Fuji Alpha 5 Servo Drive Fault Codes List

Complete guide to Fuji Alpha 5 (Smart) servo fault codes. Troubleshoot dL1 Battery alarms, Et Encoder trouble, oL Overloads, and use the Alpha 5 PC Loader for diagnostics.

Alpha 5 Fault Codes Reference Table

Below is the complete list of alarm codes. The display typically alternates between the alarm type and the specific code. Use this table to interpret the error.

  Fuji Alpha 5 Servo Drive Fault Codes List

Fuji Alpha 5 Servo Drive Fault Codes List

Fault Code and Meaning Cause and Remedy
oC1, oC2

Overcurrent
The output current of the servo amplifier exceeds the rated value.

oC1: Direct detection by internal transistor.
oC2: Indirect detection with software.
Cause: Wrong servomotor output wiring
Remedy: Correct the wiring of power cables (U, V and W).
Cause: Short circuit or grounding fault in servomotor output wiring
Remedy: Check cables visually or through continuity check and replace the defective cable.
Cause: Servomotor insulation fault
Remedy: Measure the insulation resistance. (Several MΩ or over to ground).
Cause: Failure of servomotor
Remedy: Measure the resistance across cables. (Several Ω between cables).
Cause: Incorrect resistance of regenerative resistor
Remedy: Replace with the regenerative resistor within the rating.
Cause: Current imbalance caused by an encoder fault
Remedy: Replace the servomotor.
Cause: Unconnected grounding cable
Remedy: Connect the grounding cable.
oS

Overspeed
The rotation speed of the servomotor exceeds 1.1 times the maximum speed.
Cause: Wrong servomotor output wiring
Remedy: Correct the wiring of power cables (U, V and W).
Cause: The rotation speed of the servomotor overshoots.
Remedy: Check the speed waveform during acceleration with the PC Loader or similar and take the following countermeasures:
  • Increase PA1_15 (auto tuning gain 1).
  • Increase PA1_37 (acceleration time).
  • Increase PA1_52 (S-curve time constant).
Hu

Overvoltage
The DC voltage inside the servo amplifier exceeds the upper limit.
(Approx over 420 V).
Cause: The source voltage is too high (immediately after power-on).
Remedy:
  • Check if the source voltage is within the specification limits.
  • Insert a reactor if there is a power factor improvement capacitor.
Cause: Unconnected external regenerative resistor or wrong wiring
Remedy:
  • Connect the external regenerative resistor.
  • Correct the wiring of the external regenerative resistor.
Cause: Broken regenerative transistor
Remedy: Replace the servo amplifier.
Et1, Et2

Encoder Trouble
There is a fault in the encoder built in the servomotor.
Et1: Single revolution position detection fault.
Et2: Encoder memory data reading fault.
Cause: Fault in data sent from encoder
Remedy: Use shielded cables to eliminate noise effects.
Cause: Failure of encoder
Remedy: Replace the servomotor.
ct

Circuit Trouble
There is a fault in the source control power voltage inside the servo amplifier. There may be a failure in the internal circuit.
Cause: Failure of servo amplifier
Remedy: Turn the power off then on again. If restoration is not obtained, replace the servo amplifier.
dE

Memory Error
The parameter data stored in the servo amplifier is damaged.
Cause: Failure of stored data
Remedy:
  • Using the PC Loader, read parameters and enter those indicated in red.
  • Initialize parameters.
  • If restoration is not obtained with the actions above, replace the servo amplifier.
Cause: The parameter overwriting frequency has exceeded 100,000 cycles.
Remedy: Replace the servo amplifier. (Store frequently overwritten parameters to RAM).
Fb

Fuse Blown
The fuse in the servo amplifier main circuit is disconnected.
Cause: The fuse is disconnected.
Remedy: Replace the servo amplifier.
Note: Customers are not allowed to replace the fuse. Contact us before turning on the power.
cE

Motor Combination Error
The capacity and model of the servo amplifier do not agree with those of the connected servomotor.
Cause: The capacity and model of the servo amplifier do not agree with those of the servomotor.
Remedy: Check the capacity and model of the servomotor and those of the servo amplifier.
tH

Regenerative Resistor Overheat
The regeneration handling transistor built in the servo amplifier is overheated.
Cause: High source voltage (immediately after power-on)
Remedy:
  • Check if the source voltage is within the specification limits.
  • Insert a reactor if there is a power factor improvement capacitor.
Cause: Too large regeneration power
Remedy:
  • Increase the deceleration time.
  • Decrease the servomotor rotation speed.
  • Increase the dwell and decrease the regeneration frequency.
Ec

