Inovance IS620P/N Series Servo System Common Fault Diagnosis Guide: Fault Alarm Codes, Phenomena Analysis and Troubleshooting

Introduction to IS620P/N Fault Diagnosis

The Inovance IS620P/N series servo system is widely deployed in industrial automation applications ranging from CNC machine tools to packaging machinery. While the platform is engineered for reliability, field conditions such as electrical interference, mechanical wear, environmental stress, and configuration errors can trigger fault alarms or operational anomalies. This article provides a systematic guide to diagnosing and resolving the most common fault conditions encountered with the IS620P (pulse/train interface) and IS620N (EtherCAT communication) servo drives, based exclusively on the official IS620P/N Series Servo System Common Fault Treatment manual.

The fault diagnosis methodology presented here follows a structured approach: first, identify whether the drive has generated a fault alarm code (Er.xxx) or whether the problem manifests as an operational anomaly without an alarm; second, narrow down the root cause using the diagnostic tables and measurement procedures; third, apply the prescribed corrective action. This systematic approach minimizes trial-and-error troubleshooting and reduces mean time to repair.

1. Fault Alarm Codes Reference

The IS620P/N drive generates fault alarm codes in the format Er.xxx, where the numeric portion identifies the specific fault category. Faults are classified into alarm-type faults, which stop motor operation and require explicit reset, and warning-type faults, which alert the operator but do not necessarily stop operation. The following table provides a comprehensive reference of all major fault alarm codes documented in the IS620P/N fault treatment manual.

Fault Code	Fault Name	Primary Cause Category
Er.102	Encoder disconnection	Encoder cable wiring error, cable damage, PS+/- line abnormal, 5V/GND reverse connection, parameter setting error, drive-side fault
Er.108	Encoder phase error	Encoder cable mismatch, motor model mismatch, encoder damage
Er.120	Encoder communication error	Encoder cable松动, communication interference, encoder ROM data corruption
Er.121	Absolute position mode product mismatch	Single-turn encoder set as multi-turn, motor number setting error
Er.122	Absolute position mode product match fault	Motor not matching multi-turn absolute encoder, motor number incorrect
Er.130	DI function duplicate assignment	Same DI function assigned to multiple DI terminals, DI function number exceeds valid range
Er.136	Encoder ROM data verification error	Encoder cable wiring error, cable damage, PS+/- line abnormal, 5V/GND reverse, parameter error, drive-side fault, terminal contact poor
Er.201	Hardware overcurrent (overcurrent 2)	Drive inverter bridge shoot-through, current detection circuit abnormal, parameter setting error, motor cable short, motor burnout
Er.208	FPGA system sampling timeout	MCU communication timeout (H0B-45=1208), encoder communication timeout (H0B-45=2208), current sampling timeout (H0B-45=3208), high-precision AD conversion timeout (H0B-45=4208)
Er.210	Output ground short circuit	Power cable UVW to PE short, motor UVW to PE short, drive inverter bridge shoot-through, STO terminal not connected
Er.234	Fly-run (runaway)	Power cable phase sequence error, vertical axis gravity overload, rotor initial phase detection error, encoder model error, encoder wiring aging
Er.400	Main circuit overvoltage	Input voltage exceeding specification, regenerative energy exceeding braking resistor capacity, braking resistor damaged or parameter mismatch
Er.410	Main circuit undervoltage	Input voltage below specification, power supply capacity insufficient, main circuit cable contact poor, bus capacitor degradation
Er.420	Main circuit phase loss	Input phase loss, power cable loose, magnetic contactor fault
Er.430	Control circuit undervoltage	Control power supply unstable or power-off, control cable contact poor
Er.500	Overspeed	Motor cable UVW phase sequence error, H0A-08 overspeed threshold setting error, input command exceeding threshold, motor speed overshoot, drive fault
Er.610	Drive overload	Parameter setting error (H01-02, H00-05), gain/rigidity setting unreasonable, load inertia too large, mechanical jam, brake not released, motor stall, 660 overload curve too small
Er.620	Motor overload	Excessive load torque, motor capacity insufficient, mechanical jam, gain setting unreasonable, brake not opened, motor demagnetization, motor internal short/open
Er.630	Stall motor overheat protection	Motor stall due to mechanical jam, excessive load, limit switch position error, motor damage, encoder abnormal
Er.650	Heatsink overheat	Ambient temperature too high, parameter setting error, drive installation spacing/direction improper, fan failure, hardware fault, overload with improper reset
Er.731	Encoder battery failure	Battery not connected during power-off, battery polarity reversed, single-turn encoder set as multi-turn, battery voltage too low, battery cable short or open
Er.740	Encoder interference	Encoder cable not shielded or routed near power cables, encoder terminal contact poor, encoder cable aging
Er.920	Braking resistor overload	Internal resistor parameter modified from factory value, resistor quality defect, external resistor rating/parameter mismatch, resistor quality issue
Er.B00	Excessive position deviation	Position command exceeding tracking capacity, excessive load torque, gain settings too low, electronic gear ratio error
Er.B01	Excessive position command	Input pulse frequency exceeding H0A-09 maximum, input pulse interference, improper pulse cable shielding/grounding
Er.E08	EtherCAT synchronization loss (IS620N only)	Communication cable interference or breakage, drive internal network transformer fault, main station synchronization signal loss, EtherCAT sync interrupt tolerance too small

