Yaskawa Servo Feedback Cable Problems: Signal Interference, Faults, and Diagnostic Methods

Why Your Yaskawa Servo Keeps Showing Encoder or Feedback Errors

If a Yaskawa servo system suddenly stops, triggers an encoder alarm, or behaves unpredictably during motion, the problem is often not the motor itself.

In many real cases, the issue comes from the feedback cable system, which is responsible for sending position data from the encoder back to the servo drive.

Typical situations users report:

• Robot suddenly stops during production
• Encoder alarm appears after running for a while
• System works normally after restart, but the issue comes back
• One axis behaves differently from others
• Position loss happens during fast movement

These symptoms usually point to a problem in the feedback signal path rather than a mechanical failure in the servo motor.

Common Symptoms of a Bad Servo Feedback Cable

Servo feedback issues rarely fail completely at once. Most problems start small and become intermittent.

Motion problems you may notice:

• Robot arm shakes slightly during movement
• Position accuracy slowly becomes worse
• Sudden jerks during acceleration or deceleration
• One axis feels unstable compared to others

System warnings and alarms:

• Encoder communication alarm (intermittent or permanent)
• Position deviation warning
• Random servo stop without clear reason
• Alarm disappears after restart but returns later

Behavior pattern that matters most:

• Works fine when idle, fails during motion
• Problem comes and goes randomly
• Worse when machine is running at high speed

This pattern is a strong indicator of a feedback signal issue.

Why Servo Feedback Cable Problems Happen

Most servo feedback cable failures come from real production conditions rather than sudden breakdowns.

Internal wire damage (most common)

Over time, the cable inside gets damaged even if the outer jacket looks fine:

• Repeated bending during robot movement
• Wire fatigue inside drag chains
• Small broken strands causing unstable contact

Electrical noise interference (EMI)

In industrial environments, electrical noise can affect signal quality:

• Power cables running too close to feedback lines
• Noise from inverters or servo drives
• Poor shielding performance over time

Connector contact problems

Sometimes the issue is not the cable itself but the connection point:

• Slight looseness in connectors
• Wear from repeated plugging/unplugging
• Oxidation increasing resistance
• Vibration causing momentary disconnects

Shielding or grounding issues

If shielding is damaged or grounding is unstable:

• Noise enters signal lines
• Encoder data becomes unstable
• System misreads position information

How to Check If the Feedback Cable Is the Problem

Before replacing major components, a few simple checks can help isolate the issue.

Step 1: Cable swap test (most effective method)

Replace the suspected feedback cable with a known good one.

• If the problem disappears → cable is the issue
• If the problem stays → check encoder or drive

This is the fastest way to confirm the root cause.

Step 2: Check when the fault happens

Observe when the problem appears:

• Only during movement → likely cable or noise issue
• Only at high speed → signal instability
• Random occurrence → connector or internal break

Step 3: Basic continuity check

Use a multimeter to check:

• Each signal line continuity
• Shield connection integrity
• Any intermittent open circuit

Even small interruptions can cause servo alarms.

Step 4: Inspect cable routing

Check the installation environment:

• Is the cable too close to power lines?
• Is it running near inverter or motor cables?
• Is there proper separation and shielding?

Step 5: Check connectors

Physically inspect:

• Loose locking mechanism
• Signs of wear or oxidation
• Movement or vibration at the connector point

Why Small Cable Issues Can Cause Serious Servo Alarms

Servo systems rely on continuous and accurate feedback from the encoder. Even very small disturbances in the signal can create large system reactions.

Signal distortion during transmission

When the signal becomes unstable:

• Position data becomes inaccurate
• The drive receives incorrect motion information
• Correction actions become unstable

Encoder data errors

If data packets are corrupted:

• Position jumps or drops
• System loses tracking accuracy
• Servo drive may trigger safety stop

Feedback loop instability

The servo system constantly corrects motion based on feedback.

When feedback is wrong:

• The system over-corrects
• Motion becomes unstable
• Vibration or sudden stops occur

Why the problem is often intermittent

Servo feedback issues are often not permanent because:

• Wires may reconnect during movement
• Noise only appears at certain speeds
• Connector contact changes with vibration

This is why the system can seem “normal” after a restart.

FAQ

Why does my Yaskawa servo alarm come and go?

This usually indicates an intermittent feedback issue caused by cable damage, connector contact problems, or signal noise.

Can a bad cable cause encoder alarms?

Yes. Even small signal interruptions can trigger encoder communication errors.

Why does the robot only fail during motion?

Movement introduces vibration, bending, and electrical noise, which exposes weak points in the cable or connectors.

How do I know if it’s the cable or the encoder?

The simplest method is a swap test. If the fault follows the cable, the cable is the issue.

What is the most common cause overall?

Internal wire fatigue combined with poor shielding or unstable connector contact.