18.06.2025 by Viktor Siebert

A long-standing machine operator contacted us with a persistent issue: one of the three Omron servo drives (R88D-UT24V) installed in his CNC machine was frequently displaying Alarm A.10 – Overcurrent.

Some days the error occurred multiple times, other times the machine would run flawlessly for weeks. However, in recent months, the failures had become increasingly frequent.

An Alarm That Halted Production

Each time Alarm A.10 occurred, it meant: a complete machine reboot, re-homing of axes, re-alignment of workpieces – and a loss of valuable production time. In many cases, the workpiece was damaged beyond recovery and had to be discarded. This started impacting overall productivity and quality control.

Suspecting the Motor – An Expensive Misjudgment

The customer initially suspected the servo motor to be the issue. A replacement motor was ordered and installed at a cost of nearly €3,000 – but the problem persisted. The A.10 alarm continued to appear.

Used Units: A Risky and Costly Gamble

As the machine manufacturer no longer supplied replacement drives, the only option seemed to be purchasing a used unit. But this introduced several new concerns. The drive’s parameter configuration was complex, and replacing it would require on-site service by the machine manufacturer at a cost of nearly €1,000 per day – with no guarantee of success.

Although used units were available on the market, their condition was uncertain. In many cases, the same A.10 overcurrent issue may already be present or may occur soon due to component aging.

The Right Decision: Repair Instead of Guesswork

That’s when the customer reached out to us – and made the right choice.

• We are very familiar with Alarm A.10.
• It is a typical aging-related issue that occurs in nearly all R88D-UT24V units after several years of use.
• Most used devices available online are already affected or will be soon, as the internal components degrade over time.

Our Solution: Targeted Repair with Long-Term Reliability

This error has been documented in our repair program for years. We know exactly which components need to be replaced to permanently eliminate the issue.

Our added value:

• We always extract and back up parameters before any repair, even in case of total device failure.
• If a device swap is eventually necessary, we will transfer parameters to the new unit free of charge.
• We have had zero complaints or returns from customers for this repair type.

Fast Repair – Reliable Operation

We completed the repair within just four working days. Since reinstalling the unit, the machine has been running without a single error.

Impressed by the result, the customer has already decided to send us the remaining two servo drives for preventative refurbishment – a smart move to avoid future downtime.

Refurbishment Process for Omron Servo Drive (R88D-UT24V)

Our standard procedures:

1. Incoming inspection
   • Visual check, functional test, error analysis (especially Alarm A.10)
2. Parameter backup
   • Reading and securing customer parameter data
3. Disassembly of the unit
   • Opening the housing, removing dust, residue, corrosion
4. PCB inspection
   • Electrical and visual diagnostics of all boards
5. Replacement of power semiconductors
   • IGBT modules, diodes, driver ICs
6. Renewal of age-sensitive components
   • Electrolytic capacitors, gate drivers, safety components
7. Cleaning and re-coating (if necessary)
   • Especially in cases of oil contamination or harsh environments
8. Full-load testing on test bench
   • Including real motor simulation
9. Simulation of fault conditions
   • To verify proper protection circuit behavior
10. Rewriting parameters (if needed)
    • To restore original operation
11. Safety & insulation testing
    • Including high-voltage and PE ground tests
12. Documentation and shipping
    • With detailed report and optional parameter copy for the customer

Conclusion: Repair Saves Time, Money and Stress

Alarm A.10 is more than a minor fault – it poses a real risk to production. Buying used drives may appear convenient but often brings the same problems back into the system. Targeted repair by a specialist is the smarter, safer path forward.

Additional Information – Omron Servopack

Omron Servopack R88D-UT24V

For further details on our Omron repair services, please visit here.

📞 Please feel free to contact us if you have any questions regarding your Omron drive technology. Our experienced team is always available to assist you.

