CNC Servo Motor Failure Symptoms and Diagnostic Methods

Introduction to Servo Motor Failure and Operational Risks

When a CNC servo motor experiences a sudden loss of holding torque or electrical isolation, the immediate physical consequence on the shop floor is a catastrophic event: a heavy vertical axis drops unexpectedly under its own weight, or a high-speed axis plunges a cutting tool directly into a solid vise jaw, chuck, clamp, or rotary turret. Within milliseconds, this uncontrolled servo deviation or stalled state destroys the cutting tool, shatters the workpiece, bends precision ball screws, and leaves a ruined scrap part in the machining envelope. On the electrical side, cutting fluid pooling around compromised connectors eventually permeates the housing to degrade insulation resistance, culminating in a violent phase-to-ground short circuit that permanently destroys expensive drive amplifiers.

On high-speed production lines, forcing a machine to run while a clogged fan has stopped or ignoring an abnormal vibration can cause the servo amplifier to overheat. When the drive amplifier disables itself and drops its ready signal (VRDY OFF), the dynamic brakes abruptly halt the axis, resulting in extended stopping distances and violent machine collisions. Technicians must understand the underlying parameters, hardware signals, and diagnostic interfaces of Fanuc, Siemens, and Mitsubishi systems to intercept these failure sequences before they trigger total hardware destruction.

Technical Summary of Servo Diagnostics

Command / Code	Brands	Critical Parameters	Main Constraints and Diagnostic Tools
G00, G01, G04, G31, LIMS, MSG, SPOS, M03, M19	Fanuc, Siemens, Mitsubishi	Parameter 1828 (Move deviation), Parameter 1829 (Stop deviation), p1082 (Overspeed limit), SV022 (Overload level)	Always keep cabinet power ON during active overload cooling; verify holding brake torque before enabling servo off axis detach; check FSSB fiber-optic cables when communication drops.

Quick Read: Key Maintenance Decisions

• Never cycle control power to clear active overload alarms. Turning power OFF and ON to force a reset on active Overload 1 (Alarm 50) risks permanently destroying motor windings; keep power ON so internal fans can cool the power modules.
• Measure phase-to-ground insulation resistance with a megohmmeter. Technicians must physically disconnect motor power cables at the amplifier and test the U, V, and W wires before resetting short-circuit alarms like SV0438 to avoid destroying replacement drives.
• Differentiate position deviation registers by control generation. On Fanuc controls, monitor deviation on DGN 800 to 803 for legacy Series 0-C, and DGN 300 for newer 30i-B and 0i-F series.
• Match safety parameters and firmware versions. Ensure SINAMICS firmware versions >= 4.7 with p9567 > 0 are matched with compatible SINUMERIK controls to prevent data cross-check errors.
• Validate thermal limits manually on sensorless drives. When retrofitting or servicing Mitsubishi MDS-B-HR series motors without built-in sensors, parameter SV034/bit2 must be manually set to 1 to activate thermal estimation.
• Observe load meter fluctuations during cutting feed. Instantly pause operations if the axis load meter sways over 120% to investigate mechanical binds or tool wear before an Alarm 50 or Alarm 59 collision shuts down the channel.

Basic Concepts of Servo Loop Performance

Diagnosing Fanuc servo motor failures requires monitoring mechanical loads, cutting conditions, and ambient environments. Running the motor under excessively severe conditions or ignoring a failing mechanical bearing generates excessive load torque. Under these conditions, the digital servo software actively detects the abnormal current or thermal state and throws an alarm code, stopping operation. Safe use notes stress monitoring vertical axes during power-loss or alarm troubleshooting; if a vertical axis loses holding torque or experiences a brake failure while maintenance personnel are inspecting the cabinet, the axis can unexpectedly drop, causing severe injury or a major crash.

Electrical failure pathways are often caused by fluid penetration around electrical connectors. Similar to issues observed in M08 coolant flow faults, ignoring fluid pooling around electrical conduit channels leads to fluid permeating the motor housing, degrading the insulation resistance and creating phase-to-ground short circuits. To recover safely from current alarms, technicians are instructed to never simply reset the machine; they must physically disconnect the motor power lines and test phase-to-ground insulation resistance using a megohmmeter before applying power.

