31.07.2025 by Viktor Siebert
Repair Report, Mitsubishi HC53S-A42 or HC53S-SZ AC Servo Motor
Discontinued, but Still in Use, Challenges for Operators and OEMs.
The Mitsubishi HC53S-A42 (HC53S-SZ) belongs to a servo motor series that has been officially discontinued by Mitsubishi Electric. One of the main issues: Mitsubishi does not offer any repair services for servo motors, not directly and not through authorized partners. Spare parts are limited and come at a high price. For example, the corresponding absolute encoder OSA104S2 costs over €2700 as a single part.
Some machine builders still offer replacement motors to their end customers, but these are primarily targeted toward OEM-level service and are not always economically viable, especially for older systems where a full motor replacement is not justifiable.
Weak Point: The Encoder
The motor was sent in with repeated overcurrent alarms and occasional A.05 encoder error messages. A closer inspection confirmed the root cause: Oil and coolant emulsions had entered the motor through the rear shaft seal and contaminated the encoder. The resulting corrosion led to unstable signals and communication faults.
The OSA104S2 encoder is a serial absolute encoder that transmits data via synchronous serial communication. Contrary to some assumptions, this model does not use fiber-optic technology.
Our Solution Encoder Refurbishment Instead of Replacement
Over the past years, we have specialized in the diagnosis and repair of Mitsubishi encoders, especially those used in HC, SF, and MF series servo motors. Based on many cases, we developed a standardized in-house process to refurbish encoders like the OSA104S2. This makes repairs economically feasible again for our customers.
The refurbishment includes the following steps:
- Full disassembly of the encoder
- Cleaning of electronic components and removal of corrosion
- Replacement of damaged parts and internal connectors
- Testing of signal logic and reference alignment
- Resealing of the housing with new gaskets
- Simulation of serial data communication with original drives
- Final calibration and test run under real operating conditions
Even severely contaminated or defective encoders can be restored to full function at a fraction of the cost of a new unit.
Motor Repair and Testing
After initial diagnosis, the motor was fully dismantled and reconditioned. The winding was thermally dried and insulation-tested; bearings were replaced, and the rear seal was renewed. All housing components were carefully cleaned and reassembled.
The repaired motor was then tested on our in house Mitsubishi test bench. It was operated with an original MR-J2S drive under various load profiles and monitored for encoder performance and communication stability. All parameters were within the expected range.
Outcome
After repair, the motor functioned flawlessly. Encoder signals were stable, and no further overcurrent or A.05 alarms occurred. By refurbishing the encoder and restoring full mechanical and electrical integrity, the customer avoided a costly replacement and extended the motor’s service life.
This case shows how legacy Mitsubishi servo motors can still be maintained cost-effectively, even long after official support has ended, providing both technical reliability and significant savings.
To mentioned Mitsubishi Motor: Mitsubishi HC53S-A42 AC-Servomotor
More details about our Mitsubishi repair services can be found here:
Mitsubishi motor Repair by Industrypart
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Technical Specifications
| Parameter | Value |
|---|
| Model | HC53S-SZ / HC53S-A42 |
| Motor Type | AC Servo Motor |
| Rated Power | 0.5 kW |
| Rated Voltage | 3-phase 127 V |
| Rated Current | 3.2 A |
| Rated Speed | 3000 rpm |
| Encoder Type | OSA104S2 (Absolute Encoder) |
| Encoder Resolution | 131072 pulses/rev (17-bit) |
| Communication Type | Serial synchronous data transmission |
| Protection Class | IP65 |
| Insulation Class | F (IEC60034-1) |
| Weight | approx. 5.0 kg |
| Cooling Method | Self-cooled, fully enclosed |
| Country of Origin | Japan (Mitsubishi Electric Corp.) |
Operating Environment and Integration
This motor is typically used in CNC systems and automation equipment. It is compatible with Mitsubishi servo amplifiers such as the MDS, MR-J2S and MR-J3 series.
Environmental Conditions:
| Condition | Specification |
|---|
| Ambient Temperature | 0–40 °C (in operation), non-condensing |
| Storage Temperature | -15–70 °C, non-freezing |
| Humidity | max. 80% RH (non-condensing) |
| Installation Site | Indoor use only, no direct sunlight |
| Altitude Limit | max. 1000 meters above sea level |
| Vibration Limit | max. 49 m/s² (depending on mounting) |
Common Faults and Troubleshooting
| Alarm Code | Description | Possible Cause | Recommended Action |
|---|
| A.05 | Encoder signal error | Corrosion, damaged encoder, bad connector | Clean or replace encoder, check cabling |
| Overcurrent | Excessive load or feedback | Shaft blockage, encoder mismatch | Inspect windings, bearings, encoder function |
Component Overview
| Component | Description |
|---|
| Shaft (Ø 14h6) | Precision-machined steel with optional keyway |
| Encoder | OSA104S2 absolute encoder with serial communication |
| Rear Cover | Contains seal and access to encoder housing |
| Motor Housing | Fully enclosed, ribbed aluminum body |
| Connectors | U/V/W power leads, PE, encoder signal connector |
| Bearings | Deep groove ball bearings, both ends |
| Shaft Seal | Rubber-lipped radial shaft seal |
Summary
The Mitsubishi HC53S-A42 motor is a mid-inertia servo unit with high encoder resolution and robust mechanical design. Although officially discontinued, its solid performance and high compatibility make it a valuable asset in older CNC systems. Through targeted encoder refurbishment and component-level service, motors like this can be returned to reliable operating condition, offering significant cost advantages over replacement.