2. Detailed Fault Diagnosis for Critical Alarm Codes

2.1 Er.102 and Er.136: Encoder Disconnection and ROM Data Error

Er.102 (encoder disconnection) and Er.136 (encoder ROM data verification error or missing parameters) share overlapping root causes and diagnostic procedures. Both faults indicate a breakdown in communication between the drive and the motor encoder via the CN2 connector. The diagnostic approach follows a systematic elimination process.

First, perform a cross-validation test: connect a known-good motor and encoder cable to the drive. If the fault persists, the problem is drive-side; if the fault clears, the problem is in the original motor or cable. For cable-side diagnosis, use a multimeter to perform four key measurements. Measurement one: check the impedance between PS+ and PS- at the motor-side encoder connector. A reading of approximately 100 ohms indicates normal connection; infinite resistance indicates an open circuit; very low resistance (a few ohms) indicates a short circuit. Measurement two: check the impedance between +5V and GND at the motor side. A reading of approximately 2 kilohms indicates normal; infinite resistance or near-zero resistance indicates damage. Measurement three: verify pin-to-pin continuity of the encoder cable between the DB9 drive-side connector and the motor-side connector (AMP 9-pin or MIL-DTL-5015 military connector). Measurement four: flex the encoder cable while monitoring for intermittent fault triggers, which indicate broken wires or poor terminal crimping.

If the cable tests pass, check the encoder parameter settings. Parameter H00-04’s first two digits indicate the encoder type: 18 for magnetic encoder, 23 for optical encoder. For magnetic encoder motors, H00-00 (motor number) must be set to 14101. If the motor nameplate indicates a 20-bit incremental encoder but the drive is configured for a 23-bit absolute encoder, or vice versa, the encoder type mismatch will trigger these faults.

If all external checks pass and the fault persists, the drive’s CN2 port or internal encoder interface circuit may be damaged. In this case, replace the drive. If the encoder parameters are missing from the encoder ROM (checkable by verifying whether H00-04 and motor parameters are complete), the encoder itself has lost its stored data and the motor must be replaced.

2.2 Er.201 and Er.210: Hardware Overcurrent and Output Ground Short

Er.201 (hardware overcurrent) is one of the most severe fault codes, indicating that the drive’s hardware overcurrent protection has been triggered. This typically means the instantaneous output current has exceeded the drive’s maximum protective threshold, often due to a short circuit in the power output stage or load side. Er.210 (output ground short) is a related fault indicating that one or more output phases have shorted to ground.