Feedback and control tuning are critical to suppressing motor hunting, shaft swaying, and machine resonance. If speed loop gains (such as speed loop gain 1 or speed loop integral compensation) are incorrectly adjusted, the servo drive will experience tracking error and high-frequency gear noise. If encoder pulse feedback is corrupted or configured with an incorrect pulse count, the axis can accelerate uncontrollably, compromising the holding devices like a chuck or vise jaw, and causing the workpiece to slip during heavy interpolation.

Command Structure and Diagnostic Parameter Mappings

The execution of motion commands on modern CNC systems requires tight synchronization between the controller's software trajectory generator and the drive amplifier's physical servo loop. Diagnostic parameters dictate the permissible deviation between the commanded mathematical path and the actual physical encoder feedback. When this difference exceeds the programmed thresholds during G00 or G01 moves, the drive interrupts the command sequence to protect the axis drivetrain.

Technicians must utilize system menus to read active diagnostics when analyzing servo performance. For instance, the Fanuc [SYSTEM] menu allows direct inspection of position deviation values, while Siemens systems use dynamic HMI variables to display faults. Similarly, Mitsubishi amplifiers use physical displays to output diagnostic codes, facilitating local troubleshooting at the electrical cabinet.

The system parameters and diagnostic addresses are organized systematically across different CNC systems, ensuring that tracking errors and parameters are mapped correctly to prevent overspeed or overcurrent states.

• Fanuc: Accesses registers via the [SYSTEM] to [DGNOS] menus. The diagnostic bits represent physical states such as contactor status, thermal warnings, or encoder disconnections.
• Siemens: Communicates drive integrity through dynamic context and parameters like actual speed and stall delay limits on the SINAMICS HMI interface.
• Mitsubishi: Relies on diagnostic parameters and hardware displays to evaluate axis drift and loop gain adjustments on HMI monitor screens.

Brand Applications: Fanuc, Siemens, and Mitsubishi Systems

Fanuc

Fanuc systems rely heavily on diagnostic registers and deviation tracking parameters to monitor servo loop behavior. Parameter 1828 sets the moving deviation limit, while Parameter 1829 monitors the stop deviation. Technicians must check these registers when a movement alarm occurs.

During diagnostic operations, standard movement blocks like G00 X150.0 Y150.0; and G01 Z-50.0 F250.0; are executed to induce axis travel, while a dwell command like G04 X2.0; lets the technician observe position error settling under static conditions. The skip command G31 P99; is utilized to test high-speed digital inputs and torque responses.

Parameter / Register / Alarm / Version	Details / Source Data
Parameter 1825	Servo loop gain for each axis, standard setting value is typically 3000.
Parameter 2022	Motor rotation direction; accepts values 111 (Counterclockwise) or −111 (Clockwise).
Parameter 3111 Bit 0 (SVS)	Bit switch (0 or 1) to show or hide the internal servo tuning screen.
Parameter 1807 Bit 2	Bypasses cooling fan stopped check (0 or 1).
Parameter 1023	Servo Axis Number sequence mapping.
Parameters 2084 / 2085	Flexible feed gear parameters (numerator and denominator).
DGN 200	Bit-level flags (OVL, LV, OVC, HCA, HVA, DCA, FBA, OFA) showing hardware conditions.
DGN 201	Binary flags ALD and EXP for pulse coder / encoder state.
DGN 204	Binary flags OFS, MCC, LDA, and PMS for amplifier state.
DGN 300	Position errors and deviation tracking.
Alarm SV0400	Servo motor or amplifier has overheated (hardware thermostat or thermal estimation).
Alarm SV0411	Positional deviation during movement exceeds Parameter 1828 limit.
Alarm SV0438	Excess motor current in main circuit or inverter.
Alarm SV0436	Soft thermal OVC (overload) alarm.
Alarm SV0415	Motion value overflow when velocity command exceeds 511,875 detection units/sec.
Alarm SV0004	Excess error during G31 torque limit skip.
Version - 30i-B, 0i-F, Power Motion i-A	Smart Troubleshooting interface (Trouble Diagnosis Guidance, Monitors, Graphic screens) exclusively with alpha i-B amplifiers.
Version - Series 0-C vs. Newer	Position deviation monitoring is under DGN 800 to 803 on Series 0-C, whereas newer systems use DGN 300.
Version - ROM 9040 series	Allows Series 0-C to differentiate built-in pulse coder vs. separate pulse coder disconnects.

