12.06.2026 by Viktor Siebert

Introduction: Unexpected Machine Downtime on a Feeler FV-800A.

A few weeks ago, a customer from Sweden contacted us regarding a fault on a Feeler FV-800A machining center equipped with a Mitsubishi Meldas 520AM control system.

The machine could no longer be started. During startup, the following message appeared:

SO 1 Servo Alarm: PR0030

Based on the customer’s initial analysis, everything indicated a fault on the Y-axis. The affected unit was a Mitsubishi MDS-A-SVJ-10 Servo Drive Unit.

What made this case particularly interesting was the customer’s note that we had successfully helped with the repair of a Hitachi lathe approximately 13 years ago and that machine is still operating reliably today.

The MDS-A-SVJ-10 was then shipped to our workshop in Bensheim for inspection.

Initial Diagnosis

During the first power-up, it became immediately apparent that the unit could still be energized, however a strong smell of burnt electronics was noticeable.

After opening the servo amplifier, the visual inspection immediately revealed severe damage in the power supply section.

The following abnormalities were identified:

• Burnt components on the power supply board

• Thermal discoloration in the voltage supply area

• Damaged PCB traces

• Aging-related wear on several electronic components

• Increased thermal stress caused by many years of operation

The damage was so extensive that a component-level repair was no longer economical or reliable in the long term.

Actual Root Cause

The detailed analysis revealed the following causes:

• Failure of multiple components in the internal power supply section

• Secondary damage caused by thermal overload

• Unstable internal supply voltages within the servo drive

• Damage to the power supply board across multiple circuit sections

• High risk of additional failures if only individual components were replaced

In this case, the power supply board was beyond repair and had to be replaced completely.

Repair Measures

The following work was carried out during the repair:

• Complete disassembly of the unit

• Cleaning of all assemblies

• Removal of dust and contamination

• Replacement of the damaged power supply board

• Inspection of the RJ711C control board

• Inspection of the RJ722B-1 / BN634A649G51 power board

• Verification of all supply voltages

• Inspection of communication interfaces

• Functional testing of all protection circuits

• Load testing on our test bench

• Extended operational testing under realistic conditions

Final Testing and Return Shipment

After completion of the repair, the MDS-A-SVJ-10 Servo Drive Unit was tested for several hours on our test bench.

All supply voltages remained stable.

Communication with the CNC control operated correctly.

All protection functions responded according to Mitsubishi specifications.

After successfully completing all final tests, the unit was approved for return shipment.

To mentioned Mitsubishi Drive: Mitsubishi Servo Drive Unit MDS-A-SVJ-10

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

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Technical Specifications

Parameter	Value
Manufacturer	Mitsubishi Electric
Model	MDS-A-SVJ-10
Device Type	Servo Drive Unit
Supply Voltage	3AC 200–230 V
Frequency	50/60 Hz
Input Current	4.3 A
Output Current	8.8 A
Software Version	BND511W000D1
Hardware Version	F
Production Date	06/1997
Manual	BNP-B2057 Servo Maintenance and Adjustment Manual
Axes	Single Axis

Environmental Conditions

Parameter	Value
Operating Temperature	0 to 55 °C
Storage Temperature	-20 to 65 °C
Operating Humidity	40 to 90 % RH
Shock Resistance	3 G
Vibration Resistance	0.6 G
Installation Location	Electrical Cabinet
Cooling	Natural Convection

Compatible Motors

According to the Mitsubishi manual, the MDS-A-SVJ-10 is compatible with various Mitsubishi HA servo motors of that generation.

Typical combinations include:

Motor Series	Power Range
HA-FE Series	50 W to 450 W
HA Series	Up to 1000 W
HA40N
HA43N
HA80N
HA100N

Components

Assembly	Designation	Function
Control Board	RJ711C	Control and Communication
Power Board	RJ722B-1 / BN634A649G51	Power Control
Power Supply Board	RJ722	Internal Voltage Supply
Power Section	Mitsubishi Power Stage	Motor Drive Circuit
Heat Sink	Integrated	Heat Dissipation

Functional Description

The Mitsubishi MDS-A-SVJ-10 belongs to the early MDS-A-SVJ servo amplifier series and is responsible for the precise control of Mitsubishi AC servo motors.

The device performs the following functions:

• Current control

• Speed control

• Position control

• Communication with the CNC control

• Monitoring of motor currents

• Monitoring of supply voltages

• Protection against overcurrent, overvoltage and overload conditions

Feedback is provided by high-resolution motor encoders, enabling precise positioning of machine axes.

Alarm and Troubleshooting Table

Alarm	Fault Name	Description	Reset	Corrective Action
12	Memory Error	Memory fault on control board	AR	Check board
13	Software Processing Error	Software fault	PR	Check electronics
17	A/D Converter Error	Current measurement fault	PR	Check drive
18	Initial Communication Error	Encoder communication fault	PR	Check encoder
22	Detector Data Error	Invalid encoder data	AR	Check encoder
23	Excessive Speed Error	Excessive speed deviation	NR	Check control loop
24	Grounding	Ground fault in motor wiring	PR	Check motor and cables
30	Over Regeneration	Excessive regenerative energy	PR	Check braking resistor
31	Overspeed	Motor speed exceeded limit	PR	Check parameters
32	Power Module Overcurrent	Power section overcurrent	PR	Check power stage
33	Overvoltage	Excessive DC bus voltage	PR	Check supply voltage
46	Motor Overheat	Motor overheating	NR	Check motor
50	Overload 1	Motor or drive overload	NR	Reduce load
52	Excessive Error 1	Excessive position deviation	NR	Check control loop

Preventive Measures for Customers

Action	Recommendation
Clean electrical cabinet	At least once per year
Inspect power supply quality	Annually
Check connectors	Annually
Keep ventilation paths clean	Regularly
Inspect capacitors	Every 8 to 10 years
Inspect power supply section	During every maintenance interval
Perform thermal imaging inspections	Preventively

Conclusion

This repair case clearly demonstrates that older Mitsubishi MDS-A-SVJ-10 Servo Drives often fail not because of the power stage itself, but due to failures within the internal power supply section. In this case, the root cause was identified quickly through smell and visual inspection. By replacing the damaged power supply board, thoroughly inspecting all assemblies and carrying out extensive test bench verification, the servo drive was successfully restored and is now ready for many more years of reliable operation.