Sigma-5 servo motors, non-contact encoders output serial data signal to the control. If the serial data signal is missing or becomes unreliable the control will generate a serial data communication error. Electrical noise can cause the serial data signal from the encoder to become unreliable and cause false alarms. Follow the troubleshooting guide below to help eliminate the noise in the system.

1. Incorrect machine grounding. Make sure the ground wire size is correct. Also the ground wire should run all the way back to the electrical panel.
2. Noise from other equipment. Make sure the machine does not share it's electrical service with another machine.
3. Loose encoder data connectors at PCB or at the motor encoder, can cause the serial data to become unreliable. Refer to the Main Processor / Encoder Cable section.
4. Loose ground or high voltage power connectors will induce noise into the system.
   • electrical cabinet check for loose connection at all the ground and high voltage power terminals (vector drive, wye-delta contactors, transformer..etc).
   • pendant check for loose terminal connectors.
   • spindle head check for loose ground and motor power terminals.
5. The ferrite filters suppress high frequency noise produced by the amplifiers and vector drive, when servos are on. Make sure they are installed in:
   • Encoder data cables. Make sure there is a ferrite filter P/N 64 1252 installed in all the encoder data cables.
   • Axis motor power cables. Make sure there is a ferrite filter P/N 64-1252 installed in X, Y, Z axis motor power cables [1].
   • Spindle motor cables. Make sure there is a ferrite filter installed in the motor output of the vector drive.

     For a 40HP vector with 6 wire leads [1] use ferrite P/N 64-1254.

     For a 40HP vector with 3 wire leads [2] use ferrite P/N 64-1252.

     For a 20HP vector drive with 6 or 3 wire leads [3, 4] use ferrite P/N 64-1252.

6. Cable routing. Make sure that the encoder cable is separated from high power spindle/axis/pump cables.

Corrective Action:

Examine the connector [1] on the Maincon. 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.

If the pins have been pushed into the motor, you must replace the motor and cable together.

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.

Look for signs of damage and stiffness on the cable and connector. Disconnect the power cable from the amplifier and motor. Measure the resistance from leg to leg (red, white, black wires), and from leg to ground (green/yellow wire). Make sure the measurements result in an open connection. Refer to the table below as a reference. 

NOTE: If the machine is experiencing intermittent short circuit alarms move the axis to the location where the cable would be most bent before performing this test. This may improve the likeliness of finding an intermittent  short.

Perform a continuity test between the ground wire and the braided shield. If it fails the continuity test fails the cable shield is compromised. 

NOTE: If the machine is experiencing intermittent short circuit alarms move the axis to the location where the cable would be most bent before performing this test. This may improve the likeliness of finding an intermittent  short.

Check each leg from one end of the cable to the corresponding leg on the other end of the cable for continuity. Refer to the table above for wiring reference. If there is an open connection, there is a problem with the cable. 

NOTE: If the machine is experiencing intermittent short circuit alarms move the axis to the location where the cable would be most bent before performing this test. This may improve the likeliness of finding an intermittent  short.

Use the following troubleshooting chart to determine whether the motor, amp, or cable is defective.

When Alarm 993 SHORT CIRCUIT occurs disconnect the axis power cable from the motor. Press [RESET] and jog the axis.

If Alarm 103 AXIS SERVO ERROR TOO LARGE occurs then the motor is defective. If another Alarm 993 SHORT CIRCUIT occurs then the cable or amp is defective.

To determine if the cable or amp is defective disconnect the axis power cable from the motor and amp. Press [RESET] and jog the axis.

If Alarm 993 SHORT CIRCUIT generates then the amplifier is defective. If Alarm 103 AXIS SERVO ERROR TOO LARGE generates the cable is defective. 

Corrective Action:

Disconnect and inspect the power cable at the motor side. Verify the motor connectors are not contaminated, coolant contamination can generate drive fault alarms and damage the amplifier. Verify that the cable is connected to the corresponding amplifier as well. 

Measure the resistance from the pins Labeled A, B, and C at the motor connector to the chassis ground.

• The reading must show an open circuit 
• If the reading does not show an open ciruit, the motor is at fault

Conduct a continuity test from the ground pin and chassis ground. The multimeter should beep or read less than 1 ohm resistance for continuity, otherwise then there is a short in the motor. Measure the resistance between the pins labeled A, B and C, refere to the table below for the resistance values.

NOTE: Nominal winding resistance has been added to the table for the 4-wire test method, when using a multimeter use the typical resistance value column for the expected values.

Corrective Action:

Reseat the the connection for connectors P3, P4, or P5 on the I/O PCB.

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, refer to:

• Next Generation Control - I/O PCB -Troubleshooting Guide