Fuji Alpha 7 Servo Drive Fault Codes List

Complete guide to Fuji Electric Alpha 7 (ALPHA7) servo fault codes. Troubleshoot AL.oc1 Overcurrent, AL.Et1 Encoder errors, STO safety trips, and use the Alpha 7 Loader software.

Alpha 7 Fault Codes Reference Table

Below is the complete list of alarm codes. The display typically shows “AL.” followed by the specific code. Use this table to identify the issue.

Fuji Alpha 7 Servo Drive Fault Codes List

Fuji Alpha 7 Servo Drive Fault Codes List

Fault Code and Meaning Cause and Remedy
OC01 / OC02

Overcurrent
(Display: oc 01 / oc 02)

The output current of the servo amplifier exceeds the rated value.
OC01: Direct detection
OC02: Indirect detection 		Cause:
  • Wrong servomotor output wiring.
  • Short circuit or grounding fault in servomotor output wiring.
  • Servomotor insulation fault.
  • Failure of servomotor.
  • Incorrect resistance of braking resistor.
  • Current imbalance caused by an encoder fault.
  • Unconnected grounding cable.

Remedy:
  • Correct the wiring of power cables (U, V and W).
  • Check cables visually or through continuity check and replace the defective cable.
  • Measure the insulation resistance (Several MΩ or over to ground).
  • Measure the resistance across cables (Several Ω between cables).
  • Replace with the braking resistor within the rating.
  • Replace the servomotor.
  • Connect the grounding cable.
oS

Overspeed
(Display: oS)

The rotation speed of the servomotor exceeds 1.1 times the maximum speed. 		Cause:
  • Wrong servomotor output wiring.
  • The rotation speed of the servomotor overshoots.

Remedy:
  • Correct the wiring of power cables (U, V and W).
  • Check the speed waveform during acceleration with the PC Loader. Take the following countermeasures:
    • Increase PA1_37 (acceleration time).
    • Increase PA1_52 (S-curve time constant).
    • Increase PA1_56 (speed loop gain 1).
Lu / cn

Control Power Undervoltage
(Display: Lu cn)

The voltage of the control power supplied to the servo amplifier temporarily drops below the minimum specification limit. 		Cause:
  • The source voltage drops due to momentary power failure or similar.
  • Poor power supply capacity of transformer, etc.

Remedy:
  • Check the power supply environment for momentary power failure and improve the environment.
  • Check and improve the power supply capacity and transformer capacity.
  • Replace the transformer, etc.
Hu

Overvoltage
(Display: Hu)

The DC voltage inside the servo amplifier exceeds the upper limit (approx 420V). 		Cause:
  • The source voltage is too high (immediately after power-on).
  • Unconnected internal regenerative resistor.
  • The regenerative energy is high.
  • Unconnected external braking resistor or wrong wiring.
  • Broken braking transistor.

Remedy:
  • Check if the source voltage is within the specification limits.
  • Insert a reactor if there is a power factor improvement capacitor.
  • Check the short-circuit wire between the RB2 and RB3 terminals.
  • Use an external regenerative resistor.
  • Connect the external braking resistor and correct its wiring.
  • Replace the servo amplifier.
Et01 / Et02

Encoder Trouble
(Display: Et 01 / Et 02)

There is a fault in the encoder built in the servomotor.
Et01: Single revolution position detection fault
Et02: Encoder memory data reading fault 		Cause:
  • Fault in data sent from encoder.
  • Failure of encoder.

Remedy:
  • Use shielded cables to eliminate noise effects.
  • Replace the servomotor.
dE

Memory Error
(Display: dE)

The parameter data stored in the servo amplifier is damaged. 		Cause:
  • Failure of stored data.
  • The parameter overwriting frequency has exceeded 100,000 cycles.
  • The servo-on is turned on without turning the power off and then on after the parameter was initialized.

Remedy:
  • Using the PC Loader, read parameters and enter those indicated in red.
  • Initialize parameters.
  • Turn the power off then on again. If restoration is not obtained, replace the servo amplifier.
  • Replace the servo amplifier (if overwrite limit exceeded).
  • Supply the power again.
cE

Motor Combination Error
(Display: cE)

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.
Ec

Encoder Communication Error
(Display: Ec)

Communications with the internal encoder of the servomotor fails. 		Cause:
  • Interrupted encoder communications.
  • Broken wire or poor contact.
  • Noise interference (route cable near magnetic fields).

