FANUC SRVO-064 PHAL Alarm: Pulse Coder Phase Error Troubleshooting

When a FANUC robot displays SRVO-064 PHAL, the controller has detected an abnormal phase condition in the pulses generated by the Pulse Coder.

The Pulse Coder is part of the robot's position feedback system. It provides feedback signals that allow the controller to monitor motor position and movement.

If the controller detects an abnormal pulse phase, it may generate SRVO-064 and prevent normal servo operation.

However, there is an important detail when diagnosing this alarm: SRVO-064 may appear together with other Pulse Coder communication alarms, including DTERR, CRCERR, or STBERR. In these situations, the PHAL alarm may not represent an independent Pulse Coder phase failure.

This guide explains what FANUC SRVO-064 means, how to identify the affected axis, how to interpret related alarms, and when Pulse Coder replacement may be necessary.

1. What Does FANUC SRVO-064 PHAL Mean?

SRVO-064 – PHAL Alarm (Pulse Coder Phase Error)

According to FANUC controller maintenance documentation, this alarm occurs when the phase of the pulses generated in the Pulse Coder is abnormal.

The Pulse Coder is used to provide position feedback from the robot's servo motor to the controller.

The controller relies on this feedback to determine motor position and movement. When the pulse phase is detected as abnormal, the controller reports SRVO-064 for the affected axis.

The alarm message also identifies the relevant robot group and axis.

For example:

• Group: Identifies the robot or motion group.

• Axis: Identifies the affected axis within that group.

This information is important because it helps maintenance personnel locate the affected motor and its associated Pulse Coder.

What Is a Pulse Coder?

A FANUC Pulse Coder is a position feedback device associated with the servo motor.

Its main functions include:

• Generating position-related feedback signals.

• Providing motor position information to the controller.

• Supporting servo control and position monitoring.

• Enabling the controller to track motor movement.

A Pulse Coder problem can therefore affect the controller's ability to correctly interpret motor position.

Although the terms Pulse Coder and Encoder are sometimes used interchangeably in industrial automation discussions, use the exact component terminology and part number when identifying FANUC replacement parts.

2. Common Conditions Associated with SRVO-064

SRVO-064 specifically identifies an abnormal pulse phase condition. It should not automatically be treated as a generic encoder cable failure.

The following conditions are important when investigating the alarm.

2.1 Abnormal Pulse Coder Output

The most direct explanation is that the Pulse Coder is generating an abnormal pulse phase.

If the Pulse Coder itself is defective, the controller may be unable to receive valid position feedback.

The FANUC maintenance procedure for applicable controller generations lists replacement of the affected Pulse Coder as the corrective action.

2.2 Related Pulse Coder Communication Alarms

SRVO-064 may appear together with other Pulse Coder-related alarms.

FANUC documentation specifically notes that PHAL may accompany:

• SRVO-068 DTERR

• SRVO-069 CRCERR

• SRVO-070 STBERR

When these alarms occur together, the PHAL alarm may not represent an actual independent phase error.

This is an important diagnostic distinction.

Do not immediately replace the Pulse Coder based only on SRVO-064 without reviewing the complete alarm history and identifying any accompanying alarms.

2.3 Pulse Coder Feedback System Problem

If SRVO-064 remains active after the related alarm conditions have been investigated, the affected Pulse Coder requires further diagnosis.

The applicable FANUC maintenance procedure should be followed to determine whether the Pulse Coder needs replacement.

Do not assume that the servo amplifier, robot connection cable, or encoder cable is defective without supporting diagnostic evidence.

3. How to Troubleshoot FANUC SRVO-064 PHAL

A structured diagnostic process helps prevent unnecessary replacement of expensive servo components.

Step 1: Confirm the Alarm Code and Affected Axis

Open the FANUC alarm screen and record the complete SRVO-064 message.

Pay attention to:

• Alarm code: SRVO-064.

• Alarm description: PHAL.

• Group number.

• Axis number.

• Time when the alarm occurred.

The affected axis identifies which motor and Pulse Coder should be investigated.

Do not assume that the alarm affects the entire robot. It may be associated with one specific axis.

Step 2: Review the Complete Alarm History

Check whether other servo or Pulse Coder alarms appeared at the same time.

Pay particular attention to:

If SRVO-068, SRVO-069, or SRVO-070 appears together with SRVO-064, investigate the related communication alarm conditions first.

FANUC documentation warns that SRVO-064 may be generated as an accompanying alarm in these situations, even when no independent PHAL condition exists.

Step 3: Identify Whether the Alarm Is Persistent

Determine whether SRVO-064:

• Appears immediately when the controller starts.

• Occurs during robot operation.

• Appears together with other Pulse Coder alarms.

• Remains after the related alarm conditions have been addressed.

Record the conditions under which the alarm occurs.

Avoid repeatedly resetting the alarm without understanding why it is being generated.

Step 4: Inspect the Relevant Feedback System

Using the applicable FANUC maintenance procedure, inspect the feedback system associated with the affected axis.

Depending on the controller and robot configuration, qualified maintenance personnel may need to examine:

• The affected servo motor and Pulse Coder assembly.

• Relevant electrical connections.

• The robot connection cable and internal feedback wiring when indicated by related communication alarms.

• The servo amplifier interface where the applicable diagnostic procedure requires it.

Before inspecting or disconnecting electrical components, follow the required power isolation procedure and FANUC safety documentation.

Do not disconnect connectors while the equipment is energized.

Step 5: Determine Whether Pulse Coder Replacement Is Required

For SRVO-064, FANUC maintenance documentation lists replacement of the affected Pulse Coder as the corrective action.

If the alarm remains and the diagnostic procedure confirms a Pulse Coder fault, replacement may be required.

