Sigma 1 - Axis Servo Motor and Cables - How it Works and Troubleshooting Guide

How it Works

The servo motors in Haas machines are closed-loop servomechanisms. They move and hold the axes in the positions requested by the program. Each servo motor has an embedded encoder unit which provides position and speed feedback to the control (Maincon or Mocon). The control uses the encoder feedback to ensure accuracy in executing a program.

Servo motors that are used on the Z axis in mills or the X Axis in lathes are equipped with an electromechanical brake to hold the axis in place. The brake engages automatically, and requires voltage from the I/O PCB to disengage.

Although there are different sized motors for specific applications, each motor has an ID plate to identify it.

The illustration shows a Yaskawa motor. The troubleshooting process for motors made by other manufacturers is the same.

Press POWER OFF. Set the main circuit breaker to the OFF position. Wait until the high voltage LED on the vector drive is completely off before disconnecting any cables.

Symptom Probable Cause Corrective Action Section

Alarm 161, 162, 163, 164 AXIS DRIVE FAULT.

Alarm 993 AMPLIFIER SHORT CIRCUIT

Faulty servo amplifier. Examine the corresponding amplifier assembly. 1
Faulty power cable. Inspect the cables and the connectors. 2
Faulty servo motor. Examine the corresponding servo motor. 3

Alarm 182, 183, 184, 185, 194, 278, 655-657, 680, 761, 763 AXIS CABLE FAULT.

Alarm 139, 140, 141, 142, 190, 273, 676, 685, 686, 687, 731, 732,733, 735 MOTOR Z FAULT.

Alarm 103, 104, 105 POSITIONING ERROR or Alarm 270, 709 SERVO ERROR TOO LARGE during a zero return.

Faulty encoder cable. Examine the cable and the connections. 4
Bad encoder connection at the motor encoder or at the Maincon (MOCON). Examine the connection at the motor and at the Maincon (MOCON). 5
Bad connection at the I/O PCB brake connectors. Examine the connection at the motor and at the I/O PCB 6

Section 1

Symptom: Alarm 161, 162, 163, 164 AXIS DRIVE FAULT.Alarm 993 AMPLIFIER SHORT CIRCUIT.

Probable Cause: Faulty servo amplifier.

Corrective Action:

Check the cables for a short: Make sure the axis servo motor cables are not contaminated or pinched. Contaminated or pinched cables can cause a short. Replace the cables if necessary.

Check the amplifier for a short. Power off the machine. Disconnect the cables for the axis servo motor at the amplifier that generates the alarm. Take the following resistance readings:

  • Terminal -HV to RED, WHT, and BLK terminals
  • Terminal +HV to RED, WHT, and BLK terminals

A short circuit in any of these measurements is an indication of a defective amplifier.

Go to Servo Amplifier - How it Works and Troubleshooting Guide to troubleshoot the amplifier.

Section 2

Symptom: Alarm 161, 162, 163, 164 AXIS DRIVE FAULT.Alarm 993 AMPLIFIER SHORT CIRCUIT.

Probable Cause: Faulty power cable.

Corrective Action:

Press POWER OFF. Set the main circuit breaker to the OFF position. Wait until the high voltage LED on the vector drive is completely off.

Examine the cables and connectors.

Make sure the cable connections at the corresponding amplifier are tight. Inspect the connector at the motor. Look for loose connections or contamination.

Examine the cable. Look for signs of damage or stiffness.

Disconnect the power cable from the amplifier and motor. Perform a resistance check from leg to leg, and from leg to ground. Make sure each reading results in a open connection. Check each leg from end-to-end for continuity. If there is an open connection, there is a problem with the cable.

Section 3

Symptom: Alarm 161, 162, 163, 164 AXIS DRIVE FAULT.Alarm 993 AMPLIFIER SHORT CIRCUIT.

Probable Cause: Faulty servo motor.

Corrective Action:

Examine the servo motor.

Make sure the motor’s connectors are not contaminated.

Disconnect and inspect the power cable connector at the motor. Make sure that there is no coolant contamination. Coolant contamination can cause this alarm and damage the amplifier. Measure the resistance from the pins labeled A, B and C at the motor connector to chassis ground.

  • The reading should be OPEN.
  • If there is not open resistance, the servo motor is at fault.

Section 4

Symptom: Alarm 182, 183, 184, 185, 194, 278, 655-657, 680, 761, 763 AXIS CABLE FAULT. Alarm 139, 140, 141, 142, 190, 273, 676, 685, 686, 687, 731, 732,733, 735 MOTOR Z FAULT. Alarm 103, 104, 105 POSITIONING ERROR or Alarm 270, 709 SERVO ERROR TOO LARGE during a zero return.

Probable Cause: Faulty encoder cable.

Corrective Action:

Power the machine off. Wait until the high voltage LED on the vector drive is completely off.

Examine the encoder cable. Look for stiffness and damage to the cable or the cable jacket. Go to diy.haascnc.com to troubleshoot the servo motor cables.

Section 5

Symptom: Alarm 182, 183, 184, 185, 194, 278, 655-657, 680, 761, 763 AXIS CABLE FAULT. Alarm 139, 140, 141, 142, 190, 273, 676, 685, 686, 687, 731, 732,733, 735 MOTOR Z FAULT. Alarm 103, 104, 105 POSITIONING ERROR or Alarm 270, 709 SERVO ERROR TOO LARGE during a zero return.

Probable Cause: Bad encoder connection at the motor or at the Maincon (MOCON).

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.

Perform a resistance check on the encoder cable from leg to leg, and from leg to ground. Make sure each reading results in a 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.

Section 6

Symptom: Alarm 182, 183, 184, 185, 194, 278, 655-657, 680, 761, 763 AXIS CABLE FAULT. Alarm 139, 140, 141, 142, 190, 273, 676, 685, 686, 687, 731, 732,733, 735 MOTOR Z FAULT. Alarm 103, 104, 105 POSITIONING ERROR or Alarm 270, 709 SERVO ERROR TOO LARGE during a zero return.

Probable Cause: Bad connection at the I/O PCB brake connectors.

Corrective Action:

Examine the connection at the I/O PCB connectors P79 or P78 [1]. Reseat the connection.

Use needle tip probes to measure the voltage across the red and black cables.

Press EMERGENCY STOP. There should be no voltage.

Press RESET to clear the alarms. The voltage should be between 20-30 VDC.

Examine the connection at the motor's brake [2] and power connectors [3] for contamination. Reseat the connections.

If no voltage is present, go to I/O PCB - How it Works and Troubleshooting Guide (Classic Haas Control) to troubleshoot the I/O PCB.

Be aware: Many service and repair procedures should be done only by authorized personnel. The service technicians at your Haas Factory Outlet (HFO) have the training, experience, and are certified to do these tasks safely and correctly. You should not do machine repair or service procedures unless you are qualified and knowledgeable about the processes.

Danger: Some service procedures can be dangerous or life-threatening. DO NOT attempt a procedure that you do not completely understand. Contact your Haas Factory Outlet (HFO) and schedule a service technician visit if you have any doubts about doing a procedure.

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