Remedy:
  • Check cables visually and through continuity check and correct faults.
  • Check for the broken wire in the encoder cable and correct.
  • Insert ferrite cores.
  • Do not route the encoder cable in a strong magnetic or electric field. Route separately from power lines.
co nt

CONT (control signal) Error
(Display: co nt)

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.
oL 01 / oL 02

Overload
(Instantaneous alarm or Effective torque exceeds limit)		 Cause:
  • The servomotor fails to rotate mechanically.
  • The mechanical system is too heavy against the servomotor capacity.
  • The acceleration/deceleration frequency and operation frequency are too high.
  • Servo amplifier is damaged.

Remedy:
  • Check if the brake is active.
  • 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.
  • Increase the cycle time and decrease the operation frequency.
  • Replace the servo amplifier.
  • If OL02 occurs without damage/wiring issues, examine servomotor capacity.
rH 04

Inrush Current Suppression Circuit Trouble		 Cause:
  • The servo amplifier is damaged.
  • The ambient temperature exceeds 55°C.
  • The power is frequently supplied.

Remedy:
  • Replace the servo amplifier.
  • Keep the ambient temperature 55°C or lower (40°C or below is recommended).
  • Move heat generating bodies near the servo amplifier as far away as possible.
  • Reduce the frequency of turning the power on/off (Reference: once an hour or less).
  • Note: If detected when temp is below 55°C, replace amplifier.
SF tY

Safety function error		 Cause:
  • The [EN1+], [EN2+] terminal input mismatch continued for 50 ms or longer.
  • The function safety module (WSU-ST1) output an alarm.
  • A servo amplifier or function safety module (WSU-ST1) fault occurred.

Remedy:
  • Check for wiring abnormalities such as disconnection or shorting in the [EN1+], [EN2+] terminal wiring.
  • Reduce the [EN1+], [EN2+] terminal input mismatch time to 50 ms or less.
  • Refer to the function safety module (WSU-ST1) User's Manual.
  • Turn power OFF/ON. If not resolved, replace servo amplifier or safety module.
  • Check the function safety module mounting condition.
Lu Po

Main Power Undervoltage		 Cause:
  • The source voltage drops due to momentary power failure or similar.
  • The power is turned on or off intentionally.
  • DC input is under execution.

Remedy:
  • Check the power supply environment (momentary failure) and improve capacity/transformer.
  • Do not turn the power on after the time specified in PA2_68 has elapsed.
  • Set PA2_68 (main power shutoff detection time) at 1000 [ms].
  • If environment is adverse, PA2_67 can be applied to ignore undervoltage detection.
rH 01

Internal Braking Resistor Overheat		 Cause:
  • Excessive source voltage (immediately after power-on).
  • Due to vertical transfer or winding purpose, regenerative power cannot be consumed.

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.
  • Decrease the servomotor rotation speed.
  • Increase the cycle time and decrease the operation frequency.
  • Connect an external braking resistor.
  • Install a counterweight.
rH 02

External Braking Resistor Overheat		 Cause:
  • Excessive source voltage (immediately after power-on).
  • Due to vertical transfer or winding purpose, regenerative power cannot be consumed.
  • Wrong wiring of external braking resistor overheat signal.

Remedy:
  • Check if the source voltage is within the specification limits.
  • Increase the deceleration time.
  • Decrease the servomotor rotation speed.
  • Increase the cycle time and decrease the operation frequency.
  • Connect an external braking resistor or install a counterweight.
  • Connect the wiring correctly.
rH 03

Braking Transistor Error		 Cause:
  • The braking transistor is short circuited or damaged.

Remedy:
  • Turn the power off then on again. If the alarm persists, replace the servo amplifier.
  • Note: If short circuited/damaged, fire may be caused. Turn power off immediately.
oF
Deviation Overflow		 Cause: Wrong connection of power cables; Servomotor mechanically locked; Low output torque; Deviation detection width is small; Amplifier is in P control mode; Low gain; Rapid acceleration/deceleration; External pulse phase mismatch.

Remedy:
  • Check and correct the wiring of power cables (U, V and W).
  • Check if the brake is applied.
  • Increase torque limit values (PA1_27 and 28).
  • Increase the deviation overflow detection value (PA2_69) or External/Motor deviation over detection value (PA4_36).
  • Turn off the P motion signal.
  • Perform gain adjustment.
  • Increase the acceleration/deceleration time.
  • Check the set value of PA4_32 (external pulse phase selection).
AH
Amplifier Overheat		 Cause: The ambient temperature exceeds 55 [°C]; Heat generating bodies are too close.

