What causes FANUC Robot alarm SRVO-025?

Internal servo calculation overflow during a complex motion. Robot configuration error causing extreme joint angle calculations. Singularity or near-singularity condition creating an extremely large joint command. Software bug or unexpected internal state. Path through or near a mechanical singularity.

How do I fix FANUC Robot alarm SRVO-025?

1. Perform a Cold Start: turn off the robot, then hold SHIFT+RESET on the teach pendant while powering on. 2. After cold start, test the motion path that caused the alarm at low speed. 3. If the alarm recurs, note the exact program and position and contact Fanuc technical support. 4. Check if the motion path passes near a singularity — modify the path if so.

FANUC Robot codes

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FANUC Robot Controller

Servo/Axis · Intermediate · 15-60 minutes

Alarm SRVO-025

Fanuc Robot SRVO-025 - Motn dt overflow

SRVO-025 Motn dt overflow occurs when the motion controller calculates a servo command that exceeds internal computational limits, typically during singularity transitions, extreme joint velocity calculations, or corrupted position data. This alarm represents a servo subsystem saturation condition where the calculated joint displacement or velocity command cannot be represented within the servo amplifier's numerical range. The error usually indicates either a path planning issue near kinematic singularities or corrupted internal motion state requiring a controller reset.

FANUC RobotServo/AxisIntermediate15-60 minutes

SRVO-025

Fanuc Robot SRVO-025 - Motn dt overflow

Motn dt overflow

The motion command issued to the servo system was too large. This internal error typically requires a cold start to recover. If it recurs, contact Fanuc technical support with a description of the conditions.

Root Cause Summary

Safety

Always verify robot is in a safe stopped state before entering the work envelope
Use T1 (low speed) mode when testing after clearing motion or servo alarms

Causes and Fixes

1
Perform Cold Start Recovery
Power off the controller completely. Hold SHIFT + RESET on the teach pendant while powering the controller back on. This clears the corrupted motion state and reinitializes the servo subsystem. Wait for full boot sequence and confirm all axes are ready.
Ensure robot is in a safe position before power cycle. All motion will stop and position may need re-reference.
2
Check Robot Configuration at Fault Position
Navigate to MENU > SYSTEM > Variables and check $SCR.$GENOVERRIDE to see system override state. Then go to MENU > ALARM > History (F5) > DETAIL and note the exact timestamp. Review the position register or taught point where alarm occurred. Check if joints 4, 5, or 6 were near 0° (wrist singularity) or if J2 and J3 were nearly aligned (shoulder singularity).
Press POSN on teach pendant and check Joint display. If J5 is near 0°±5°, you're at a wrist singularity. If the sum of J2+J3 is near 0° or 180°, you're at a shoulder/elbow singularity.
3
Verify Motion Termination Type
Review the program line that faulted. Check if motion uses FINE termination or CNT (continuous) termination. FINE terminations near singularities are more prone to overflow. Navigate to the program position and check for coordinate system: Joint moves (J) avoid singularities, while Linear (L) or Circular (C) moves through Cartesian space can trigger them.
Change critical LINEAR moves near singularities to JOINT moves. Edit the motion instruction from 'L P[X]' to 'J P[X]'. Joint moves calculate direct angular paths and bypass inverse kinematics singularities entirely.
4
Enable Singularity Avoidance
Go to MENU > SETUP > Frames > check the coordinate frame in use. Then navigate to MENU > SETUP > Config > Motion and verify parameter $SCR_GRP[1].$SING_CARE is set appropriately. Set to TRUE to enable singularity avoidance algorithms, though this may alter the tool path slightly near singularities.
Enabling singularity avoidance may change actual tool path near singular configurations. Re-verify application tolerances.
5
Modify Path with Intermediate Points
Add intermediate waypoints to guide the robot around the singularity region. Insert positions where wrist configuration is clearly defined (different NUT/NUB or FUT/FDB flags). Touch up positions ensuring J5 remains >15° away from 0° throughout the motion. Use MENU > UTILITIES > Controlled Start to test at 5% override.
Use the CONFIG display on POSN screen to verify: F U T N D B flags define wrist configuration. Add a point that forces a config change before the singularity rather than passing through it.

1
Perform Cold Start and Check Master Position
Execute cold start (SHIFT+RESET during power-on). After boot, go to MENU > SYSTEM > Master/Cal > Reset Master Image (F2) and verify 'Master Gage Unmatch' or similar warnings. If present, mastering may be corrupted. Check MENU > SYSTEM > Variables > $MASTER_ENB and $MASTER_DONE should both be TRUE.
Do not reset mastering without qualified mastering fixture or zero-reference marks. Incorrect mastering causes positional errors and potential collisions.
2
Verify Current Position Registers
With robot stationary, press POSN button on teach pendant. Verify all joint angles are within normal mechanical range (check robot mechanical unit manual for limits). Compare JOINT display values against WORLD and USER coordinate displays for consistency. Any NaN (not a number), extreme values (>999°), or flickering numbers indicate position data corruption.
Write down current JOINT position, then jog J1 by 1°, return to original position and verify JOINT values match exactly. Position encoder drift or corruption will show discrepancies.
3
Check Servo Encoder Alarms History
Navigate to MENU > ALARM > History and review all alarms in the log (use F3/F4 to scroll). Look for SRVO-001 (Pulse Not Ready), SRVO-062 (Serial encoder error), or SRVO-075 (Pulse coder alarms) that preceded the SRVO-025. These indicate encoder signal issues that corrupt position feedback.
Press F1 DETAIL on any encoder-related alarm to see which axis and timestamp. Cross-reference with the axis involved in the overflow motion.
4
Verify Robot Payload and Inertia Settings
Navigate to MENU > SETUP > Payload. Verify payload settings match actual tool weight and center of gravity. Incorrect payload can cause motion model mismatch leading to excessive commanded corrections. Check $PAYLOAD_GRP[1].$PAYLOAD[1-10] values. Also verify $INERTIA_GRP[1] parameters match tool specifications.
Incorrect payload settings can cause overshoot, oscillation, or servo errors during acceleration. Always configure payload accurately.

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