However, first distinguish a genuine PHAL condition from an accompanying alarm caused by DTERR, CRCERR, or STBERR.

This prevents replacing a Pulse Coder unnecessarily when the primary problem lies elsewhere in the feedback communication path.

Step 6: Follow the Required Post-Replacement Procedure

After replacing a Pulse Coder, follow the maintenance and setup procedures specified for the particular robot and controller.

Depending on the hardware configuration and the effect of the repair, position reference verification or mastering may be required.

Do not assume that the same post-replacement procedure applies to every FANUC robot model.

Before returning the robot to production, verify that:

• The replacement component is correct.

• The alarm has cleared.

• Position feedback is functioning correctly.

• Any required mastering or position verification has been completed.

• The robot passes the applicable operational and safety checks.

4. SRVO-064 vs. Other FANUC Pulse Coder Alarms

Several FANUC alarms involve the Pulse Coder, but they identify different problems.

Understanding these differences helps maintenance personnel select the correct diagnostic procedure.

These alarms should not be treated as interchangeable encoder faults.

For example:

• SRVO-062 and SRVO-065 are associated with Pulse Coder battery conditions.

• SRVO-064 identifies an abnormal pulse phase.

• SRVO-068, SRVO-069, and SRVO-070 concern Pulse Coder serial data communication or status.

The corrective action depends on the actual alarm and the applicable FANUC controller documentation.

5. Pulse Coder vs. Encoder Cable: Which Component Should You Check?

When an encoder-related alarm appears, it is easy to assume that the encoder cable is defective.

However, SRVO-064 specifically identifies an abnormal Pulse Coder pulse phase. It does not automatically confirm a cable failure.

The distinction is important when selecting replacement parts.

The exact component arrangement varies by FANUC robot and motor generation.

A Pulse Coder may be integrated into the servo motor assembly or supplied as a separately identifiable component, depending on the design.

Always verify the original part number and replacement configuration before ordering.

6. How to Identify the Correct FANUC Pulse Coder Replacement

If Pulse Coder replacement is required, selecting the correct part is essential.

A visually similar component may not be electrically or mechanically compatible with the original assembly.

Before sourcing a replacement, collect the following information.

6.1 Robot Model

Identify the complete FANUC robot model.

Different robot series and motor configurations may use different Pulse Coder assemblies.

6.2 Affected Axis

Record the axis number reported in the SRVO-064 alarm.

For example, an alarm affecting Axis 1 requires investigation of the feedback system associated with that axis.

Do not order a replacement based only on the robot model without confirming the affected motor and axis.

6.3 Servo Motor Model

Record the servo motor model or identification number.

This information helps identify the correct feedback component.

6.4 Original Pulse Coder Part Number

If available, record the complete Pulse Coder or motor assembly part number.

Include all suffixes and revision information.

If the Pulse Coder is integrated into the motor, provide the motor identification label instead.

6.5 Photos and Identification Labels

If the original part number is unclear, provide:

• Robot model identification.

• Servo motor nameplate.

• Pulse Coder label, if separately available.

• Connector photos.

• Complete SRVO-064 alarm message.

These details help verify the correct replacement component.

7. Replace the Pulse Coder or the Complete Servo Motor?

The replacement scope depends on the motor design and availability of compatible components.

Do not replace the complete servo motor or servo amplifier simply because SRVO-064 appears.

First confirm the affected component and the correct replacement configuration.

8. Frequently Asked Questions

What does FANUC SRVO-064 PHAL mean?

SRVO-064 PHAL indicates that the phase of the pulses generated in the Pulse Coder is abnormal.

The controller identifies the affected group and axis so maintenance personnel can investigate the corresponding feedback system.

Does SRVO-064 mean the Pulse Coder is defective?

It may indicate a genuine Pulse Coder phase fault. However, FANUC documentation notes that SRVO-064 can also appear together with SRVO-068 DTERR, SRVO-069 CRCERR, or SRVO-070 STBERR, even when no independent PHAL condition exists.

Review the complete alarm history before replacing the Pulse Coder.

Can an encoder cable cause SRVO-064?

SRVO-064 specifically identifies an abnormal Pulse Coder pulse phase, not a confirmed encoder cable failure.

If communication-related alarms appear at the same time, inspect the relevant feedback communication path according to the applicable maintenance procedure.

What is the difference between SRVO-064 and SRVO-068?

SRVO-064 identifies an abnormal Pulse Coder pulse phase.

SRVO-068 DTERR indicates that the serial Pulse Coder does not return serial data in response to a request signal.

They represent different alarm conditions and require separate diagnostic procedures.

Does replacing the Pulse Coder require robot mastering?

The required post-replacement procedure depends on the robot and Pulse Coder configuration.

Follow the applicable FANUC maintenance manual to determine whether mastering or position reference verification is required.

Can I replace only the Pulse Coder instead of the complete servo motor?

In some FANUC motor configurations, the Pulse Coder may be separately replaceable. In others, it may be integrated into the motor assembly.

Confirm the motor model, original part number, and replacement procedure before ordering.

Source FANUC Pulse Coder and Encoder Components

If your FANUC robot displays SRVO-064 PHAL, identifying the affected axis and confirming the actual Pulse Coder condition are the first steps toward a reliable repair.

InRobots supports sourcing FANUC robot feedback components and hard-to-find industrial robot spare parts.

To help identify the correct replacement, provide:

• FANUC robot model.
• Controller model.
• Complete SRVO-064 alarm message.
• Affected group and axis.
• Servo motor model.
• Original Pulse Coder or motor part number, if available.
• Photos of the motor identification label and component.
• Required quantity.

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You can also explore our FANUC robot spare parts for related replacement components.