The diagnostic procedure begins with a cross-validation test: disconnect the motor power cable from the drive, connect only the encoder cable, and power on the drive. If the fault persists without any motor connected, the drive’s inverter bridge is likely damaged. To confirm inverter bridge damage, use a multimeter in diode mode to test the freewheeling diodes and IGBT modules. For the upper bridge: place the black probe on P+ and the red probe on each of U, V, W in sequence. Normal readings should be between 0.3V and 0.7V. Then switch to resistance mode: red probe on P+, black probe on U/V/W. Normal readings should be at the megohm level. For the lower bridge: red probe on the negative bus terminal, black probe on U/V/W in diode mode (normal: 0.3V to 0.7V), then reverse in resistance mode (normal: megohm level). Any deviation from these readings indicates IGBT or diode damage, requiring drive replacement.

If the cross-validation test clears the fault (no alarm with motor disconnected), the problem is in the motor or power cable. Test the power cable for UVW-to-PE short circuits by disconnecting the cable from both the drive and motor, then measuring resistance between each phase (U, V, W) and PE. Any non-infinite reading indicates a cable short. Test the motor for internal short circuits by measuring UV, UW, and VW phase-to-phase resistance. The three readings should be approximately equal and should not exceed 10 ohms. If the readings are unequal or a phase-to-phase resistance is below 1 ohm, the motor windings are shorted and the motor must be replaced.

For Er.210 specifically, also verify that the drive model parameter H01-02 is correctly set. If the drive is an STO (Safe Torque Off) model but the STO terminals are not connected, or if H01-02 contains an incorrect model code, Er.210 may be falsely triggered. Connect the STO terminals and set H01-02 to match the drive nameplate.

2.3 Er.234: Fly-Run (Runaway)

Er.234 is triggered when the drive detects that the motor is rotating in an uncontrolled manner, typically due to loss of electromagnetic control over the rotor. This is a safety-critical fault, particularly on vertical axes where uncontrolled descent can cause equipment damage or personnel injury.

The most common cause is incorrect power cable phase sequence. The motor’s U, V, W terminals must correspond exactly to the drive’s U, V, W output terminals. If any two phases are swapped, the motor will rotate in the reverse direction from the commanded direction, and the drive will interpret this as a fly-run condition. Verify the phase correspondence at both the drive and motor ends of the power cable, referring to the connector pin assignments in the design and maintenance manual.

On vertical axes with gravity loads, excessive load torque can exceed the motor’s holding capability, causing the motor to be pulled downward by gravity. In this case, adjust the brake parameters H02-09 through H02-12 (brake output ON delay, brake OFF delay in stationary state, brake OFF speed threshold in rotating state, and servo-enable OFF to brake OFF delay). If the problem persists, reduce the vertical axis load, increase the system rigidity, or, as a last resort, disable the fly-run protection by setting H0A-12=0 (use with caution, only when safety is assured).

If the fault occurs immediately upon servo enable with correct phase sequence, the rotor initial phase detection may be erroneous due to electrical interference during power-on. Perform angle identification (H0D-04=1) and re-apply power. Also check the encoder cable for aging, corrosion, or loose connectors by disabling the servo enable, manually rotating the motor shaft, and observing whether H0B-10 (encoder position feedback) changes appropriately.

2.4 Er.400 and Er.410: Main Circuit Overvoltage and Undervoltage

Er.400 (main circuit overvoltage) occurs when the DC bus voltage exceeds the drive’s overvoltage protection threshold. For 220V-class drives, this threshold is approximately 400V DC; for 380V-class drives, approximately 800V DC. The most common cause is regenerative energy from motor deceleration exceeding the braking resistor’s energy absorption capacity. Verify that the braking resistor is correctly sized using the braking energy calculation: if the motor decelerates from rated speed to zero with a load inertia N times the motor inertia, the braking energy is (N+1) times EO (the motor’s rated braking energy), and the required resistor power is 2 times the quantity of (N+1) times EO minus EC (the capacitor’s maximum absorption energy), all divided by the reciprocating motion period T.

If an external braking resistor is used, verify that H02-26 (braking resistor resistance) and H02-27 (braking resistor power) match the actual resistor specifications. Setting these parameters to values larger than the actual resistor will cause the resistor to overload. For internal braking resistors, verify that the parameters have not been modified from factory values; restore H02-22, H02-23, H02-24, and H02-25 to factory settings if they have been changed.