Device Data

Model	R88D-UT24V
AC Input Voltage	200–230 VAC (permissible range: 170 to 253 V)
AC Input Frequency	50/60 Hz
AC Input Phases	3 Phases (Main circuit) / 1 Phase (Control circuit)
AC Input Current	8.0 A
AC Output Voltage	0–230 V
AC Output Phases	3 Phases
AC Output Rated Current	7.0 A
Continuous Output Current (0-P)	8.6 A
Momentary Maximum Output Current (0-P)	24 A
Power (KW/HP)	0.85 kW (1.14 HP)
Applicable Servomotor Wattage	1.0 kW
Weight	approx. 4.0 kg
Heating Value (Main Circuit)	55 W
Heating Value (Control Circuit)	20 W
Protective Structure	Built into panel.
Insulation Resistance	Min. 1 MΩ (at 500 VDC) between power line and case
Dielectric Strength	1,500 VAC for 1 minute between power line and case

Alarm Messages and Troubleshooting

Alarm Display	Error Description	Probable Cause(s)	Solution / Countermeasures
A.00	Absolute data error	Malfunction of the absolute encoder. Incorrect wiring of the absolute encoder.	Turn ON SEN signal again. Execute setup for absolute encoder again. Correct the wiring.
A.01	Parameter corruption	Internal memory error when turning power on.	Replace Servo Driver.
A.02	Parameter setting error	A parameter was set to a value outside of the setting range. Control board defective.	Correct the parameter setting. If unsuccessful, replace the Servo Driver.
A.10	Overcurrent	Short-circuit or grounding of the servomotor power line. Incorrect U/V/W wiring. Servomotor coils damaged. Main transistor module error.	Check wiring for short-circuit/grounding and correct it. Measure the motor’s insulation resistance, replace motor if necessary. Measure winding resistance. Replace Servo Driver.
A.20	Regeneration error	Regeneration circuit damaged due to excessive regenerative energy.	Replace Servo Driver.
A.30	Deviation counter over	Mechanical lock is in effect. Gain is insufficient. Load is too large. Acceleration is too sudden. Motor or encoder cable malfunction.	Remove mechanical lock. Adjust the gain. Lighten the load or select another servomotor. Lengthen the acceleration time. Correct the wiring.
A.40	Overvoltage / Undervoltage	The main-circuit power supply voltage is outside of the allowable range (170 to 253 VAC). The load inertia is too large.	Check and correct the power supply voltage. Lengthen the deceleration time. Select another servomotor. For vertical axis, add a counterbalance or reduce speed.
A.50	Overspeed	The rotation speed exceeded 4,950 r/min, often due to overshooting. Encoder is wired incorrectly.	Adjust the gain. Lower the maximum speed of the command. Correct the wiring.
A.71 / A.72	Overload	Operating at more than 120% or 135% of the rated torque. Mechanical lock. Incorrect wiring. Load is too large. Power supply voltage has dropped.	Eliminate the cause of the overload (e.g., lighten the load, lengthen acceleration time). Check wiring. Check power supply voltage and raise it. Adjust the gain.
A.80	Encoder error [Absolute]	Absolute encoder faulty wiring or poor contact. Pulse counter malfunction.	Correct the wiring. Turn OFF the SEN signal, reset the alarm, then turn ON the SEN signal again.
A.86	Overheating (heat sink)	The ambient temperature for the Servo Driver is higher than 55°C. The load torque is too high.	Bring the ambient temperature down to 55°C or lower. Lighten the load, lengthen the acceleration time, or select another servomotor.
A.C0	Command input reading error	Malfunctioning of the command input reading area.	Reset and then run again. If the error persists, replace the Servo Driver.
A.C1	Runaway detected	Incorrect wiring of encoder or servomotor power lines.	Correct the wiring.
A.C2	Phase error detected	Incorrect wiring of encoder lines. Faulty connector contact. Incorrect setting on bit E of parameter Cn-01.	Correct the wiring. Insert connectors correctly. Check and correct parameter setting for encoder type (incremental/absolute).
A.C3	Encoder A/B phase disconnection	Encoder lines disconnected or short-circuited. Faulty connector contact. Incorrect setting on bit E of parameter Cn-01.	Correct any disconnected lines. Insert connectors correctly. Check wiring. Check parameter setting for encoder type.
A.C4	Encoder S phase disconnection	Encoder S (Z) phase disconnected or short-circuited. Incorrect wiring.	Correct any disconnected lines. Insert connectors correctly. Check wiring.
A.F1	Missing phase detected	Main-circuit power supply missing a phase or a line is disconnected.	Check the main-circuit power supply wiring.
CPF00 / CPF01	Parameter Unit transmission error	Internal element is malfunctioning (communication between driver and parameter unit).	Reset and then run again. If the error persists, replace the Servo Driver.