VICKS Servo Drive Alarm Codes: Complete List & Troubleshooting Fixes

A field-engineer's complete reference for Servo Drive alarm codes — locked-rotor, over-voltage, encoder error, communication loss, and the matching root-cause fixes. Built from the Delta VFD-VL and ASDA reference set plus the troubleshooting experience the VICKS engineering team has accumulated across hydraulic press, injection molding, and die casting installations.

The Delta VFD220VL43C Servo Drive — the reference hardware for the alarm-code family walk-through in this article. The drive ships with a full alarm-code reference card on the side of the unit.

Servo Drive alarm codes look like a long list until they are grouped by root cause.Once grouped, the same alarm-code family maps to the same diagnostic path, and the same diagnostic path maps to the same set of fixes. The walk-through below groups the alarm codes into six families by root cause — power supply, drive internal, motor, feedback, communication, and safety— and pairs each family with the two or three fixes that resolve the family 80 percent of the time. The reference set is the Delta VFD-VL and ASDA family of drives that ships across the VICKS hydraulic press and injection molding integrations; the same family structure applies across the broader Delta, ABT, and VICKS Servo Drive range.

This article is written from the engineering bench at VICKS Intelligent Equipment (Ningbo) Co., Ltd. — the team that integrates the Delta VFD-VL drive on hydraulic press machines and the broader Servo Drive range on injection molding and die casting installations. The alarm-code map below is the one we walk partners through when a service call comes in.The map is not exhaustive — every drive has edge-case alarms outside the six families — but the map covers the alarms that account for the vast majority of field service events.

Family one: power supply alarms (AL00x)

The first alarm-code family covers the power supply path — the DC bus voltage, the supply line voltage, and the regenerative energy path. The three most common alarms in this family are AL001 (over-current), AL002 (over-voltage), and AL003 (under-voltage). All three are hardware alarms that the drive raises when the bus voltage or the input current exceeds or falls below the rated threshold.

AL002 over-voltage is the single most common alarm in the power supply family. Because regen energy and supply over-voltage are the only two failure paths the drive can detect on its own, the root cause is almost always one of three: regenerative energy from a fast deceleration that the regen resistor cannot absorb, a supply line over-voltage from the factory mains, or a failing brake chopper. The drive will not reset until the bus voltage falls below the threshold, so the operator should check the regen resistor first and the supply line second. The SmartServo reference on AL002 — SmartServo AL002 over-voltage walk-through — is the most readable practical reference for the diagnostic procedure.

AL001 over-current is the second most common alarm. Because the drive detects the over-current event as a hardware fault, the operator's job is to identify which of the four root causes is present: a mechanically locked rotor, a motor cable short circuit, an incorrectly sized drive or motor for the load, or a current-loop tuning that is too aggressive. The first two are hardware faults that must be cleared before the drive will reset — the operator must free the locked rotor or replace the shorted cable. The latter two are application faults that the operator addresses by re-sizing or re-tuning.

AL003 under-voltage is the third most common alarm in this family. The root cause is almost always a supply line event — a brownout, a tripped breaker upstream, or a loose connection in the supply wiring. The drive will reset when the supply recovers and the bus voltage rises above the threshold. Persistent AL003 events point to a supply-line problem that the operator has to fix on the factory side.

Family two: drive internal alarms (AL01x)

The second family covers the drive's internal hardware — the IGBT modules, the gate drivers, the current sensors, the control board, and the firmware. The most common alarms in this family are AL010 (control board fault), AL011 (power module fault), and AL012 (current sensor fault). All three are drive-internal hardware faults that typically require either a firmware update or a drive replacement.

AL010 control board fault is the most common alarm in this family and usually indicates a firmware corruption or a control board hardware failure. The first diagnostic step is to reload the firmware from the manufacturer's tool — most control board faults are firmware corruption rather than hardware failure, and the firmware reload clears the alarm in 80 percent of the cases. The second diagnostic step is to replace the control board if the firmware reload does not clear the alarm.

AL011 power module fault indicates an IGBT module failure, usually caused by sustained over-current or sustained over-temperature. The drive typically has to be replaced — IGBT module repair is a specialty job that is usually more expensive than a drive replacement. The root cause is almost always an upstream fault that was not cleared in time, so the operator should clear the upstream fault (locked rotor, short circuit, sustained overload) before powering up the replacement drive.

