Fanuc Roboshot Alarm SV0300: Servo Amplifier Overload - Troubleshooting Guide
Published: 2026-05-31
Fanuc Roboshot Alarm SV0300 is a Fanuc CNC-level servo alarm (not a machine-level PLC alarm) generated by the Fanuc αi series servo amplifier when it detects an overload condition on one of the machine's servo axes. The Roboshot all-electric...
Fanuc Roboshot Alarm SV0300 is a Fanuc CNC-level servo alarm (not a machine-level PLC alarm) generated by the Fanuc αi series servo amplifier when it detects an overload condition on one of the machine's servo axes. The Roboshot all-electric injection molding machine uses Fanuc servo motors and amplifiers for all three primary axes: injection (including plasticating rotation), clamp (toggle mechanism), and ejector. An SV0300 alarm means the servo amplifier's current monitoring circuit has detected that the motor is drawing current exceeding the amplifier's continuous or peak rating for longer than the allowed duration.
The Fanuc servo amplifier monitors motor current via Hall-effect sensors on each phase and calculates the thermal load (I²t integral) in real time. When the thermal load exceeds the amplifier's protection curve, SV0300 is triggered and the amplifier disables motor excitation—the motor freewheels to a stop. The alarm message on the Fanuc LCD will specify which axis triggered the fault (e.g., 'SV0300 X (INJ)'), which is essential for isolating the root cause. Unlike hydraulic machines where an overload simply stalls the actuator, an all-electric machine's servo amplifier will trip to protect the power electronics from thermal damage.
Common root causes by axis: (1) Injection axis—excessive back pressure during plasticating, polymer frozen in barrel attempting cold start, or check ring jammed causing injection overload. (2) Clamp axis—toggle mechanism binding due to lack of lubrication on the toggle pins/bushings, misaligned tie-bar nuts creating uneven load distribution, or attempting to close on an obstruction (similar to Netstal Alarm 301 but detected electrically rather than hydraulically). (3) Ejector axis—stuck part or insufficient draft angle causing excessive ejection force.
Alarm Details
| Alarm Code | SV0300 |
|---|---|
| Brand / Machine | Fanuc Roboshot |
| Severity | Critical (Emergency Stop) |
| Component | Servo Amplifier / Servo Motor |
| Affected Systems | Injection Axis / Clamp Axis / Ejector Axis |
Troubleshooting Protocol
Identify which zone/component triggered the alarm. Record the error code, timestamp, and any measured deviation values shown on the diagnostic screen.
Power down the machine and follow Lock-Out Tag-Out procedures. Visually inspect the affected component for physical damage, loose connections, polymer leakage, or carbonized material.
Using a multimeter, check resistance/continuity on the affected circuit. Verify SSR functionality and fuse integrity. Compare readings to OEM specifications.
Replace the failed component with an OEM-approved part. Do not substitute with generic equivalents unless validated for the specific machine model and operating conditions.
Restart the machine, verify the alarm is cleared, run a test cycle, and document the root cause, repair performed, and parts replaced in the machine maintenance log.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Sumitomo Demag Servo Alarm | |
| Arburg Servo Drive Fault |
Frequently Asked Questions
How do I identify which axis triggered the SV0300 alarm and what to check first?
The Fanuc LCD display will show the axis identifier: 'SV0300 X' = X-axis (injection), 'SV0300 Y' = Y-axis (clamp), 'SV0300 Z' = Z-axis (ejector). For injection axis overload: check that the barrel is at full operating temperature before attempting screw rotation—never rotate the screw in a cold barrel with solidified polymer, which is the #1 cause of injection axis SV0300 on Roboshot machines. For clamp axis: inspect the toggle mechanism lubrication system. Roboshot toggle machines have automatic grease lubrication to the toggle pins; a clogged grease line or empty reservoir starves the pins and dramatically increases clamp motor torque demand. For any axis: after an SV0300 trip, the servo amplifier requires a reset (power cycle the machine control) and the axis must be manually moved off the obstruction before restarting automatic operation.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org