Er.410 (main circuit undervoltage) occurs when the DC bus voltage drops below the undervoltage threshold. For 220V-class drives, this is approximately 200V DC; for 380V-class drives, approximately 460V DC. Common causes include: input power voltage below specification (measure R-S, R-T, S-T phase-to-phase voltages to verify), power supply capacity insufficient (particularly during motor acceleration when inrush current causes voltage sag), loose main circuit cable connections, and bus capacitor degradation. If Er.410 occurs during light-load operation, suspect bus capacitor degradation and schedule capacitor replacement.

2.5 Er.500: Overspeed

Er.500 is triggered when the motor actual speed exceeds the overspeed fault threshold. The default threshold is 1.2 times the motor’s maximum rated speed (when H0A-08=0), or a user-defined value (when H0A-08 is non-zero and less than 1.2 times maximum speed). If the input command corresponds to a motor speed exceeding this threshold, the drive will report Er.500.

For position control mode with pulse input, verify that the pulse frequency and electronic gear ratio do not produce a motor speed exceeding the threshold. The motor speed in rpm equals the pulse frequency divided by the electronic gear ratio numerator, multiplied by 60, divided by the electronic gear ratio denominator and the encoder resolution. For speed control mode, verify that the speed command value and speed limit parameters (H06-06 through H06-09) are within the threshold. For torque control mode, verify that the speed limit threshold is set within the overspeed threshold.

If the motor speed overshoots the threshold during transient response (visible in the InoServoShop oscilloscope as a speed feedback spike), the gain settings are too aggressive. Perform gain adjustment or reduce the rigidity level by one or two steps. Motor cable phase sequence error can also cause Er.500, as the reversed rotation direction may cause the speed to appear as an excessive value relative to the command direction.

2.6 Er.610, Er.620, and Er.630: Overload and Stall Faults

Er.610 (drive overload), Er.620 (motor overload), and Er.630 (stall motor overheat protection) form a family of thermally-motivated fault codes. Er.610 is triggered when the drive’s internal thermal model calculates that the drive’s semiconductor junction temperature has exceeded the safe limit. Er.620 applies the same logic to the motor. Er.630 is specifically triggered when the motor is stalled (zero speed with non-zero command) for a duration that causes the thermal model to predict overheating.

For Er.610, first verify that H01-02 (drive model) and H00-05 (bus motor number) are correctly set. A mismatch between the drive model parameter and the actual drive will cause the overload curve to be incorrectly applied. Check the gain parameters (H08 group) and rigidity settings (H09-00, H09-01); excessively high gain can cause current oscillation that appears as overload. Monitor H0B-12 (average load rate): if it exceeds 80%, the drive is undersized for the application and a larger drive should be selected. Check for mechanical jam by observing whether the load exhibits sticking or binding during operation. Verify that the motor brake is released before the drive outputs torque; if the brake remains engaged while the drive commands torque, the resulting stall current will trigger Er.610.

For Er.620, in addition to the checks for Er.610, test the motor for demagnetization by performing motor self-learning and checking whether the back-EMF is approximately 300V (for G-series motors). For HV-series motors, if the current at rated torque significantly exceeds the motor’s rated current, demagnetization is confirmed and the motor must be replaced. Also test the motor windings for internal open circuits (by shorting UV, UW, VW in turn and rotating the shaft; 8 or 10 uniform cogging points per revolution indicate normal windings; absence of cogging indicates an open circuit) and internal short circuits (UV, UW, VW resistance below 1 ohm indicates a phase-to-phase short).

For Er.630, the primary diagnostic is to determine whether the motor is actually stalled. In RUN state, verify that the command is non-zero while H0B-00 (motor speed) reads zero. In position mode, check H0B-13 (input position command counter); in speed mode, check H0B-01 (speed command); in torque mode, check H0B-02 (internal torque command). If the drive is confirmed to be stalled, inspect the mechanical system for jamming, check whether limit switches are installed outside the travel range, and verify that the motor brake is opening properly (check for 24V at the brake output). Note that Er.630 can be falsely triggered if the stall protection parameter H0A-33 is set to 0 (disabled); in this case, re-enable stall protection and investigate the root cause of the stall.