Remedy:
  • Reduce the ambient temperature to 55 [°C] or lower (40 [°C] recommended).
  • Move heat generating bodies near the servo amplifier as far away as possible.
  • Perform operation at a continuous load factor within 100%.
EH
Encoder Overheat		 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, if there are any.
  • Increase the cycle time and reduce the operation frequency.
dL 01 / dL 02 / dL 03
Absolute Data Lost		 Cause:
dL01: Battery voltage drop, broken cable.
dL02: Multi-turn data fault in encoder.
dL03: Detection at power-on after an Et alarm.

Remedy:
  • dL01: Replace the battery and preset the position. Check if encoder cable is broken.
  • dL02: Perform position preset. If the alarm persists, replace the servomotor.
  • dL03: Perform position preset. If the Et alarm is not canceled, replace the servomotor.
AF
Multi-turn Data Overflow		 Cause: Excessive servomotor revolutions (Output shaft exceeds range between -32766 and +32765).

Remedy:
  • Check the servomotor revolutions.
  • Use the PC Loader or take similar measures to check the current position.
iE
Initial Error		 Cause: The encoder is damaged; Power turned on while the servomotor rotates on 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.
HF
Command Pulse Frequency Error		 Cause: Gear Ratio was changed; The set value of pulse such as electronic gear setting is large.

Remedy:
  • Review the master processing.
  • Set the ratio of pulses to an appropriate setting value.
oL 03
Overload 3 (Output open-phase)		 Cause: The servomotor fails to rotate mechanically.

Remedy:
  • Check the wiring of power cables (U, V and W) and correct faults.
cY
Cycle communication error		 Cause: An error occurred during EtherCAT communication.

Remedy:
  • Check the condition of the communication cable (disconnection, etc.), and fix if necessary.
  • Insert a ferrite core into the communication cable.
  • Adjust the interval between the communication timing and DC timing.
  • Check whether the ESM State is other than OP with servo-on.
 

How to Read Alpha 7 Faults

Diagnosing the Alpha 7 requires understanding the difference between servo amplifier faults and motor feedback errors. Here is the standard procedure for 2026:

  • The 7-Segment Display: The amplifier display scrolls the alarm code.
    • AL.oc1 / oc2: Overcurrent. This is usually a short in the motor cable or a mechanical jam.
    • AL.Et1 / Et2: Encoder Trouble. This indicates a break in the feedback cable or a failed encoder inside the motor.
    • AL.EcF: Safety Function Error. This is unique to the Alpha 7 and indicates a problem with the Safe Torque Off (STO) inputs.
  • Alpha 7 PC Loader Software: Connect your PC via the USB mini-B port on the front of the amplifier.
    • Alarm History: The software stores the last 20 alarms with timestamps and internal drive status (Bus Voltage, Speed, Torque) at the moment of failure.
    • Life Prediction: Use the “Maintenance” tab to check the remaining life of the electrolytic capacitors and the cooling fan.
  • Safety Module (WSU-ST1): If you are using the optional safety module, check the LEDs on the module itself. A flashing “ERR” LED often indicates a wiring mismatch between the dual safety channels.

Frequently Asked Questions (FAQ)

Q: How do I reset the Alpha 7 Servo?

A: You can reset the drive by:

  • Triggering the RST (Reset) input signal (Sequence Input 11).
  • Pressing the “SET/ESC” button on the keypad (if in local mode).
  • Cycling the main Control Power (L1C, L2C).

Q: What does “AL.dL1” (ABS Battery Low) mean?

A: The Alpha 7 motors often use Absolute Encoders that require a battery to remember position when power is off.

  • AL.dL1: Battery voltage is low (Warning). Replace the battery immediately.
  • AL.dL2: Battery voltage is dead. The absolute position data is lost, and the machine will require “Homing” (Return to Origin) after the battery is replaced.

Q: How do I fix “AL.os” (Overspeed)?

A: This means the motor speed exceeded the maximum limit.

  • Tuning: The servo gains might be too high, causing the motor to overshoot and oscillate. Perform “Auto-Tuning” using the PC Loader.
  • Wiring: Check the UVW motor phases. If they are swapped, the motor will run away instantly and trip.

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