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FANUC SRVO-068 Alarm : Causes, Troubleshooting & Encoder Cable Fix
FANUC SRVO-068 Alarm (Pulse Coder Alarm) is a common FANUC robot fault that appears when the controller loses stable position feedback from the servo motor encoder system.
Typical symptoms include sudden robot stops, axis movement failure, intermittent alarms during motion, or alarms that disappear after restart and return later.
Because SRVO-068 directly affects robot positioning and motion control, identifying the root cause quickly is important for reducing production downtime.
What Does FANUC SRVO-068 Alarm Mean?
SRVO-068 occurs when the controller cannot properly read the signal from the pulse coder (encoder). Since the robot relies on encoder feedback for precise positioning, any signal interruption will trigger this alarm.
How SRVO-068 Is Triggered
Robot motion depends on continuous feedback from the pulse coder (encoder). During operation:
- Encoder measures motor position
- Signals travel through the encoder cable
- Servo amplifier processes feedback data
- Controller verifies motion position
If signal transmission becomes unstable or interrupted, the controller detects inconsistent feedback and generates SRVO-068.
Common Symptoms in Real Applications
- Robot stops suddenly during operation
- Specific axis cannot move or respond
- Alarm appears intermittently, especially during motion
- System works after restart but fails again later
If the issue is intermittent, it is often a strong indication of cable-related problems rather than a complete hardware failure.
SRVO-068 Symptoms and Possible Causes
| Observed Symptom | Possible Cause |
|---|---|
| Alarm appears only during robot movement | Internal encoder cable fatigue or conductor breakage |
| Alarm appears immediately after startup | Loose connector or unstable feedback hardware |
| Only one robot axis is affected | Axis-specific encoder or cable issue |
| Alarm disappears after restart and returns later | Intermittent cable connection problem |
| Alarm remains after cable replacement | Servo amplifier or control hardware issue |
Observed behavior often provides useful diagnostic clues before replacing components. In many maintenance situations, the alarm pattern itself helps narrow down the probable source of the problem.
Main Causes of SRVO-068 Alarm
1. Damaged Encoder Cable (Frequently Seen in Field Maintenance)
In field maintenance environments, encoder cable fatigue is frequently observed because robot movement repeatedly bends and stresses the cable assembly.
2. Loose or Corroded Connectors
Connector issues can interrupt signal transmission between the encoder and controller, triggering unstable feedback signals.
3. Faulty Pulse Coder (Encoder)
If the encoder itself fails, the controller cannot receive accurate position data.
4. Servo Amplifier or Control Board Issues
Although less common, internal faults in the servo amplifier or control board can also cause feedback errors.
Step-by-Step Troubleshooting Guide
Step 1: Identify Alarm Behavior Pattern
- Appears immediately after startup
- Appears only during robot movement
- Occurs randomly during production
- Occurs on a specific axis only
The alarm pattern often narrows down the source before hardware replacement begins.
Step 2: Perform a Visual Inspection
Check the encoder cable for visible wear, bending damage, or loose connections. Pay close attention to areas near joints where movement is frequent.
Step 3: Check Connectors
Disconnect and reconnect all encoder-related connectors. Ensure there is no corrosion or contamination.
Step 4: Test for Intermittent Cable Failure
Move the robot slowly while monitoring the alarm. If the alarm appears only during movement, the cable is very likely damaged internally.
Step 5: Swap Test (If Available)
If possible, replace the encoder cable with a known working one. If the alarm disappears, the cable is confirmed faulty.
Step 6: Check Servo Amplifier
If the problem persists after cable replacement, inspect the servo amplifier and related hardware.
Components Commonly Inspected During SRVO-068 Diagnosis
The following components are frequently inspected during SRVO-068 diagnosis because they directly affect feedback signal transmission and position verification.
- FANUC Encoder Cable
- Robot Body Cable
- Servo feedback components
Check Compatible Encoder Cables →
Repair vs Replacement: What Should You Do?
While temporary fixes such as reconnecting cables may work, they are usually not reliable for long-term operation.
- Replace the cable if the issue is intermittent
- Replace the encoder if no signal is detected at all
- Inspect amplifier if problem persists after replacement
In industrial environments, replacing faulty components is typically more cost-effective than repeated troubleshooting downtime.
Real-World Insight
In many maintenance cases, SRVO-068 is not caused by complete cable breakage, but by internal conductor fatigue.
This behavior often occurs because conductor strands inside the cable temporarily reconnect and disconnect as the robot changes position.
As a result, the robot may operate normally at one position but trigger SRVO-068 when the cable bends during movement.
This is why cable replacement is often recommended even if no external damage is visible.
Related FANUC Alarm Guides
- FANUC SRVO-050 Collision Detect Alarm
- FANUC SRVO-062 Pulse Mismatch Alarm
- FANUC SV044 Servo Amplifier Alarm
FAQ
Can a damaged encoder cable trigger intermittent SRVO-068 alarms?
Yes. Internal conductor fatigue may temporarily reconnect and disconnect as the robot moves.
Can I continue running the robot with SRVO-068?
Continued operation is generally not recommended because unstable feedback can affect positioning accuracy.
Does SRVO-068 always mean encoder failure?
No. Cable degradation and connector problems are frequently encountered in field service situations.
How can I identify which axis is causing SRVO-068?
The alarm details page on the controller usually indicates the affected axis. Repeated alarms on the same axis often suggest a localized cable or encoder issue.
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