2.7 Er.650: Heatsink Overheat

Er.650 is triggered when the drive’s heatsink temperature exceeds the overtemperature protection threshold. The threshold varies by drive model: 90 degrees Celsius for S1R6, S2R8, S5R5, S018, T017, T021, and T026 models; 95 degrees Celsius for S7R6, S012, T3R5, T5R4, T8R4, and T012 models. The diagnostic procedure addresses five potential causes.

First, measure the ambient temperature; if it exceeds the drive’s allowable maximum (55 degrees Celsius, with derating above 40 degrees), improve the cabinet cooling by adding forced air ventilation or air conditioning. Second, verify that H01-02 (drive model) is correctly set; an incorrect model parameter may cause the wrong overtemperature threshold to be applied. Third, inspect the drive installation: the drive must be vertically mounted with adequate lateral spacing (minimum 10mm for SIZE A/B, 25mm for SIZE C and above) and vertical clearance (minimum 50mm top and bottom). Fourth, check the cooling fan: observe whether the fan rotates freely during operation, and inspect for dust or debris blocking the airflow path. Clean with compressed air if needed; replace the drive if the fan has failed. Fifth, check for overload history: query the fault log (set H0B-33 to select the fault record number, then read H0B-34) for prior overload faults (Er.610, Er.620, Er.630, Er.650, Er.909, Er.920, Er.922). If overload faults have been repeatedly reset by power cycling, the accumulated thermal stress may have damaged the heatsink or power module; wait 30 seconds after overload before resetting, and address the root cause of the overload.

For hardware verification, check the temperature sensor reading at cold power-on: H0B-27 (heatsink temperature) should be within 10 degrees of ambient temperature. A large discrepancy indicates a temperature sensor or ADC fault, requiring drive replacement.

2.8 Er.731: Encoder Battery Failure

Er.731 is specific to motors with multi-turn absolute encoders. It indicates that the external battery voltage has dropped below the alarm threshold (2.85V to 3.15V) or that the battery circuit is faulty. The battery (model S6-C4, 3.6V lithium, 2600mAh capacity) maintains multi-turn position data when the drive is powered off.

Diagnostic steps: First, verify that the battery was connected during the power-off period. If the battery was disconnected, reconnect it and set H0D-20=1 to clear the fault. Second, check the battery cable polarity: the blue wire connects to positive and the blue-black wire connects to negative at the encoder side. Reversed polarity will prevent the battery from powering the encoder and may damage the encoder circuit. Third, verify that the encoder type matches the configuration: if the motor nameplate indicates U2 (single-turn encoder) but H02-01 is set to 1 (multi-turn mode), the drive will expect a battery that does not exist. Set H02-01 to 0 for single-turn encoders. Fourth, measure the battery voltage: if it is below 2.85V, replace the battery with a new S6-C4 unit. Fifth, measure the battery cable impedance: infinite resistance between the positive and negative terminals indicates an open circuit (check the cable and encoder internal wiring); near-zero resistance indicates a short circuit (replace the encoder or motor if the short is internal to the encoder).

2.9 Er.E08: EtherCAT Synchronization Loss (IS620N Only)

Er.E08 is specific to the IS620N EtherCAT variant. It indicates that the EtherCAT distributed clock synchronization has been lost, typically due to communication signal interference or physical connection problems. The IS620N’s display panel provides diagnostic information through the leftmost seven-segment digit: the upper dash indicates PORT1 (OUT) connection status and the lower dash indicates PORT0 (IN) connection status. A solid dash indicates an established physical link; a dark dash indicates no link; a blinking dash indicates an unstable physical connection, often caused by a faulty network transformer inside the drive.

For Er.E08 diagnosis, read the EtherCAT error counter parameters H0C-36 through H0C-40. H0C-36 (corresponding to register addresses 0x300/0x301) counts IN port receive errors: the low byte indicates CRC errors and the high byte indicates PHY-to-ET1100 errors. H0C-37 (0x302/0x303) counts OUT port receive errors with the same byte structure. H0C-38 (0x308/0x309) counts data forwarding errors. H0C-39 aggregates all port error counts. H0C-40 (0x310/0x311) counts link losses, with the low byte for PORT0 (IN) and the high byte for PORT1 (OUT).