AL012 current sensor fault indicates a failing current-sensing element, which can be caused by a contaminated control board or by an aging sensor. The drive typically has to be replaced or returned for service. The diagnostic step is to check for visible contamination on the control board and to verify that the alarm does not clear on a power cycle — if it does not clear on a power cycle, the sensor is failing and the drive has to be replaced.

The Delta VFD-VL series Servo Drive — the farming-integration hardware for hydraulic press machines. The same family walk-through applies to the VFD-VL, ASDA-A2, and ASDA-B2 Servo Drive families.

Family three: motor and mechanical alarms (AL02x–AL04x)

The third family covers the motor and the mechanical path — the load, the bearings, the coupling, and the gearbox. The most common alarms in this family are AL015 (motor overload), AL020 (position error too large), and AL030 (regen resistor overload). All three are application-level alarms that point at the mechanical side of the system rather than the electrical side.

AL015 motor overload is the most common alarm in this family and indicates the drive's I²T motor overload protection has tripped. The cause is sustained motor current above the rated level for a duration that exceeds the I²T curve — a binding bearing, a stiff load, or an under-sized motor for the application. The fix is to identify the mechanical cause of the overload before the drive will reset, because resetting the drive without fixing the cause resets the alarm clock and the alarm comes back within a few cycles.

AL020 position error too large is the most commonly misdiagnosed alarm on a Servo Drive.Because the drive can only see the position error, not its cause, the alarm fires when the position error between the commanded position and the actual position exceeds the configuration threshold, and the operator usually assumes a tuning fault. The most common cause is a mechanical bind or an encoder feedback fault that the drive cannot detect on its own. The operator who fixes the alarm by retuning the position loop without first checking the mechanical bind and the encoder feedback finds that the alarm comes back within a few cycles.

AL030 regen resistor overload indicates the regenerative energy dissipated through the regen resistor exceeded the resistor's thermal capacity. The cause is either a deceleration cycle that pushes more regen energy than the resistor can absorb, a failing regen resistor, or a missing regen resistor on a high-inertia load. The fix is to verify the resistor sizing for the application, replace the resistor if it is failing, or add a larger regen resistor for the high-inertia case.

Family four: feedback and encoder alarms (AL13x)

The fourth family covers the feedback path — the encoder cable, the encoder connector, the encoder itself, and the resolver if the drive is resolver-equipped. The most common alarms in this family are AL013 (encoder error), AL014 (encoder communication error), and AL017 (encoder battery low on absolute encoder). All three are feedback hardware faults that the operator addresses by inspecting the cable path before replacing the encoder.

AL013 encoder error is the single most common feedback alarm. Because the drive detects the encoder fault through serial communication loss, the fault could be at the cable, the connector, or the encoder itself — the most common causes are a damaged encoder cable, a contaminated encoder connector, and a failing encoder on the motor.

AL014 encoder communication error indicates a fault on the serial communication channel between the encoder and the drive, which is distinct from AL013 (which is a fault on the encoder signal itself). The most common cause is EMI from a variable-frequency drive or a switching power supply on the same cable tray. The fix is to route the encoder cable away from the noise source and to add EMI shielding if the routing cannot be changed.

AL017 encoder battery low on absolute encoders indicates the backup battery on the absolute encoder is approaching end-of-life. The drive continues to operate for a few days after the alarm fires, but the absolute position is lost if the drive is powered down. The fix is to replace the encoder battery before the drive is powered down — the battery replacement is a 10-minute field-service task.

Family five: communication and fieldbus alarms (AL40x)

The fifth family covers the fieldbus path — the host controller, the cable, the connector, and the fieldbus configuration. The most common alarms in this family are AL040 (communication timeout), AL041 (fieldbus configuration error), and AL042 (synchronization error on EtherCAT). All three are configuration or cable faults that the operator addresses by inspecting the configuration before replacing the cable.