Warning: Bypassing parameter 1807 Bit 2 to ignore a stopped cooling fan will lead to severe amplifier overheating. If the ready signal (VRDY OFF) drops at high speeds, dynamic braking will extend axis stopping distance, risking a tool blowout or severe machine crash.

Siemens

Siemens controllers monitor drive integrity through active speed parameters and temperature sensors. Technicians monitor speed parameter p1082 and delay parameter p2178 to manage motor stall limits.

Safety boundaries can be set in Siemens programs using commands like LIMS=3000, and user messages can be output to the HMI via MSG("Check motor load and torque limits"). Axis dwell is achieved using standard M0 program stops, and orienting spindles before heavy cycles uses SPOS=0 positioning.

Parameter / Register / Alarm / Version	Details / Source Data
Parameter p0604 / p0605	Motor temperature alarm and fault thresholds (for KTY84 or PT1000 sensors).
Parameter r0063	Actual speed of the motor in RPM (read-only).
Parameter r1408.11 / r1408.12	Control words used by internal logic to detect stall conditions (speed and flux difference bits).
Parameter p9567	Crosswise data comparison parameter.
Parameter p0640	Current limits (Amps / Percent).
Alarm F7900 / 207900	Motor blocked / speed controller at limit (torque limit for >1 sec and speed remains under 120 rpm).
Alarm F7901 / 207901	Motor overspeed exceeding limits set by parameter p1082.
Alarm 207902	Motor mechanically stalled for a duration exceeding parameter p2178.
Version - SINAMICS FW >= 4.7	Expanded crosswise data comparison list when parameter p9567 > 0; must match compatible SINUMERIK control to prevent data errors.
Version - Power Unit FW < 5.1	Fan fault alarm value defaults to 0, mapping all heat sink warnings directly without distinguishing individual fan modules.
Hardware LED	— (no source)

Warning: Entering an encoder pulse count that is too small during commissioning causes uncontrollable spindle acceleration, which can compromise a chuck or vise jaw, causing workpieces to fly out of the machining channel.

Mitsubishi

Mitsubishi drives leverage loop gains and detection widths to track positioning accuracy. The speed loop gain #2205 SV005 VGN1 and speed loop integral compensation #2208 SV008 VIA are critical parameters adjusted to eliminate shaft swaying and hunting.

Diagnostic programs use dwelled movement checks such as G04 X1.0 ; to observe tracking errors. Technicians can execute standard spindle start cycles with S1000 M03 ; or trigger coordinate orienting routines like M19 ; to test positioning feedback.

Parameter / Register / Alarm / Version	Details / Source Data
Parameter #2221 SV021	Overload detection time constant (Standard setting: 60).
Parameter #2222 SV022	Overload detection level (Standard setting: 150%).
Parameter #2226 SV026	Excessive error detection width during servo OFF, calculated as (RAPID / (60 × PGN1)) / 2.
Parameter SV034/bit2	Motor thermal validation, set to 0 (Invalid) or 1 (Valid) in parameter settings.
Alarm 31	Motor speed exceeds allowable limit. Remedy via accel/decel constants or repair speed detector.
Alarm 46	Motor or detector thermal protection activates due to heavy load or clogged cooling fan.
Alarm 50	Overload detection level continuously exceeds 100% threshold.
Alarm 53	Position deviation during servo OFF exceeds parameter SV026 setting value.
Alarm 58	Disturbance torque exceeded during G00 Rapid Traverse mode.
Alarm 59	Disturbance torque exceeded during G01 Cutting Feed mode.
Alarm 88 / 888	Watchdog error indicating a critical system watchdog crash.
Version - MDS-B-HR series	Lacks built-in motor thermal sensor in some models, requiring parameter SV034/bit2 set to 1 to validate.
Version - MDS-D/DH vs. MDS-EJ/EJH	Watchdog error (Alarm 88) displays as "88" on MDS-D/DH but displays as "888" on MDS-EJ/EJH.
Hardware LED	Alternating 7-segment LED sequences on amplifiers (alarm class to 2-digit error no. to affected axis bit).

Warning: Bypassing axis detachment checks when evaluating mechanical brake holding torque will cause the vertical axis to drop instantly under its own weight, culminating in a severe collision if parameter #2226 SV026 is incorrectly calculated.

