LS L7S Fault Codes List

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Troubleshoot your LS Electric L7S standard servo drive with our updated guide. Learn to interpret AL-xx alarm codes, use DriveView 9 for diagnostics, and resolve common motor trips.

L7S Fault Codes Reference Table

Below is the complete list of protective functions and alarm codes for the L7S series. Please refer to this table to match the code on your drive’s display with the specific hardware, electrical, or tuning diagnostic.

LS L7S Fault Codes List

LS L7S Fault Codes List

Fault Code and Meaning Cause and Remedy
AL-10
IPM fault		 Cause:
Over current (H/W).

Remedy:
  • Check drive output incorrect wiring or encoder incorrect wiring.
  • Check Motor ID, Drive ID, and Encoder settings.
  • Determine whether there is a conflict or binding in the equipment.
AL-11
IPM temperature		 Cause:
IPM overheating.

Remedy:
  • Check drive output incorrect wiring, encoder incorrect wiring.
  • Check Motor ID, Drive ID, Encoder settings.
  • Determine whether there is a conflict or binding in the equipment.
AL-14
Over current		 Cause:
Over current (S/W).

Remedy:
  • Check drive output incorrect wiring, encoder incorrect wiring.
  • Check Motor ID, Drive ID, Encoder settings.
  • Determine whether there is a conflict or binding in the equipment.
AL-15
Current Offset		 Cause:
Current offset error.

Remedy:
  • Check if [St-23], [St-24] are more than 10% of the rated current.
  • Replace the drive.
AL-16
Over Current(/CL)		 Cause:
Over current (H/W).

Remedy:
  • Check drive output incorrect wiring, encoder incorrect wiring.
  • Check Motor ID, Drive ID, Encoder settings.
  • Determine whether there is a conflict or binding in the equipment.
AL-21
Continuous overload		 Cause:
Continuous overload.

Remedy:
  • Determine whether there is a conflict or binding in the equipment.
  • Load condition inspection, Brake operation status check.
  • Check drive output incorrect wiring, encoder incorrect wiring.
  • Check Motor ID, Drive ID, Encoder settings.
AL-22
Room Temperature		 Cause:
Drive overheating.

Remedy:
  • Check drive internal temperature [St-19].
  • Check Cooling fan installation and load condition inspection.
AL-23
Regen. Overload		 Cause:
Regenerative overload.

Remedy:
  • Check Input voltage, regeneration braking resistor and wiring.
  • Drive replacement.
AL-24
Motor Cable Open		 Cause:
Motor disconnection.

Remedy:
  • Check Motor wiring.
AL-30
Encoder Comm.		 Cause:
Serial encoder communication error.

Remedy:
  • Check for incorrect wiring of the serial encoder cable.
AL-31
Encoder Cable Open		 Cause:
Encoder cable open.

Remedy:
  • Check whether cable is disconnected.
AL-32
Encoder Data Error		 Cause:
Encoder data error.

Remedy:
  • Check [P0-02] Setting value.
  • Check encoder wiring.
AL-33
Motor Setting Error		 Cause:
Motor ID setting error.

Remedy:
  • Check [P0-00] setting value.
AL-34
Encoder Z PHASE Open		 Cause:
Encoder Z phase disconnection.

Remedy:
  • Check whether cable is disconnected.
AL-35
Low Battery Error		 Cause:
Low Battery Error.

Remedy:
  • Back-up battery low voltage when using absolute encoder: Battery Replacement.
  • Note: After replacing the battery, power is re-applied and origin operation is required. (Applies from S/W Ver 1.28).
AL-36
Preset Error		 Cause:
Encoder initialization.

Remedy:
  • Back-up battery replacement when using absolute encoder.
  • Lack of voltage and first coupling of encoder.
  • Note: After replacing the battery and alarm reset, power is re-applied and origin operation is required.
AL-40
Under Voltage		 Cause:
Low Voltage.

Remedy:
  • Check input voltage.
  • Check power wiring.
AL-41
Over Voltage		 Cause:
Over voltage.

Remedy:
  • Check Input voltage.
  • Check braking resistor damage and wiring.
  • Excessive regenerative operation, check regenerative resistor.
AL-42
RS-T Power Fail		 Cause:
Main power error.

Remedy:
  • Check power supply wiring and power supply.
AL-43
Control Power Fail		 Cause:
Control power error.

Remedy:
  • Check power supply wiring and power supply.
AL-50
Over Speed Limit		 Cause:
Over speed.

Remedy:
  • Check encoder error, encoder setting value, encoder wiring.
  • Check gain setting, motor wiring, motor ID.
  • Check electrical gear ratio, speed command scale.
AL-51
Position Following		 Cause:
Excessive positional error.

Remedy:
  • Check the position command pulse excessive.
  • Check [P4-11] setting value, wiring and limit contact.
  • Check gain setting value, encoder setting, and electrical gear ratio setting.
  • Check equipment restraints and load conditions.
AL-53
Over Pulse CMD		 Cause:
Pulse command frequency error.