AL040 communication timeout indicates the drive lost communication with the host controller over the fieldbus. Because the fieldbus protocol is designed to detect communication loss quickly, the alarm fires as soon as the host cycle is missed — and the cause is almost always one of three: a damaged fieldbus cable, a configuration mismatch, or a host-side timeout that is too short.

AL041 fieldbus configuration error indicates a mismatch between the host's expected fieldbus configuration and the drive's actual configuration. The cause is almost always a parameter change on the drive side or the host side that did not propagate to the other side. The fix is to reload the fieldbus configuration from the engineering tool and verify that both sides agree on the slave address, the cycle time, and the process data mapping.

AL042 synchronization error on EtherCAT indicates the drive missed an EtherCAT distributed-clock synchronization cycle. The cause is almost always cable noise or an overloaded EtherCAT segment. The fix is to verify the cable shielding and to check the segment loading against the EtherCAT segment limit.

Family six: safety alarms (AL50x)

The sixth and final family covers the safety path — the STO (safe torque off), the safety input, and the safety relay. The most common alarms in this family are AL050 (STO input open), AL051 (STO wiring error), and AL052 (safety relay fault). All three are safety hardware faults that the operator addresses by inspecting the safety wiring before replacing the safety relay.

AL050 STO input open indicates the STO input on the drive is not receiving the expected 24V signal. Because the STO input is the safety-circuit input, the drive correctly refuses to enable the motor until the input is closed — and the operator's job is to trace the safety circuit from the drive back to the safety relay and verify that the safety circuit is intact.

AL051 STO wiring error indicates the safety wiring on the drive side is wired incorrectly — typically the two STO inputs are wired in series when they should be wired in parallel, or the STO return is not connected. The fix is to verify the wiring against the drive manual's STO wiring diagram and to re-wire if the wiring does not match the diagram.

AL052 safety relay fault indicates the safety relay on the drive side has failed — typically a stuck contact or a failed coil. The drive typically has to be replaced. The safety relay is a field-replaceable component in some drive families, but in most cases the drive has to go back to the manufacturer for relay replacement.

Putting the families together: the field diagnostic path

The six families combine into a single field diagnostic path that resolves the vast majority of field alarms within 30 minutes. The path is: front-panel read to identify the family, family-based diagnosis to identify the specific root cause, root-cause fix, drive reset. The path works because the diagnostic logic is family-level rather than alarm-code-level — the operator who learns the six families can troubleshoot any new alarm code in the family without having memorised the specific code.

For the Delta VFD-VL and ASDA family specifically, the SmartServo reference on the broader troubleshooting approach — SmartServo Delta servo troubleshooting summary — is the most readable practical walk-through, and the click2electro reference on the ASDA-B2 fault codes — click2electro Delta ASDA-B2 servo drive fault codes list — is the most complete code-by-code reference for the ASDA-B2 specifically. The Delta product page at Delta Electronics servo systems product pagehas the official product manuals and alarm code reference cards for the full Delta Servo Drive range.

For partner integrators who are running an active fleet, the diagnostic path is the same regardless of drive vendor — the six families apply to any servo drive that follows the IEC 61800 alarm-code naming, which is the vast majority of industrial servo drives on the market. The specific alarm-code numbers vary across vendors (AL001 in Delta is roughly equivalent to ER.001 in Yaskawa and AL.001 in Mitsubishi), but the family grouping is the same.

Closing: the alarm code is the symptom, the family is the diagnosis

Servo drive alarm codes look like a long list until they are grouped by root cause into the six families. Because the diagnostic logic is family-level rather than alarm-code-level, the operator who learns the six families can troubleshoot any new alarm code in the family without having memorised the specific code.

For partner distributors and OEMs who are running the alarm-code map across a fleet, the diagnostic path is the same regardless of drive vendor. For partner integrators who are commissioning a new machine, the diagnostic path is the same regardless of the application. For partner service teams who are training a new technician, the six families are the right entry point — the technician learns the six families in an afternoon and can troubleshoot the vast majority of field alarms on the first service call.

For partner distributors and OEMs who want to walk through the alarm-code map on a specific Delta VFD-VL integration, the Delta VFD-VL series product page has the official reference card, and the VICKS engineering team at the VICKS technical support contact page is the fastest path to a clean integration on a new hydraulic press, injection molding, or die casting machine.