Brand Comparison Matrix

Feature / Category	Fanuc	Siemens	Mitsubishi
HMI / Diagnostic Menus	[SYSTEM] to [DGNOS] screens; bit-level registers showing diagnostic flags.	Structured diagnostic HMI displays using the standard <Location data> <Alarm text> format.	"SERVO MONITOR" and "SERVO DIAGNOSIS" screens; Part system / Section NC Memory Diagnosis screen.
Hardware LED Display	— (no source)	— (no source)	Alternating 7-segment LED sequences on amplifiers (alarm class to error number to affected axis bit).
Key Parameters	Parameter 1828 (Move deviation), Parameter 1829 (Stop deviation), loop gain Parameter 1825, rotation direction Parameter 2022.	Parameter p1082 (Maximum speed), p2178 (Stall delay), sensor parameters p0604 and p0605.	Loop gains #2205 (SV005 VGN1) and #2208 (SV008 VIA), overload settings #2221 and #2222, deviation width #2226 (SV026).
Thermal & Overload Detection	Alarms SV0400 (Overheat) and SV0436 (Soft Thermal OVC) evaluated via software thermostats or thermal estimation.	Internal software temperature modeling and alarm parameters p0604 and p0605 (supporting KTY84 or PT1000 sensors).	Alarm 46 (Motor overheat) and Alarm 50 (Overload 1); parameter SV034/bit2 validates motor thermal estimation.
Position / Blocked Detection	Alarm SV0411 (Excess deviation moving) relative to the mathematical limit in Parameter 1828.	Alarm F7900 / 207900 (speed controller at limit under 120 rpm) and Alarm 207902 (Drive stalled based on p2178).	Alarm 53 (Excessive error 2 during servo OFF) relative to calculated parameter #2226 SV026.
Safety & Braking Reactions	Dynamic brakes halt axis if ready signal drops (VRDY OFF), resulting in extended stopping distances.	Hardware-level OFF2 (instant pulse inhibit/coast) or OFF3 (fast braking ramp) drive safety reactions.	Dynamic deceleration control or electromagnetic brake holding torque safety sequences.
Collision Detection	Alarm SV0004 (Excess error during G31 torque limit skip) when physical limits are breached.	Torque limit controls (via parameter p0640) trigger blocks and shut down the machining channel.	Separate modal limits: Alarm 58 tracks Rapid Traverse (G00) and Alarm 59 tracks Cutting Feed (G01).
Troubleshooting Interface	"Smart Troubleshooting" graphical flowchart and YES/NO guides on 30i-B, 0i-F controls with alpha i-B amplifiers.	Granular internal fault and alarm values (reading native drive parameters r0949 and r2124).	HMI screens and PC-based diagnostic software ("MS Configurator" and "NC Analyzer2").

Technical Analysis of Diagnostic Architectures

Each CNC brand uses a proprietary architecture that separates it from standard parallel-wired servo systems. Fanuc utilizes a proprietary high-speed fiber-optic bus (FSSB) to daisy-chain all servo amplifiers together. When a communication fault occurs, system alarms identify the exact physical cable segment that failed between two specific amplifier nodes, visually mapping the broken link. To keep this communication channel robust, technicians must perform a comprehensive FSSB fiber optic troubleshooting routine to check for dirty or fractured fibers. Fanuc also integrates a Smart Troubleshooting function directly into the CNC interface, displaying a graphical flowchart that asks the operator YES/NO questions to trace faults. The bit-level flags in DGN 200 break down generic servo faults into specific flags, allowing technicians to instantly isolate physical or electrical failures.

Siemens distinguishes its servo diagnostic architecture by utilizing an exceptionally granular fault value system. Technicians read internal hexadecimal data natively from parameters r0949 and r2124, which explicitly pinpoints internal drive evaluation failures, such as complex phase short-circuits or encoder signal losses. Siemens also embeds deeply integrated hardware-level safety reactions, such as executing an immediate OFF2 coast-down or a fast OFF3 braking ramp, directly into the drive topology. This design ensures that the motor is paralyzed before a software-level PLC command is processed, preventing uncommanded servo deviations. Siemens also employs sophisticated internal motor temperature modeling and internal stall detection algorithms to catch mechanical binds before the hardware is destroyed.