If the error counters increment during motor operation but not at rest, the cause is electromagnetic interference. Remediation includes: using shielded Category 5e or higher Ethernet cables with Inovance-specified or equivalent quality, ensuring proper PE grounding at both the drive and controller ends, separating EtherCAT cables from motor power cables, and updating to the latest XML device description file (version 2.6.8 or later, which includes improved E08 alarm suppression). If the error counters increment even when the motor is not running, the drive’s internal EtherCAT hardware is likely damaged and the drive should be replaced. If multiple stations simultaneously report Er.E08, check the master controller for software errors or stoppage.

3. No-Alarm Fault Phenomena Analysis

Not all servo system problems generate fault alarm codes. The IS620P/N fault treatment manual documents numerous operational anomalies that occur without an Er.xxx alarm. These phenomena require different diagnostic approaches, as the drive itself does not identify the problem.

3.1 Panel Not Displaying

If the seven-segment display shows nothing after control circuit power is applied, first measure the voltage between L1C and L2C to verify it is within specification (220V plus or minus 10% for 220V drives, 380V plus or minus 10% for 380V drives). If the voltage is correct, disassemble the drive’s plastic enclosure and check the ribbon cable connecting the control board to the power/drive board. A loose ribbon cable is the most common cause of blank display. If the ribbon cable is secure, measure the voltage at display connector J10 pins 4 and 5: a reading of +5V indicates the power supply is functioning and the display board itself is faulty; no voltage indicates the switching power supply circuit has failed. Both conditions require drive replacement.

3.2 Motor Does Not Rotate

If the motor does not rotate after servo enable and motion command, first verify that a non-zero command is being received. For IS620P, use the InoServoShop software to check the position or speed command value. For IS620N, check the panel display: the communication state should show 8 (operational), the control mode should match the expected mode, and the servo state should show “rn” (run). If the state shows “ry” (ready) instead of “rn” (run), the mode-of-operation object (6060h) may not have been written by the master, or the master may be sending zero data.

If a non-zero command is confirmed and the motor still does not rotate, check for: motor brake not released (verify 24V at brake output and manual rotation capability), mechanical jam (observe for physical obstruction), motor internal short or open circuit (perform winding resistance tests as described for Er.620), or DI signal configuration errors that may be inhibiting operation (check H03 group DI function assignments and the corresponding DI signal states). If the drive generates an alarm during this process (such as Er.603, Er.610, Er.630, or Er.B00), follow the alarm-specific diagnostic procedure.

3.3 Low-Speed Rotation Instability

If the motor rotates but exhibits unstable behavior at low speeds (typically below 100 rpm), the gain settings are likely inappropriate. Perform auto gain adjustment per section 6.5 of the design and maintenance manual: ensure the correct load inertia ratio is set in H08-15, set H09-00 to 1 (parameter self-tuning mode), and incrementally adjust H09-01 (rigidity level) while observing the motor’s low-speed behavior through the InoServoShop oscilloscope. If the motor shaft exhibits left-right oscillation at low speed, the load inertia ratio (H08-15) may be set too high; re-perform inertia identification.

3.4 Parameter Cannot Be Modified

If parameters cannot be modified through the operation panel, check the following conditions: the drive must be in stop state (not running) for most parameter changes; some parameters require the servo enable signal to be OFF; the user password (H02-30) may have been inadvertently set to a non-zero value (if H02-30 is set to 1, the panel displays five horizontal lines and parameters are locked; write 1 to H02-30 again to unlock, or perform factory reset with H02-31=1); and parameters that are automatically managed in auto-tuning mode (H09-00=1 or 2) cannot be manually modified until H09-00 is set to 0.

