13.07.2025 by Viktor Siebert
Received for Repair: Yaskawa SGMGH-05A2A21 AC Servo Motor
Recently, we received a Yaskawa SGMGH-05A2A21 AC servo motor, a model commonly used in CNC machines and automated axis systems. This unit belongs to the Sigma II series and is equipped with a UTSAH-B17BB absolute encoder. The customer reported issues with position feedback, typical signs of a damaged or aged encoder.
How the SGMGH-05A2A21 Motor Works
The SGMGH-05A2A21 is a brushless AC servo motor rated at 0.45 kW, with a maximum speed of 1500 rpm, and equipped with a 17-bit absolute encoder. This encoder continuously transmits the rotor’s absolute position, even after power loss, thanks to battery-backed memory.
Due to its robust design and precise positional feedback, this motor is often used in machine tools, tool changers, packaging systems, or linear modules. It is typically paired with the SGDH-05AE servo amplifier and operates in position, speed, or torque control mode.
How Our Repair Process Works
Once a motor arrives at our facility, we begin with a structured incoming inspection. This includes:
- Visual check of housing and shaft
- Insulation resistance test
- Shaft and bearing play
- Condition of connectors, seals, and screws
Next, the motor is disassembled into subassemblies: rotor, stator, bearings, encoder. Each component is cleaned, inspected, or replaced as needed. Wear parts such as bearings and shaft seals are always replaced preventively.
Testing and Final Check with Checklist
After reassembly, the motor undergoes a complete electrical function test on our test bench. We connect it to a compatible Yaskawa SGDH-05AE Servopack and run an automated test program, checking:
- Encoder feedback (absolute position accuracy)
- Shaft rotation, current draw, operating noise
- Motor brake (if equipped)
- Temperature performance under load
All procedures are recorded in a digital checklist linked to the repair job. This ensures traceability and quality control, even for future reference or repeat repairs.
Special Case: Encoder Replacement
In this specific case, we replaced the UTSAH-B17BB absolute encoder. This is often necessary with older units where the encoder battery is depleted, or position data is corrupted (for example, Alarm A.84).
One critical point: The new encoder must be precisely programmed to match the motor. This includes resolution, rotation direction, counting logic, and offset values. We carry out this process using special programming tools and software.
Final Result
After passing final inspection, the motor is returned to the customer with a test report and a unique repair label. It can be reinstalled into the machine immediately, with no further calibration required. Thanks to our structured repair process, checklists, and test systems, we ensure that the motor returns in like-new or better condition.
Information about the mentioned Servopack and Servomotor:
More information about our Yaskawa repairs can be found here.
📞 Feel free to contact us if you have any questions regarding your Yaskawa drive technology. Our experie
Device Data (Technical Specifications)
| Parameter | Value |
|---|
| Model | SGMGH-05A2A21 |
| Power Output | 0.45 kW |
| Rated Voltage | 3-phase 200 V |
| Rated Current | 3.8 A |
| Rated Torque | 2.9 Nm |
| Max Speed | 1500 rpm |
| Encoder | UTSAH-B17BB (17-bit absolute encoder) |
| Insulation Class | Class B |
| Protection Rating | IP65 (depending on configuration) |
| Weight | approx. 4.6 kg |
| Manufacturer | YASKAWA Electric JAPAN |
Operating Environment & Integration
- Application: CNC machines, tool changers, gantry systems, packaging, automation axes
- Mounting: horizontal or vertical
- Conditions:
- Temperature: 0–40 °C operating, -20–60 °C storage
- Humidity: 20–80 % RH non-condensing
- No corrosive gases, no water
- Typical Pairing: SGDH-05AE servo amplifier (Sigma II series)
Functional Description
The SGMGH-05A2A21 is a high-precision AC servo motor of the Sigma II series. It includes a 17-bit absolute encoder (UTSAH-B17BB) for accurate and battery-backed position tracking. The motor supports positioning, speed or torque control modes via compatible servo amplifiers. It’s suited for high-end industrial automation tasks with stable torque and precise motion feedback.
Alarms & Troubleshooting
| Alarm Code | ALO1 | ALO2 | ALO3 | Alarm Name | Description / Remedy |
|---|
| A.02 | OFF | OFF | OFF | Parameter Error | EEPROM damaged – reset amplifier, rewrite parameters |
| A.03 | — | — | — | Encoder / Circuit Fault | Check encoder cable and CN2 connector |
| A.10 | ON | OFF | OFF | Overcurrent / Heat Sink Overload | Verify cooling, check for overload |
| A.32 | ON | ON | OFF | Regenerative Overload | External resistor missing or insufficient |
| A.40 | OFF | OFF | ON | Overvoltage | DC bus voltage too high – check power supply |
| A.41 | — | — | — | Undervoltage | Check supply line |
| A.51 | ON | OFF | ON | Overspeed | Check feedback, machine load and PID settings |
| A.71 / A.72 | ON | ON | ON | Motor Overload (short / continuous) | Reduce load, allow motor to cool |
| A.83 | — | — | — | Encoder Battery Low | Replace battery of UTSAH-B17BB encoder |
| A.84 | — | — | — | Encoder Data Error | Invalid absolute data → check encoder, communication, battery. Reset encoder position |
| A.CC | ON | OFF | ON | Multi-Turn Mismatch | Encoder setting (Pn205) must match servo amplifier → reset required |
Main Components
| Component | Description |
|---|
| Stator | 3-phase windings, class B insulation |
| Rotor | Interior-mounted permanent magnets |
| Encoder | UTSAH-B17BB, 17-bit absolute, with battery |
| Housing | Black anodized cast aluminum with ribbed cooling structure |
| Output Shaft | Straight shaft with keyway; optionally with seal or tapped thread |