Encoder Communication Error
Communications with the internal encoder of the servomotor fails.
Cause: Error in encoder serial communications
Remedy: Check cables visually and through continuity check and correct faults.
Cause: Broken wire or poor contact
Remedy:
  • Check for the broken wire in the encoder cable and correct if broken.
  • Insert ferrite cores.
ctE

Cont (Control signal) Error
There is duplication in allocation of sequence input terminals of the servo amplifier.
Cause: The same input signal is allocated to two or more terminals.
Remedy: Do not specify the same number among CONT signal settings.
oL1, oL2

Overload
oL1: Alarm that detects failures such as a locked shaft instantaneously.
oL2: The effective torque exceeds the allowable limit of the servomotor.
Cause: The servomotor fails to rotate mechanically.
Remedy:
  • Check the wiring of power cables (U, V and W) and correct faults.
  • Check if the brake is active.
Cause: The mechanical system is too heavy against the servomotor capacity.
Remedy:
  • Examine the servomotor capacity, based on the load factor.
  • If rotation speed can be reduced, add a reduction gear.
  • Apply the brake to retain a stopped elevator.
Cause: The acceleration/deceleration frequency and operation frequency are too high.
Remedy: Increase the cycle time and decrease the operation frequency.
Cause: Servo amplifier is damaged.
Remedy: Replace the servo amplifier.
LuP

Main Power Undervoltage
The power supplied to the servo amplifier falls below the minimum specification voltage limit.
Cause: The source voltage drops due to momentary power failure or similar.
Remedy:
  • Check the power supply environment whether momentary power failure is generated or not, and improve the power supply environment.
  • Check and improve the power supply capacity and transformer capacity.
rH1

Internal Regenerative Resistor Overheat

The power consumption of the regenerative resistor built in the servo amplifier exceeds the upper limit. 		Cause:
  • Excessive source voltage (immediately after power-on).
  • Vertical transfer or winding applications where regenerative power cannot be consumed.
  • The regenerative resistor is not connected.

Remedy:
  • Check if the source voltage is within specification limits.
  • Insert a reactor if there is a power factor improvement capacitor.
  • Increase the deceleration time or decrease servomotor rotation speed.
  • Connect an external regenerative resistor.
  • Install a counterweight.
  • Connect correctly and set PA2_65 at 0 or 2.
rH2

External Regenerative Resistor Overheat

The external regenerative resistor overheat signal (normally closed contact signal) has worked (was open). 		Cause:
  • Excessive source voltage (immediately after power-on).
  • Vertical transfer or winding applications where regenerative power cannot be consumed.
  • Wrong wiring of external regenerative resistor overheat signal.

Remedy:
  • Check if the source voltage is within the specification limits.
  • Increase the deceleration time or decrease servomotor rotation speed.
  • Connect an external regenerative resistor.
  • Install a counterweight.
  • Connect wiring correctly.
rH3

Regenerative Transistor Error

The regeneration handling transistor built in the servo amplifier is damaged. 		Cause:
The regenerative transistor is short circuited or damaged.

Remedy:
  • Turn the power off then on again.
  • If the alarm persists, replace the servo amplifier.
  • Note: If this alarm outputs, turn power off immediately to prevent fire.
rH4

Inrush Current Suppression Circuit Trouble

The circuit inside the servo amplifier which suppresses the inrush current generated at power-on may be broken. 		Cause:
  • The servo amplifier is damaged.
  • The ambient temperature exceeds 55°C.
  • The power is frequently supplied (turned on/off too often).

Remedy:
  • Replace the servo amplifier.
  • Keep ambient temperature at 55°C or lower (40°C recommended). Move heat generating bodies away.
  • Reduce the frequency of turning the power on/off (Reference: once a minute or less).
oF

Deviation Overflow

A position deviation amount equivalent to servomotor revolutions specified in PA2_69 is accumulated inside the servo amplifier. 		Cause:
  • Wrong connection of power cables (U, V, W).
  • Servomotor fails to rotate mechanically (brake applied).
  • Low output torque or low gain.
  • Deviation detection width is too small.
  • Acceleration/deceleration is too acute.