3.5 Brake Cannot Open

If the motor brake does not release when commanded, first verify that the DO function 9 (FunOUT.9: BK, brake output) is assigned to a DO terminal (typically DO5). Check the H02-09 through H02-12 brake timing parameters to ensure they are not set to excessively long delays. Measure the voltage between DO5+ and DO5-: 24V indicates the brake output is active; 0V indicates the output is inactive. If the output is active but the brake does not release, check the brake power supply (24V), the brake relay, and the brake cable continuity. The brake release time and engagement time vary by motor frame size: for example, ISMH1-10B has a 10ms release time and 30ms engagement time, while ISMH3-29C and larger motors have 100ms release time and 230ms engagement time.

3.6 Pulse Input Not Received

If the drive does not respond to pulse commands from the upper-level controller, determine whether the low-speed pulse port or high-speed pulse port is being used. For the low-speed pulse port (H05-01=0), verify that the pulse cable is connected to the PULSE+/PULSE- and SIGN+/SIGN- terminals, that the PULLHI terminal is properly connected for open-collector input mode, and that the upper-level controller’s ground is reliably connected to the drive’s GND (for differential input) or COM (for open-collector input). For the high-speed pulse port (H05-01=1), only differential input is supported; verify that HPULSE+/HPULSE- and HSIGN+/HSIGN- are correctly wired and that the controller’s ground is connected to the drive’s GND.

Use the drive’s input pulse counter (H0B-13) to verify pulse reception: if the counter increments when pulses are sent, the physical connection is good and the problem is in the electronic gear ratio or position control parameters. If the counter does not increment, the physical connection is faulty. Check for pulse cable breakage, incorrect wiring, and insufficient signal voltage levels.

4. Encoder and Motor Fault Diagnosis

4.1 Encoder Cable Pin Assignment Verification

The IS620P uses a DB9 connector for the CN2 encoder interface. The standard 20-bit incremental encoder pin assignment is: Pin 1 = PS+, Pin 2 = PS-, Pin 6 = +5V, Pin 8 = GND, Shell = PE. The IS620N uses the same DB9 interface but may also support 23-bit absolute encoders with additional battery pins. For motors with AMP 9-pin connectors (frame sizes 40, 60, 80), the pin assignment is: Pin 3 = PS+, Pin 6 = PS- (twisted pair), Pin 9 = +5V, Pin 8 = GND, Pin 7 = shield. For motors with MIL-DTL-5015 military connectors (frame sizes 100, 130, 180), the pin assignment uses letter designations: A = PS+, B = PS- (twisted pair), G = +5V, H = GND, J = shield.

When troubleshooting encoder faults, always verify that the cable’s pin assignment matches the connector type at both ends. Mismatched pin assignments between the DB9 drive-side connector and the motor-side connector will cause communication failures (Er.102, Er.120, Er.136) or, in the case of +5V/GND reversal, permanent encoder damage.

4.2 Motor Winding Tests

Motor winding integrity is tested using a multimeter in resistance mode. For phase-to-phase resistance, measure UV, UW, and VW in turn. All three readings should be approximately equal. Readings below 1 ohm indicate a phase-to-phase short circuit within the motor. Readings that are infinite indicate an open winding. Unequal readings (differing by more than 10%) indicate partial winding damage. For phase-to-ground insulation, measure the resistance between each phase (U, V, W) and PE. All readings should be at the megohm level; readings below 1 megohm indicate insulation breakdown.

A mechanical test for winding integrity involves shorting two phases together (UV, then UW, then VW) and manually rotating the motor shaft. A healthy motor will exhibit 8 or 10 uniform cogging points per revolution due to the detent torque created by the shorted windings. If no cogging is felt, the winding is open. If the cogging is uneven, the windings may be partially shorted.

5. Systematic Troubleshooting Flowchart

The following flowchart provides a structured approach to diagnosing any IS620P/N servo system problem, whether or not a fault alarm code is present.

Step 1: Fault Code Check. If the drive’s display shows an Er.xxx code, proceed to the corresponding section in the fault alarm code reference table. If no alarm code is displayed but the system is not functioning correctly, proceed to Step 2.

Step 2: Power Verification. Measure the control circuit voltage (L1C-L2C) and main circuit voltage (R-S, R-T, S-T or L1-L2). Verify that the voltages are within the drive’s specification range. If voltages are out of range, address the power supply before continuing.