Remedy:
  • Check pulse command frequency from upper controller.
  • Check Command pulse type.
AL-54
Speed Deviation		 Cause:
Excessive speed error.

Remedy:
  • Check drive output miswiring, encoder miswiring.
  • Check equipment restraint and load status.
AL-55
Motor Over Run		 Cause:
Runaway motor.

Remedy:
  • Check drive output miswiring, encoder miswiring.
  • Check equipment restraint and load status.
AL-63
Parameter Checksum		 Cause:
Parameter error.

Remedy:
  • Check parameter values.
AL-64
Parameter Range		 Cause:
Parameter range error.

Remedy:
  • Check parameter values.
AL-71
Invalid Factory Setting		 Cause:
Factory setting error.

Remedy:
  • Check parameter values.
AL-72
GPIO Setting		 Cause:
Output setting error.

Remedy:
  • Check parameter values.
W-01
RST_PFAIL		 Cause:
Main power source loss.

Remedy:
  • Main power is not applied when [P0-06] DIGIT2 is set to 1.
W-02
LOW_BATT		 Cause:
Low battery.

Remedy:
  • When applying the absolute value encoder, the output voltage of the encoder backup battery is insufficient.
W-04
OV_TCMD		 Cause:
Excessive torque command.

Remedy:
  • A command exceeding the maximum set torque was input.
W-08
OV_VCMD		 Cause:
Excessive speed command.

Remedy:
  • A command exceeding the maximum set speed was input.
W-10
OV_LOAD		 Cause:
Overload warning.

Remedy:
  • The maximum setting overload [P0-13] setting range has been reached.
W-20
SETUP		 Cause:
Capacity selection.

Remedy:
  • The motor current capacity is greater than the drive current capacity.
W-40
UD_VTG		 Cause:
Low battery warning (DC-link Low Voltage).

Remedy:
  • When [P0-06] DIGIT2 setting is 1, DC-link voltage is less than 190V.
W-80
EMG		 Cause:
EMG Contact.

Remedy:
  • Check I/O wiring and [P2-09] set value.
 

How to Read L7S Faults via DriveView 9

While the on-board LED display is the quickest way to see an alarm, connecting your PC to the L7S via the USB or RS-422 port using DriveView 9 software provides the detailed telemetry required for 2026 maintenance standards.

  • Alarm History Tracking: The L7S stores the last 16 alarms in non-volatile memory. DriveView 9 allows you to view these with precise power-on timestamps, which is essential for determining if AL-41 (Undervoltage) trips are occurring during specific factory load shifts.
  • Real-Time Waveform Monitor: You can graph Torque Command, Actual Speed, and Position Error. This is critical for diagnosing if an AL-40 (Overload) trip is caused by a mechanical jam or an aggressive acceleration curve.
  • I/O Terminal Status: View the real-time state of digital inputs. This helps verify if an external Limit Switch or an Emergency Stop signal is triggering an AL-32 (External Trip).

General Troubleshooting Steps for L7S Servos

Before performing a reset, verify these three critical areas of the L7S servo system:

  1. Check Control Power (L1C, L2C): Many intermittent AL-41 (Undervoltage) trips are caused by unstable control power. Ensure these terminals have a steady supply independent of heavy motor loads.
  2. Encoder Cable Noise (AL-21): For encoder communication errors, ensure the feedback cable is properly shielded and grounded. In 2026, ensure the encoder cable is not running parallel to high-power AC lines to prevent EMI interference.
  3. Regeneration Overload (AL-14): If the drive trips during rapid stops, check the regenerative resistor. Ensure the resistor value in parameter [P0-11] matches the physical hardware installed.

Frequently Asked Questions (FAQ)

Q: What is the difference between AL-10 and AL-40?

A: AL-10 is an “Overcurrent” trip, usually caused by a sudden short circuit or an IPM failure. AL-40 is an “Overload” trip, meaning the motor has been drawing high current for a sustained period, usually due to mechanical friction or being undersized for the load.

Q: How do I reset a fault on the LS L7S?

A: Once the root cause is resolved, you can reset the drive by:

  • Pressing the [SET/RESET] key on the front panel.
  • Activating the digital input assigned as ALMRST (Alarm Reset).
  • Performing a power cycle (Wait for the “Charge” LED to go dark before turning power back on).

Q: Why does my drive show “bb” on the display?

A: bb stands for Base Block. This is a status indicator, not a fault. It means the drive is healthy but the “Servo-ON” (SVON) signal is missing. The motor will not have holding torque until this signal is applied.

Q: What does “AL-24” (Absolute Position Lost) mean?

A: This alarm occurs when using an absolute encoder if the battery backup voltage has failed. You must replace the battery and perform an Absolute Encoder Reset to re-establish the zero-point of your machine axis.

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