28.02.2026 by Viktor Siebert

Initial situation and fault description

A Yaskawa Servopack CACR-SR30SB1BFY100 was sent in for repair. The unit belongs to the proven CACR-SR series, often referred to as VS-800, and is typically used in older CNC machines. The SR30 power class corresponds to approx. 3.0 kW.

According to the technician’s report, the connected motor started briefly during testing, vibrated noticeably and then shut down with alarm A.1. The fault occurred reproducibly during acceleration. In idle condition, no abnormality was visible.

Technically striking was the strong vibration immediately after the enable signal, followed by a rapid shutdown. This behavior indicates an inconsistent current feedback, where the internal overcurrent monitoring responds although there is no mechanical blockage.

Incoming inspection and initial diagnosis

After arrival, a standard visual inspection was carried out. The unit showed age related thermal traces in the power section area. Connectors and terminals were mechanically intact. No obvious broken traces or burn marks.

For the first functional test, the servopack was connected to a test bench with three phase supply approx. 3 x 230 V AC. Before opening the unit or disconnecting connectors, it was disconnected from power, secured against reconnection, the discharge time of the DC link capacitors was observed and absence of voltage was verified.

During the start attempt with reference signal, the motor started briefly but showed clear torque oscillation. Within a few hundred milliseconds, fault A.1 appeared, which in this series indicates an overcurrent condition. Shutdown was performed dynamically via the internal protection logic.

Initial measurements showed that the output currents were asymmetrical and not plausible relative to the load. The current indication in the green measuring circuit deviated significantly from the actual phase current measured with an oscilloscope.

Technical analysis

The CACR-SR series operates with a hybrid analog and digital control structure. Current control is based on internal phase current measurement used as the control variable for pulse width modulation. If a limit value is exceeded or appears to be exceeded, protection function A.1 is triggered.

In this case, the internal current sensor delivered incorrect measured values. The cause was a known weak point of this series in the current sensing section. Due to aging and thermal stress, measurement characteristics drift. The result is incorrect feedback to the current control loop.

Cause effect chain:

Aging of the current sensing component leads to distorted current feedback.
The control interprets this as overcurrent.
The protection logic triggers alarm A.1.
The motor is dynamically shut down.

Additionally, the power stage showed clear signs of wear. The drive stages of the power section exhibited thermal pre damage. Isolated signal drivers in the control section were also affected. This led to unstable pulse modulation, further intensifying the vibration behavior.

This combination of faulty current measurement and worn power stage explains the observed startup behavior.

Repair measures and refurbishment

The repair was carried out in several steps.

First, the complete power stage was overhauled. Heavily stressed power modules were replaced. The control boards with isolated signal transmission were fully renewed.

The faulty current sensor was replaced by a revised version. Afterwards, the current feedback was calibrated to nominal current approx. 26 A according to the SR30 power class.

In addition, the following preventive measures were performed:

• Replacement of thermally stressed heatsink connections
• Cleaning of cooling channels and fan unit
• Inspection of connectors 1CN and 2CN
• Verification of encoder signal quality
• Checking DC link capacitors for ESR and capacitance

All work on live components was carried out exclusively by qualified electrical personnel using appropriate measuring equipment and in compliance with applicable safety regulations.

Final functional test

The functional test was performed on the in house test bench.

Supply: 3 x 230 V AC
Motor load: simulated nominal load approx. 3 kW
Speed range: 0 to 2000 rpm

Test procedure:

• Multiple on off cycles tested
• Reference run at low speed approx. 100 rpm
• Medium speed approx. 1000 rpm
• High speed near nominal speed
• Load changes under continuous operation
• Overcurrent protection test
• Thermal monitoring over approx. 120 minutes

The motor started smoothly without vibration. No renewed A.1 triggering. Current draw was symmetrical and within specification. Temperature behavior was normal.

Result: fault free, stable, reproducible.

Conclusion

Alarm A.1 was caused by distorted current feedback combined with a worn power stage. After replacement of the affected assemblies and recalibration, the servopack operates again within specification.

The repair is sustainable because thermally stressed components were also replaced preventively. This significantly increases operational reliability and avoids unplanned downtime.

To mentioned Yaskawa Drive: Yaskawa CACR-SR30SB1BFY100 AC Servopack

More details about our Yaskawa repair services can be found here:
Yaskawa drive Repair by Industrypart

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Technical Specifications

Parameter	Value
Manufacturer	Yaskawa
Device type	Servo Drive
Model designation	CACR-SR30SB1BFY100
Series	CACR-SR
Power	approx. 3.0 kW
Input voltage	3 x 200 to 230 V AC
Output voltage	3 x 0 to approx. 230 V AC PWM
Rated current	approx. 26 A
Control type	Analog speed control
Feedback	Incremental encoder 5000 P/R
Cooling	Integrated fan
Protection class	IP20
Ambient temperature	0 to 55 °C
Mounting	Control cabinet mounting
Origin	Japan
Product status	Discontinued

Operating environment and application

Typical applications are CNC lathes, milling machines and machine tools from the 1980s and 1990s. Often combined with Yaskawa AC servo motors of the M or F series.

The drive is suitable for positioning tasks with analog reference input. The control cabinet environment should be well ventilated. High continuous thermal stress accelerates aging of power components.

Regular inspection of fan operation and DC link voltage is recommended for older systems.

Functional description

The servopack converts the three phase mains voltage into a controlled PWM output voltage for the servo motor. The internal current control is based on measurement of the motor phase current.

Power stage, control and feedback operate in a closed loop. The encoder provides position and speed information. Current feedback protects against overload.

Protection functions include overcurrent, overvoltage, overheating and phase loss. If limit values are exceeded, dynamic shutdown occurs.

These protection mechanisms are safety relevant as they protect power semiconductors and motor from destruction.

Alarm Messages and Troubleshooting

Code	Fault description	Cause	Solution
A.1	Overcurrent	Motor short circuit or faulty current measurement	Check motor, inspect current sensing
1	Overcurrent	Phase short circuit	Check wiring
2	Main circuit fuse	Internal short circuit	Inspect power section
3	Regeneration error	Braking resistor defective	Check resistor
4	Overvoltage	Mains voltage too high	Check mains supply
5	Overspeed	Encoder signal faulty	Check encoder
A	Overload	Mechanical blockage	Check load
B	Heatsink overheat	Fan defective	Check fan
F	Phase loss	Missing phase	Check mains
8	Cooling fault	Insufficient air circulation	Check control cabinet

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Assembly Overview

Assembly	Functional designation	Function	Inspection or repair notes
Power stage	Power section	Motor drive output	Check for thermal stress
Current sensing	Current measurement circuit	Feedback for control loop	Calibrate
Gate drive stage	Drive stage	Switching of power modules	Check signal waveform
DC link	DC bus	Energy buffering	Check capacitance and ESR
Fan unit	Cooling	Heat dissipation	Check rotation speed
Control board	Control electronics	Setpoint actual comparison	Visual inspection