Step 3: Parameter Verification. Check H00-00 (motor number) against the motor nameplate. Check H01-02 (drive model) against the drive nameplate. Check H02-02 (control mode) against the application requirement. Check H02-01 (encoder type) against the encoder specification. Incorrect parameter settings are the cause of a significant percentage of field faults.

Step 4: Cable and Connection Inspection. Visually inspect all cables for damage, loose connectors, and correct routing. Verify that power cables and signal cables are separated. Verify that shielded cables are used for encoder and communication connections. Verify that all terminal screws are tightened to specification.

Step 5: Cross-Validation. If the problem persists after Steps 1-4, perform a cross-validation test by substituting known-good components (motor, encoder cable, power cable, or drive) one at a time. This isolates whether the fault is in the drive, motor, or cable.

Step 6: Software Diagnosis. Use the InoServoShop (InoDriverShop) debugging software to monitor real-time parameters including motor speed (H0B-00), speed command (H0B-01), torque command (H0B-02), bus voltage (H0B-07), average load rate (H0B-12), input position command counter (H0B-13), and heatsink temperature (H0B-27). Use the oscilloscope function to capture waveforms for detailed analysis of transient behavior.

Step 7: Component-Level Testing. If the fault is isolated to a specific component, perform the component-level tests described in this article: multimeter diode tests for the drive’s inverter bridge, resistance tests for motor windings, impedance tests for encoder circuits, and voltage tests for brake and DO outputs.

Step 8: Resolution and Documentation. After identifying and resolving the root cause, document the fault, root cause, and corrective action for future reference. If the fault is likely to recur (e.g., environmental interference, undersized drive), recommend systemic improvements such as cable rerouting, drive upsizing, or installation of additional shielding.

6. EtherCAT Communication Fault Diagnosis (IS620N)

The IS620N variant uses EtherCAT for real-time communication with the master controller. EtherCAT faults manifest as communication loss, synchronization errors (Er.E08), or motor control anomalies due to delayed or missing command data. The IS620N’s panel display provides real-time EtherCAT status information through a five-digit LED display: the first digit shows the PORT0 (IN) and PORT1 (OUT) connection status via upper and lower dash marks, the second digit shows the communication state (0=invalid, 1=initializing, 2=pre-operational, 4=safe-operational, 8=operational), the third digit shows the control mode (1=profile position, 3=profile velocity, 4=profile torque, 6=homing, 8=cyclic sync position, 9=cyclic sync velocity, A=cyclic sync torque), and the remaining digits show the servo state (nr=not ready, ry=ready, rn=run).

If the communication state does not reach 8 (operational), verify that the master controller has completed the EtherCAT state machine transition sequence: INIT to PREOP to SAFEOP to OP. If the state is stuck at 1 (initializing), check the physical cable connection and the slave’s device description file (XML). If the state is 2 (pre-operational) but does not advance, the master may not be sending the required mailbox communication for configuration. If the state is 4 (safe-operational) but does not advance to 8 (operational), the process data object (PDO) mapping may be incorrect or the distributed clock synchronization may not be established.

If the panel shows “=80ry” (cyclic sync position mode, ready state) but the motor does not run, the master is sending zero position commands. Write 8 to object 6060h (mode of operation) to select cyclic sync position mode, and verify that the target position (607Ah) is being sent. If the panel shows “=88rn” (cyclic sync position mode, run state) but the motor does not move, check the torque limit objects 60E0h and 60E1h (recommended: 3000, representing 300% rated torque). Also verify that the position command unit matches the drive’s configuration: the IS620N uses command units (encoder counts) as the position command unit.

Conclusion

Effective fault diagnosis of the Inovance IS620P/N servo system requires a methodical approach that combines parameter verification, physical measurement, cross-validation testing, and software-based waveform analysis. The key principles are: always verify parameters before suspecting hardware failures; always perform cross-validation to isolate the faulty component; always use the InoServoShop oscilloscope for transient fault analysis; and always document the root cause and corrective action for future reference. By following the systematic flowchart and detailed diagnostic procedures presented in this guide, maintenance personnel can significantly reduce troubleshooting time and improve the overall reliability of servo-driven automation systems.