03.12.2025 by Viktor Siebert
Repair of a Yaskawa SGMP-15V316CT (1500 W) with brake failure and overload on SGDB-15ADG
Repair of a Yaskawa SGMP-15V316CT (1.5 kW) with defective holding brake and overload on SGDB-15ADG
The motor was sent in with the customer’s report that even after replacing the servopack the axis immediately triggered an overload condition.
The customer had installed a new Yaskawa SGDB-15ADG servopack because the previous unit had failed. The new servopack powered up correctly, but the axis entered overload directly at enable.
During the first manual inspection, the motor shaft felt unusually stiff.
For a 1.5 kW motor, the shaft must rotate freely when the brake is released.
This behaviour was a clear indication of a brake that did not open.
After opening the brake assembly, the resistance of the MCNB 73Y-04 brake coil was measured.
Instead of the nominal 85 to 110 Ω, the coil showed more than 2 kΩ and partly unstable values.
This is a typical sign of a thermally damaged brake coil.
A coil with such resistance can no longer generate sufficient magnetic force to lift the armature plate.
The brake does not release, and the shaft remains mechanically locked.
This mechanical lock explains the reaction of the servopack.
The SGDB-15ADG tries to accelerate the motor.
Because the rotor cannot move, the current rises instantly.
The servopack activates its protection and reports overload depending on the duration and current curve:
A.70, A.71 or A.72 Overload.
The customer assumed that the servopack was defective, but the servopack reacted exactly as intended.
It protected the motor and the mechanics from further damage.
The brake was completely removed.
The armature showed thermal discoloration and clear marks of temperature stress.
All mechanical parts were cleaned, the motor shaft was polished, the encoder was checked and the internal wiring inspected.
The encoder UTMSH-20ANP showed perfect signal quality during oscilloscope tests.
The sine and cosine curves were clean and symmetrical, confirming that the encoder was not contributing to the overload behaviour.
After installing a new brake unit, the shaft rotated freely again.
The motor was then tested on our Yaskawa servo test bench.
The following test phases were performed:
- low speed operation
- acceleration cycles up to full rated speed
- load changes between 20 and 80 percent
- brake release and emergency stop simulation
- thermal soak test over 30 minutes
The SGDB-15ADG did not show any further overload events during any test.
The brake opened consistently and without delay.
Thermal behaviour remained stable.
The repairs confirmed that the cause of the overload alarms was not the servopack but a defective brake coil.
After replacing the brake and performing a complete mechanical and electrical inspection, the motor operated without issues.
The customer received a fully restored motor together with the test documentation and measurement protocols.
Preventive measures for the customer
- Measure brake coil resistance every 12 months
- Check the mechanical release of the brake
- Avoid long periods of holding torque under brake load
- Clean connectors and terminal box regularly
- Keep ambient temperature below 40 °C
- Clean servopack SGDB-15ADG regularly
- Ensure smooth axis mechanics to reduce brake wear
Conclusion
The SGMP-15V316CT triggered overload alarms on the SGDB-15ADG due to a high resistance and defective brake coil.
Replacing the brake, cleaning all components, verifying the encoder and conducting a complete load and thermal test restored full operational capability.
Information about the mentioned Servopack and Servomotor:
More information about our Yaskawa repairs can be found here.
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Device Data (Technical Specifications)
| Feature | Value |
|---|
| Model | Yaskawa SGMP-15V316CT |
| Power | 1500 W (1.5 kW) |
| Rated current | 7.5 A |
| Rated torque | 4.7 Nm |
| Rated voltage | 200 VAC |
| Rated speed | 3000 rpm |
| Encoder | UTMSH-20ANP, 2048 ppr incremental |
| Brake | MCNB 73Y-04, 24 VDC |
| Brake coil resistance | approx. 85 to 110 Ω (nominal) |
| Manufacturer | Yaskawa Electric Japan |
| Compatible servopack | Yaskawa SGDB-15ADG |
| Protection class | IP44 (typical) |
| Temperature range | 0 to 40 °C recommended |
Application environment and compatible devices
The SGMP-15V316CT is a compact 1.5 kW servo motor from the early Sigma generation, used in:
- CNC lifting axes
- pick and place units
- tool changers of machining centers
- precision linear axes
- automation systems with higher inertia
It operates together with the servopack Yaskawa SGDB-15ADG, 200 V class, designed for 1.5 kW motors.
Functional description
The SGMP-15V316CT delivers 1.5 kW at 3000 rpm and is controlled by the SGDB-15ADG servopack.
Its 2048 ppr incremental encoder provides precise feedback for position and speed control.
The integrated brake MCNB 73Y-04 opens only when supplied with 24 VDC.
If the coil becomes high resistance, the brake does not release and the shaft remains mechanically locked.
This leads directly to the overload alarms on the SGDB-15ADG:
A.70, A.71, A.72 Overload.
Alarm messages and troubleshooting (SGDB series)
| Code | Description | Cause | Solution |
|---|
| A.70 | Overload | Mechanical blockage, brake does not open | Inspect brake |
| A.71 | Momentary overload | Short blockage | Check mechanical movement |
| A.72 | Continuous overload | Permanent overload | Replace brake |
| A.04 | Overcurrent | Current spike due to locked rotor | Inspect mechanics and motor |
| A.20 | Fuse blown | Internal fuse of servopack | Inspect servopack |
| A.40 | Overvoltage | DC bus voltage exceeded limit | Check supply voltage |
| A.81 | Reference error | Unstable input signal | Inspect controller |
| A.82 | Encoder checksum error | Faulty encoder data | Inspect cable and connector |
| A.83 | Battery alarm | For absolute encoder versions | Replace battery |
| CPF01 | Transmission error | Communication issue | Inspect wiring |
Components
| Component | Type | Function | Inspection |
|---|
| Rotor and stator | SGMP-15V316CT | Generates torque | Insulation and winding test |
| Encoder | UTMSH-20ANP | 2048 ppr feedback | Oscilloscope, signal analysis |
| Brake | MCNB 73Y-04 | Holding torque at 24 VDC | Coil resistance, release function |
| Bearings | precision bearings | Smooth rotation | Axial and radial play |
| Terminal box | Yaskawa standard | Power and signal interface | Pins, isolation |
| Housing | aluminium | Cooling and structural support | Cleaning, corrosion check |