Mitsubishi's approach to failure diagnosis relies on alternating 7-segment LED displays physically located on the drive amplifiers. These displays flash the alarm class, the two-digit error number, and the affected axis bit, allowing technicians to diagnose exact hardware faults directly from the electrical cabinet. Mitsubishi also categorizes motor collision detection into two distinct modal states: Alarm 58 tracks disturbance torque during rapid traverse, and Alarm 59 tracks it during cutting feed, dynamically separating high-speed inertial impacts from slow-speed heavy cutting limits. Technicians can use PC-based diagnostic and tuning environments, such as MS Configurator and NC Analyzer2, to sample high-speed waveform data and suppress machine resonance via notch filters without requiring external oscilloscope hardware.

Program Examples and Dry Run Verification

To verify the mechanical stability and electrical feedback loops of the servo axes, programmers run dedicated diagnostic programs. These examples demonstrate standard motion and pause sequences designed to track positioning deviation under controlled loads.

Fanuc Diagnostic Program Block

G00 X150.0 Y150.0 ;
G01 Z-50.0 F250.0 ;
G04 X2.0 ;
G31 P99 ;

Dry Run Description: When this block is executed, the CNC first commands a high-speed rapid positioning move to X150.0 and Y150.0. The axis then interpolates linearly down to Z-50.0 at a feedrate of 250.0 mm/min. At the end of the stroke, G04 pauses movement for 2.0 seconds, allowing the control loop to stabilize while technicians monitor position error on DGN 300. Finally, G31 initiates a torque-limit skip check; if a physical limit is hit before reaching the coordinate, the axis skips to the next block, preventing a severe collision.

Siemens Diagnostic Program Block

LIMS=3000
MSG("Check motor load and torque limits")
M0
SPOS=0

Dry Run Description: In this Siemens block, the maximum spindle speed is capped at 3000 rpm using LIMS=3000 to prevent centrifugal damage to the spindle chuck. The controller displays a custom message MSG on the screen prompting the operator to inspect the active loads. A program stop M0 halts all axes and spindles, letting maintenance personnel verify the brake holding state and cooling fans. Finally, SPOS=0 commands the spindle to execute a closed-loop angular orientation, testing the encoder pulse feedback stability.

Mitsubishi Diagnostic Program Block

G04 X1.0 ;
S1000 M03 ;
M19 ;

Dry Run Description: Executing this Mitsubishi test sequence begins with a G04 dwell of 1.0 second, during which speed loop parameters SV005 (VGN1) and SV008 (VIA) are monitored to detect static motor hunting or gear noise. The spindle then ramps up to 1000 rpm clockwise via S1000 M03, during which technicians check the load meter for fluctuations exceeding 120%. Finally, M19 commands a precise spindle orientation, validating the feedback tracking loops.

Error Analysis and Alarm Triggers

Brand	Alarm Code	Trigger Condition	Operator Symptom	Root Cause / Fix
Fanuc	SV0400	Servo motor or drive amplifier has overheated (detected via hardware thermostats or estimated values)	HMI shows OVERLOAD; axis halts immediately	Reduce cutting conditions or cutting depth; inspect mechanical axes for excessive load; check cabinet cooling fan
Fanuc	SV0411	Positional deviation during movement becomes larger than the mathematical limit set in Parameter 1828	Axis stops moving, throwing EXCESS ERROR MOVING alarm	Inspect mechanical guideways and ball screws for binds; check setting value of servo loop gain Parameter 1825
Fanuc	SV0438	Excess motor current flows in main circuit or inverter	Ready signal drops (VRDY OFF); drive disables and axis halts	Winding short-circuit or severed power cable; disconnect lines and test insulation resistance using a megohmmeter
Siemens	Alarm F7900 / 207900	Servo operates at torque limit for longer than 1 second and remains below 120 rpm threshold	Machining channel ceases; G-code execution stops immediately	Verify mechanical binds, carriage obstructions, and adjust SINAMICS torque limits and stall delay parameter p2178
Siemens	Alarm F7901 / 207901	Actual motor speed exceeds positive or negative speed limits set by parameter p1082 and tolerances	Axis halts, throwing OVERSPEED alarm	Check encoder feedback pulse count and verify speed limit parameters
Siemens	Alarm 207902	Motor has mechanically stalled for a duration longer than parameter p2178 delay time	Traversing axis locks out; channel execution ceases	Check physical obstruction in traversing range; adjust current limit parameter p0640
Mitsubishi	Alarm 31	Motor speed feedback exceeds allowable limits	Axis halts, HMI shows OVERSPEED	Adjust acceleration/deceleration time constant in parameters; inspect or repair the speed detector encoder
Mitsubishi	Alarm 46	Thermal protection function of the motor or detector activates	HMI displays thermal warning; active spindle or axis halts	Check heavy cutting load; inspect ambient temperature; clean or replace clogged cooling fans
Mitsubishi	Alarm 50	Overload detection level continuously exceeds 100% threshold	HMI displays OVERLOAD 1; axis disables immediately	Remedy mechanical binding, carriage alignment, or high cutting loads; keep power ON to allow fan cooling
Mitsubishi	Alarm 53	Positional deviation between actual and theoretical coordinates during servo OFF state exceeds parameter SV026	Vertical axis drops unexpectedly under its own weight	Adjust excessive error parameter SV026; inspect mechanical electromagnetic brake holding torque

