase AC power supply with SSCNET optical fibre network interface — a legacy servo amplifier from Mitsubishi’s second-generation MELSERVO Super platform, providing 200 W continuous servo control via SSCNET (the first-generation Mitsubishi servo network, predecessor to SSCNET III) for HC-KFS23 and HC-MFS23 series servo motors in active J2S SSCNET-based multi-axis servo systems. Atlantech Drives holds stock of the MR-J2S-20B. Contact us for fast worldwide delivery and competitive pricing.
What Is the MR-J2S-20B?
The MR-J2S-20B is a MELSERVO-J2 Super series servo amplifier providing 200 W (0.2 kW) continuous output power via SSCNET optical fibre — the first-generation Mitsubishi servo network preceding SSCNET III (used by MR-J3-B) and SSCNET III/H (used by MR-J4-B). The «B» suffix designates the SSCNET network variant — the MR-J2S-20B receives all position and speed commands via SSCNET optical fibre at 0.888 ms communication cycle from compatible J2S-era MELSEC-Q motion controllers (Q172CPU, Q173CPU — the earlier Q-series motion CPUs distinct from the Q172DSCPU and Q173DSCPU used with MR-J3). SSCNET (original) is physically and electrically different from SSCNET III — different optical wavelength, different connector type, and different communication protocol — making MR-J2S-B amplifiers incompatible with MR-J3-B and MR-J4-B controllers and amplifiers even though all three use plastic optical fibre as the physical medium. The MR-J2S-20B’s maintenance replacement scenario is among the most complex in the Mitsubishi servo legacy product range: the amplifier requires a SSCNET (not SSCNET III) motion controller which itself is no longer manufactured, the servo motor uses a J2S-era encoder protocol incompatible with current motors, and the commissioning software is the oldest MR Configurator version.
Key Technical Specifications
- Model: MR-J2S-20B
- 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 (J2S-era motors only)
- Command Interface: SSCNET optical fibre (original SSCNET, not SSCNET III)
- Communication Cycle: 0.888 ms
- Encoder Interface: Serial encoder (J2S-era HC motor encoder protocol)
- Safety Function: None built-in
- Regenerative Brake: Built-in
- Communication: RS-232C (MR Configurator legacy software)
- Compatible Motion Controllers: Q172CPU, Q173CPU (J2S-era MELSEC-Q motion CPUs)
- Operating Temperature: 0°C to 55°C
- Dimensions (W × H × D): 40 mm × 130 mm × 120 mm
- Weight: Approx. 0.7 kg
Architecture & Design Overview
The MR-J2S-20B implements the MELSERVO-J2 Super servo control architecture with SSCNET network command interface — the first implementation of network-commanded servo control in Mitsubishi’s MELSERVO product history. The original SSCNET network uses a different optical wavelength and communication protocol from SSCNET III, with the motion controller (Q172CPU or Q173CPU) transmitting position commands to each amplifier at 0.888 ms intervals via the optical chain. The communication data rate of original SSCNET is lower than SSCNET III — the J2S SSCNET uses 5.6 Mbps transmission versus 10 Mbps for SSCNET III — and the command data structure encodes position increments and control signals in a format specific to the J2S generation that is not compatible with J3 or J4 amplifier decoding. The J2S-era motion controller (Q172CPU, Q173CPU) is itself a legacy product, discontinued well before the Q172DSCPU series that supports SSCNET III. A complete J2S SSCNET system — Q172CPU/Q173CPU motion controller, SSCNET (original) optical cables, and MR-J2S-B amplifiers — must be maintained as an integrated legacy system; upgrading any single component (controller or amplifier) to a later generation requires upgrading all components simultaneously to a consistent later generation, as the three generations of servo network are mutually incompatible. This integrated legacy architecture makes MR-J2S-20B maintenance particularly challenging — a failed MR-J2S-20B in a Q172CPU-managed SSCNET system cannot be replaced with an MR-J3-20B or MR-J4-20B, and the Q172CPU itself is also a legacy product requiring sourcing from the aftermarket if it fails.
Troubleshooting Guide
For MR-J2S-20B amplifiers generating SSCNET communication alarms, the original SSCNET optical fibre connections use a different connector type from SSCNET III — verify the specific connector type on the MR-J2S-20B (original SSCNET uses an SMA or proprietary push-pull connector depending on the specific hardware revision) and confirm the optical cable type matches the amplifier’s connector. SSCNET (original) optical cables are not interchangeable with SSCNET III plastic optical fibre cables despite both using optical fibre as the medium. For servo performance alarms (AL.50 overload, AL.16 encoder error) on MR-J2S-20B units above 15 years of age, the diagnostic approach is similar to other J2S amplifiers — inspect the encoder cable for damage, verify the encoder battery voltage, and evaluate the DC bus capacitor condition for units approaching end of capacitor rated life. For MR-J2S-20B units where MR Configurator access is not available (the legacy software tool is difficult to install on modern Windows operating systems), Mitsubishi technical support can advise on compatible OS and driver combinations for running MR Configurator on modern hardware — this access is essential for any parameter verification or servo tuning task on J2S amplifiers. If the MR-J2S-20B generates a SSCNET communication alarm immediately after the motion controller (Q172CPU/Q173CPU) is powered on, check whether the fault is in the amplifier or the motion controller by verifying that all other amplifiers in the SSCNET chain are also reporting communication errors — a Q172CPU communication failure affects all amplifiers in the chain simultaneously, while a failed MR-J2S-20B optical connector affects only that amplifier and all downstream amplifiers in the daisy-chain.
Frequently Asked Questions
Q: Can the MR-J2S-20B’s SSCNET connection be upgraded to SSCNET III by replacing only the amplifier with an MR-J3-20B?
A: No. The SSCNET and SSCNET III networks are not protocol compatible — even though both use optical fibre, the communication protocols, data rates, and connector types differ between original SSCNET (MR-J2S-B) and SSCNET III (MR-J3-B). Replacing a MR-J2S-20B with an MR-J3-20B in a Q172CPU-managed SSCNET system is not possible — the Q172CPU cannot communicate with MR-J3 amplifiers. A complete system upgrade (Q172CPU → Q172DSCPU or Q173DSCPU motion controller, MR-J2S-20B → MR-J3-20B or MR-J4-20B amplifiers, original SSCNET cables → SSCNET III POF cables) must be performed simultaneously.
Q: Is the MR-J2S-20B compatible with any currently manufactured servo motor?
A: No. The MR-J2S-20B’s encoder interface is specific to the J2S-era HC-KFS23 and HC-MFS23 motors — no currently manufactured Mitsubishi servo motor (HG-KR, HG-MR, HG-SR series) uses the J2S encoder protocol. Maintenance replacement of the MR-J2S-20B must use the same HC-KFS23 or HC-MFS23 motor from aftermarket inventory, or the complete system must be upgraded (amplifier + motor + controller + cables) to a current-generation platform.
Q: What is the most common cause of MR-J2S-20B failure in units above 15 years of service?
A: The two most common failure modes in MR-J2S-20B units above 15 years of service are DC bus electrolytic capacitor degradation (causing AL.30 regenerative overvoltage or unstable DC bus voltage during motor acceleration) and cooling fan bearing failure (causing AL.46 overtemperature alarms). Capacitor degradation is the more insidious failure as it develops gradually and may not generate alarms until the capacitor ESR has increased substantially — proactive capacitor replacement during a scheduled maintenance window is the recommended strategy for J2S units above 12 years of service.
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