31.05.2026 by Viktor Siebert
Repair of a Yaskawa Juspeed-F S300 CIMR-08CS3-2024 Frequency Inverter with Sporadic Restarts in an Industrial Production System
A Subtle Fault with Major Consequences.
A customer from the machine building industry reported a Yaskawa Juspeed-F S300 frequency inverter, model CIMR-08CS3-2024, which repeatedly shut down unexpectedly during operation and then restarted automatically.
The fault was particularly difficult to identify. The machine sometimes operated for hours without any issues before the inverter suddenly stopped. After a few seconds the unit restarted itself, making root cause analysis extremely challenging. Sporadic faults of this kind often lead to unplanned machine interruptions, production losses and lengthy troubleshooting efforts.
After the inverter arrived in our workshop, a systematic analysis was started.
Initial Diagnosis
During the incoming inspection it became apparent that the inverter belonged to one of the earlier generations of the Yaskawa Juspeed-F series.
Nameplate data:
| Parameter | Value |
|---|
| Manufacturer | Yaskawa / Y-E Drive Corporation |
| Model | CIMR-08CS3-2024 |
| Series | Juspeed-F S300 |
| Input Voltage | 180–242 V AC / 180–253 V AC |
| Frequency | 50/60 Hz |
| Input Phases | 3 |
| Input Current | 6.6 A |
| Output Voltage | 180–253 V AC |
| Output Phases | 3 |
| Output Current | 4.5 A |
| Motor Power | 0.75 kW (1 HP) |
The first measurements confirmed the customer’s description. The internal power supply operated unstably. Under load conditions the supply voltage occasionally collapsed, causing the control electronics to perform a complete restart.
Actual Root Cause
The detailed analysis revealed several interconnected faults.
Detected defects:
• Failure in the power stage
• Excessive load on the internal power supply
• Unstable supply voltage to the control board
• Age-related stress of critical assemblies
• Thermal aging caused by long-term operation
The actual root cause was located in the power stage. Internal defects caused increased current consumption, continuously overloading the internal power supply.
The result:
• Voltage drops within the control circuit
• Automatic resets of the electronics
• Irregular restarts
• Sporadic machine downtime
This type of fault is common in older frequency inverters because the power section and control power supply are closely linked.
Repair Measures
Following diagnosis, a complete overhaul was carried out.
Work performed:
• Removal and inspection of the power board
• Repair of the defective power stage
• Inspection of control board CIMR-08CS3-2024 / W30147-2
• Inspection of power board CIMR-08S3 / W30023-1
• Verification of the internal power supply
• Replacement of age-sensitive components
• Cleaning of all circuit boards
• Removal of dust and contamination
• Re-soldering of stressed electrical connections
• Electrical safety inspection
• Long-term load testing
According to the available assembly information, the inverter consists of the following main assemblies:
| Assembly | Designation |
|---|
| Control Board | CIMR-08CS3-2024 / W30147-2 |
| Power Board | CIMR-08S3 / W30023-1 |
| Power Section | Integrated power stage |
Final Testing and Functional Verification
After completion of all repairs, the inverter was tested on our in-house test bench.
The following parameters were verified:
• Mains voltage behavior
• Load changes
• Continuous operation
• Thermal behavior
• Restart behavior
• Output voltages
• Motor operation under load
During the extended test period, no further voltage drops or resets occurred. The inverter operated reliably and was subsequently prepared for return shipment.
Customer Feedback
“The machine is running reliably again. The unexpected restarts have completely disappeared. The detailed fault analysis was especially valuable because the issue had not been clearly identified for a long time.”
Information about the mentioned Servopack and Servomotor:
More information about our Yaskawa repairs can be found here.
Technical Specifications
| Parameter | Value |
|---|
| Model | CIMR-08CS3-2024 |
| Series | Juspeed-F S300 |
| Manufacturer | Yaskawa |
| Input Voltage | 180–242 V AC / 180–253 V AC |
| Frequency | 50/60 Hz |
| Input Phases | 3 |
| Input Current | 6.6 A |
| Output Voltage | 180–253 V AC |
| Output Phases | 3 |
| Output Current | 4.5 A |
| Power | 0.75 kW (1 HP) |
| Control Method | V/f Frequency Inverter |
| Cooling | Air cooled |
Operating Conditions
| Parameter | Value |
|---|
| Ambient Temperature | Depending on installation conditions |
| Cooling | Free air circulation required |
| Humidity | Dry industrial environment recommended |
| Installation Location | Electrical cabinet |
| Dust Protection | Recommended |
| Oil Mist Protection | Recommended |
Integration with Other Equipment
Typical applications:
• Machine tools
• Conveyor systems
• Production machinery
• Variable speed machinery
• Pumps
• Fans
• Auxiliary drives
Functional Description
The Yaskawa Juspeed-F S300 is designed for speed control of three-phase AC motors.
The output frequency is generated electronically and supplied to the motor. This allows continuous and precise speed control.
The inverter additionally monitors:
• Overcurrent
• Overload
• Overtemperature
• Undervoltage
• Overvoltage
• Ground faults
• Internal electronic communication faults
If a fault occurs, the corresponding protective function is activated. Fault indication is performed through the inverter status LED. Alarm types and blink codes are described in the service manual.
Alarm and Fault Codes
The Juspeed-F series uses blink codes of the white fault LED. The number of flashes indicates the fault type.
| Blink Code | Fault | Meaning | Corrective Action |
|---|
| 1 Flash | Motor Burnout Protection | Motor overload or overheating | Reduce load, check cooling |
| 2 Flashes | Instantaneous Overcurrent Protection | Short circuit or overcurrent | Check motor and wiring |
| 3 Flashes | Regenerative Overvoltage Protection | Excessive regenerative voltage | Check braking conditions |
| 4 Flashes | Undervoltage Protection | Supply voltage too low | Check mains supply |
| 5 Flashes | Inverter Ground Fault Alarm | Ground fault or defective power stage | Check output circuit and power stage |
| 6 Flashes | Noise Alarm | Electromagnetic interference detected | Check wiring and shielding |
The blink codes originate from the Juspeed-F fault indication table.
Preventive Measures for Operators
For older Yaskawa Juspeed-F inverters we recommend:
• Regular cleaning of cooling areas
• Inspection of ventilation paths
• Verification of output currents
• Monitoring of power quality
• Inspection of terminal connections
• Preventive overhaul after many years of operation
• Early investigation of sporadic restart symptoms
Many failures in this generation of frequency inverters do not occur suddenly but develop gradually over months or years.
Conclusion
The Yaskawa Juspeed-F S300 CIMR-08CS3-2024 showed a typical fault pattern found in aging frequency inverters: sporadic restarts caused by a defective power stage and the resulting overload of the internal power supply.
By repairing the power section, inspecting all assemblies and performing comprehensive load testing, the inverter was successfully restored to full operational condition. The customer’s machine is once again running reliably and the original drive could continue to be used without any modifications.