25.08.2025 by Viktor Siebert
Mitsubishi HC103T-SZ / HC103T-A42 AC Servo Motor – Technical Data, Troubleshooting and Preventive Overhaul
One of our long-term customers commissioned us to fully overhaul an entire CNC machine – including all servo motors, spindle motors, and drive units. The machine was still functional, but the customer wanted to ensure long-term sustainability and reliability.
The HC103T motors were carefully disassembled. Early wear signs were visible on the bearings – not a complete failure yet, but a clear warning. The shaft seals had hardened and were no longer providing full protection, posing a risk of coolant or oil ingress.
We replaced all wear parts: bearings, seals, and connectors. The OSA104S2 encoder was dismantled, cleaned, and tested. To guarantee performance, it was also reprogrammed and recalibrated.
The motor housings were stripped, cleaned, and repainted for corrosion protection. Internally, motors were washed with emulsion, oven-dried, and then reassembled.
Finally, we tested each motor extensively:
- Insulation & hi-pot tests
- Encoder signal quality (angle error, waveform check)
- Dynamic load test with variable torque and speed
- Long-duration stress test under full load
After this process, the motors were practically in as-new condition, ensuring reliability for years to come.
Causes of Encoder or Motor Failures
- Temperature changes → condensation, corrosion
- Moisture/oil mist → encoder disk contamination
- Vibrations → bearing damage, encoder misalignment
- Aging → hardened seals, lubricant loss
- Cables/connectors → broken wires, poor contacts
Failures usually appear gradually: intermittent encoder errors, disappearing after restart, but occurring more frequently until total breakdown.
Preventive Tips for Customers
- Keep the environment dry and clean
- Inspect cables and connectors regularly
- Avoid excessive vibration
- Prevent extreme temperature changes
- Schedule preventive overhauls every 5–7 years
To mentioned Mitsubishi Motor: Mitsubishi HC103T-SZ / HC103T-A42 AC Servomotor
More details about our Mitsubishi repair services can be found here:
Mitsubishi motor Repair by Industrypart
📞 Feel free to contact us with any questions about your Mitsubishi drive technology.
Our expert team is happy to help!
Technical Specifications
| Parameter | Value |
|---|
| Model | HC103T-SZ / HC103T-A42 |
| Manufacturer | Mitsubishi Electric Corp. Japan |
| Rated Power | 1.0 kW |
| Rated Voltage | 3AC 135 V |
| Rated Current | 5.3 A |
| Rated Speed | 3000 min⁻¹ |
| Torque (approx.) | ~3.2 Nm |
| Protection Class | IP65 (Standard) |
| Insulation Class | F |
| Encoder | OSA104S2 Absolute Encoder (1M ppr) |
| Weight | ~6.5 – 7.0 kg (HC-series reference) |
| Shaft End | Taper (T) |
| Production Year | 2006 |
Application Environment & Compatible Devices
- Typical Applications
- CNC machine tools (milling, turning, machining centers)
- Automation systems requiring high precision
- Dynamic positioning and torque control tasks
- Compatible Servo Drives
- Mitsubishi MDS-B series servo drives
- MDS-C1/CV power supply units
- MR-J2S / MR-J3 amplifiers (depending on configuration)
Functional Description
The Mitsubishi HC103T is a high-performance AC servo motor designed for dynamic and precise positioning.
Key features:
- Compact size with high power density
- Equipped with an OSA104S2 absolute encoder (1M ppr)
- Suitable for high-accuracy motion control tasks
- Reliable in continuous duty operation
- Designed for easy integration with Mitsubishi CNC and servo drive systems
Alarms & Troubleshooting
| Code | Description | Typical Cause | Measure / Solution |
|---|
| AL.01 | Overcurrent | Motor short circuit, faulty IGBTs, winding fault | Check motor & drive, measure insulation |
| AL.02 | Overvoltage | Power supply spikes, insufficient filtering | Inspect power supply, install filters |
| AL.04 | Overheating (Drive) | Blocked cooling, defective fan | Check/replace fan, improve cooling |
| AL.05 | Motor overheating | Overload, insufficient cooling | Inspect load, improve motor cooling |
| AL.07 | Encoder signal error | Broken cable, oil in encoder, OSA104S2 defect | Check cables & connectors, clean/replace encoder |
| AL.13 | Motor ground fault | Insulation fault in motor winding | Perform insulation test, repair motor |
| AL.15 | Overload (Drive or Motor) | Axis permanently overloaded | Check mechanical load, adjust parameters |
| AL.19 | Overspeed | Parameter error, load uncoupled | Verify parameters, inspect load |
| AL.30 | Excessive position deviation | Encoder fault, mechanical jamming | Check encoder, free mechanical axis |
| AL.51 | Encoder–Drive communication failure | Loose connector, broken cable, signal disturbance | Inspect cable/connector, realign encoder |