Service Home Spindle Encoder - Troubleshooting Guide - CHC - TG0134
Last updated: 10/15/2025

Spindle Encoder - Troubleshooting Guide - CHC

TG0134

Introduction

Encoders are used on Haas Machines to give feedback to the control about the direction and speed of the spindle. A Haas machine will alarm if any of the encoder signals are lost or are not responding to machine inputs. If the encoder is not generating an alarm it does not usually need to be replaced. Use this guide to troubleshoot spindle encoder related symptoms and alarms.

Haas machines use these types of encoders.

  1. Optical Encoder (Shafted)
  2. Magnetic Encoder (Hubbed, Shafted)
  3. Non-Contact Encoders

Non-Contact Encoder Troubleshooting

Symptom Table

Symptom / Alarms Possible Cause Corrective Action

The Spindle Motor Does Not Turn, and The Load Meter Stays at Maximum.

 The Wye-Delta contactors are not operating correctly. Command a spindle speed of 50 RPM, make sure the Wye contactor engages, if not refer to the Wye-Delta Contactor - Troubleshooting Guide - CHC
The Spindle Turns at The Low RPM and The Load Meter Stays Near The Maximum The non-contact encoder read head is not aligned correctly.

Check the non-contact encoder alignment.

For non-contact encoder alignment procedures refer to:

Alarm 237 SPINDLE SPEED ERROR


During Spindle Orientation the Spindle Will Not Orient Consistently in the Same Position.

 

The encoder belt or pulleys are worn.

 Check for worn encoder belt and pulleys. See the Belt and Pulley Inspection section below.
The non-contact encoder read head is not aligned correctly. Check the non-contact encoder alignment.

For non-contact encoder alignment procedures refer to:

 
A loose connection at the WYE-DELTA contactors or spindle motor wiring. Refer to the: Wye-Delta Contactor - Troubleshooting Guide - CHC
Optical, Magnetic Encoders

Alarm 173 SP–AXIS ZERO CHANNEL MISSING

Alarm 234 SPINDLE CABLE FAULT

 Loose encoder cable connection. The encoder cable is damaged. Check the encoder cable and connection. See the Main Processor/Encoder Cable section below.
Optical, Magnetic Encoders

Alarm 235 SPINDLE Z FAULT after replacing an optical encoder with a magnetic encoder and running a rigid tap cycle.

 The parameters for the magnetic encoder are not correct. Refer to the Magnetic Encoder - Shafted - Installation Aid reference document to make sure the parameters are correct.
Optical, Magnetic Encoders

Alarm 235 SPINDLE Z FAULT

 Loose encoder cable connection. The encoder cable is damaged. Check the encoder cable and connection. See the Encoder Signal Inspection section below.
The spindle encoder is defective. Classic Haas Control: If the machine is equipped with the Spindle Orientation Option
  1. command an M19 in MDI
  2. look at your INPUTS2 page for SPINDLE Z CHANNEL; you should see the bit change quickly from 0 to 1 and back to zero.
    • This indicates a Z pulse is being recognized
    • If no change then the encoder is defective, or the cable going to the encoder is open.

Main Processor/Encoder Cable

Corrective Action:

Examine the connector [1] on the Maincon or MOCON PCB. Make sure it is not damaged.

Examine the cable. Look for signs of damage or stiffness. The connector [4] has two housings [2,3] for the cable pins.

Measure the resistance on the encoder cable from leg to leg, and from leg to ground. Make sure each measurement results in an open connection.

Make sure the cable is firmly connected at both ends. Reseat both connections. Make sure the cable is installed in the correct connector at the Maincon or MOCON PCB.

Encoder Signal Inspection

Corrective Action:

  • Push [EMERGENCY STOP]
  • Rotate the spindle by hand and check SPINDLE SPEED for the RPM feedback.
  • Make sure the encoder and encoder cables are correctly connected to the Maincon / Mocon PCB.
  • Examine the cables and Maincon / Mocon PCB connections for damage. Replace as needed.

Belt and Pulley Inspection

Corrective Action:

  • Examine the encoder belts [1] for damage.
  • If the encoder belts are damaged replace them. Check for worn or loose pulleys [2].

 Note: For Mills Only. Once the encoder belts are replaced and tight, set PARAMETER 257 to set the correct position for a tool change.

Non-Contact Encoder Read Head Grounding

Read Head and Casting

  1. Disconnect the cable from the encoder read head.
  2. Use a multimeter and check the continuity between the read-head screw and the casting.
  3. If there is little or no continuity:
  • make sure the grounding cable to the spindle head casting is secured.
  • make sure the mounting screws are making contact with bare metal and not the anodized layer.

Connector Case and Read Head

  1. Check the continuity between the read head connector case [2] and the read head [1].
  2. If there is little or no continuity:
  • remove the jamnut from the M8 connector and install an M8 internal star washer onto the connector.
  • install and tighten the jamnut over the M8 star washer and install the read-head back onto the mounting bracket.

Encoder Ring to Read Head Alignment

Proper alignment of the read head to the encoder ring is critical.  The alignment will vary based on the brand of encoder.  Use the chart provided to make sure the encoder ring and read head are properly aligned.

VENDOR                               RLS                                    BAUMER

A                              0.020" +0.020 / -0.039                 0.0453" +/- 0.019

B                              0.0118" +0.0079 / -0.0039           0.0118" +/- 0.0039

C                                           0.362"                                      .0360"

 

 

 

Incorrect installation of the spindle may axially misalign the motor shaft.  Measure the distance from the top of the motor shaft to the top of the motor cooling fins.  It should be 1.291 ± .005.

If the shaft is axially misaligned the spindle motor must be replaced.

Encoder Ring to Read Head Alignment

Proper alignment of the read head to the encoder ring is critical.  The alignment will vary based on the brand of encoder.  Use the chart provided to make sure the encoder ring and read head are properly aligned.

VENDOR                               RLS                                    BAUMER

A                              0.020" +0.020 / -0.039                 0.0453" +/- 0.019

B                              0.0118" +0.0079 / -0.0039           0.0118" +/- 0.0039

C                                           0.362"                                      .0360"

 

 

 

Incorrect installation of the spindle may axially misalign the motor shaft.  Measure the distance from the top of the motor shaft to the top of the motor cooling fins.  It should be 1.291 ± .005.

If the shaft is axially misaligned the spindle motor must be replaced.

Electrical Diagrams