Remedy:
  • Check and correct the wiring of power cables.
  • Check if the brake is applied.
  • Increase PA1_27, _28 (torque limit).
  • Increase PA2_69 (deviation detection overflow value).
  • Perform gain adjustment.
  • Increase the acceleration/deceleration time.
AH

Amplifier Overheat

The temperature of the servo amplifier has exceeded the allowable limit. 		Cause:
  • The ambient temperature exceeds 55°C.
  • Effective torque may be exceeding 100% during operation.

Remedy:
  • Reduce the ambient temperature to 55°C or lower.
  • Move heat generating bodies away from the amplifier.
  • Check effective torque using keypad/PC loader (ensure it does not exceed 100%).
EH

Encoder Overheat

The encoder inside the servomotor is overheated exceeding the allowable temperature. 		Cause:
  • Excessive ambient temperature.
  • The effective torque exceeds the rating.

Remedy:
  • Reduce the ambient temperature of the servomotor to 40°C or lower.
  • Remove shields interrupting heat radiation.
  • Increase the cycle time and reduce the operation frequency.
dL1
dL2
dL3

Absolute Data Lost

The absolute data of the encoder is lost. 		Cause:
  • dL1: Battery voltage drop or broken encoder cable.
  • dL2: Multi-turn data fault in encoder.
  • dL3: Detection at power-on after an ET alarm.

Remedy:
  • For dL1: Check for broken wire/wrong wiring. Replace the battery. Note: Warning displayed if voltage is low.
  • For dL2: Perform position preset. If alarm persists, replace servomotor.
  • For dL3: After position preset, dL3 is cleared but ET alarm persists. If ET alarm cannot be cleared, replace servomotor.
AF

Multi-turn Data Over Flow

Rotation of the output shaft of the servomotor exceeds the range between -32766 and 32765. 		Cause:
Excessive servomotor revolutions.

Remedy:
  • Check the servomotor revolutions.
  • Use the PC Loader or take similar measures to check the current position.
iE

Initial Error

The initial position inside the encoder is not established. 		Cause:
  • The encoder is damaged.
  • The power is turned on while the servomotor rotates due to external force.

Remedy:
  • Replace the servomotor.
  • Stop the servomotor and turn the power off then on again.
  • If restoration is not obtained, replace the servomotor.

How to Read Alpha 5 Faults

Diagnosing the Alpha 5 requires checking the physical amplifier display and using the dedicated PC software. Here is the standard procedure:

  • The 7-Segment Display:
    • Normal Operation: Displays the current feedback (Speed, Position, or Torque) or “run”.
    • Alarm State: Flashes the code (e.g., “oL”). Note that some codes are “Warnings” (drive keeps running) while others are “Alarms” (drive stops).
  • Alpha 5 PC Loader: Connect a PC via the USB Mini-B port on the front face.
    • Monitor Mode: View the “Historical Trace” to see the waveform of the motor current just before the alarm. This is critical for diagnosing “Overload” (oL) vs. “Overcurrent” (oc).
    • FFT Analysis: If the machine is vibrating or making noise, use the FFT tool to find the resonant frequency and set the Notch Filter parameters automatically.
  • Life Warning: The Alpha 5 has a predictive function. If the display shows a warning related to fan life or capacitor life, it indicates the internal components are nearing the end of their design cycle (typically 10 years).

Frequently Asked Questions (FAQ)

Q: What is the “dL1 / dL2 / dL3” Battery Alarm?

A: Most Alpha 5 motors use an Absolute Encoder with a backup battery.

  • dL1 (Battery Low): The voltage is low (Warning). Replace the battery immediately while the power is ON to save position data.
  • dL2 (Battery Fail): The battery is dead. Absolute position data is lost. You must replace the battery and perform a “Home Return” calibration.
  • dL3 (Cable Break): The cable connecting the battery box to the amplifier is broken or unplugged.

Q: How do I fix “Et” (Encoder Trouble)?

A: This indicates a communication break between the amplifier and the motor encoder.

  • Connector: Check the rectangular encoder connector on the motor side. It is prone to vibrating loose.
  • Cable Flex: If the motor moves on a gantry, check for a broken wire inside the cable track.
  • Noise: Ensure the encoder cable shield is grounded properly at the amplifier end.

Q: How do I reset the Alpha 5?

A:

  • Input Signal: Toggle the “RST” (Reset) digital input.
  • Keypad: Press the “SET” and “MODE” keys simultaneously (depending on setup).
  • Power Cycle: Turn off Main Power (L1/L2/L3) and Control Power (L1C/L2C).

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