Application Note for Machine Maintenance

Technicians attempting to recover from a phase-to-ground short circuit or current alarm like SV0438 must adhere to strict maintenance protocols. Never attempt to bypass a fault by cycling power or forcing active overload alarms (Alarm 50) clear. Doing so prevents internal drive cooling fans from running and runs the risk of permanently melting the motor windings. Instead, technicians must physically disconnect the power lines from the amplifier and use a megohmmeter to test the insulation resistance of the U, V, and W wires. When dealing with vertical axes, mechanical holding brakes must be secured prior to diagnostic detachment to prevent the axis from dropping under its own weight, which could lead to severe operator injury or a major machine collision.

During commissioning or repair cycles, technicians must verify all interlocking safety mechanisms, similar to checking safety loops during a standard door switch and limit switch inspection, ensuring all axis travel ranges are physically cleared before engaging closed-loop control.

Related Command Network

• G31 (Torque Limit Skip): Bypasses standard servo positioning based on high-speed digital sensor inputs, heavily interacting with position error parameters.
• G04 (Dwell): Pauses axis motion for a defined duration, allowing technicians to observe position deviation settling in a static stop state.
• LIMS (Spindle Speed Limitation): Cops the maximum spindle RPM in Siemens systems to protect chucks and vise jaws from extreme centrifugal forces.
• M19 (Spindle Orientation): Commands the spindle to stop at a precise angular position, testing the integration of spindle encoders and feedback control loops.

Conclusion

Preventative maintenance of CNC servo motors requires a structured balance of parameter tuning, seal inspection, and diagnostic interpretation. By monitoring position deviation registers on Fanuc, SINAMICS fault parameters on Siemens, and 7-segment hardware LED sequences on Mitsubishi, technicians can catch degraded bearings or insulation resistance failures before they escalate. Implementing regular cooling fan checks, verifying torque limit settings, and testing insulation resistance with a megohmmeter ensures long-term axis reliability and protects the entire machine tool drivetrain from catastrophic high-speed collisions.

Frequently Asked Questions

How do you safely troubleshoot a suspected phase-to-ground short circuit on a Fanuc servo motor?

When encountering a short-circuit alarm like SV0438, immediately stop operations and do not cycle the machine power. Disconnect the U, V, and W power wires directly from the servo amplifier terminals. Use a high-quality megohmmeter to measure the insulation resistance between each motor phase and the physical ground; if the reading is near zero, the winding insulation has been compromised by cutting fluid or thermal stress, requiring motor rebuilding or replacement before powering up the amplifier.

What is the correct procedure when a Siemens drive encounters Alarm F7900 Motor Blocked?

This alarm indicates that the controller has reached its torque limit for over one second while speed is under 120 rpm. First, physically inspect the traversing area for mechanical blocks, carriage interference, or severe turret binding. Next, navigate to the SINAMICS parameters on the HMI and inspect parameter r0949 to read the exact fault value; check if the current limit parameter p0640 is set too low to overcome initial guideway friction, and adjust the programmable stall delay time if executing heavy, slow-speed cutting.

Why must you keep the drive unit power ON when troubleshooting a Mitsubishi Alarm 50 overload?

A common mistake when Alarm 50 (Overload 1) occurs is cycling the drive power OFF and ON to clear the error. The practical consequence of this action is that the internal cooling fans shut down immediately, preventing heat dissipation from the active power modules and leading to permanent motor winding or drive amplifier failure. Instead, keep the main cabinet power ON to allow the internal fans to cool the amplifier, open the HMI NC Memory Diagnosis screen, and inspect speed loop gain SV005 (VGN1) and SV008 (VIA) values to check for machine resonance.