Troubleshooting SRVO-068 DTERR Alarm (J4 Axis) on NexBot LA013-001 Robot Arm

Related Products

Tools Required

• Lockout/Tagout (LOTO) Kit
• Insulated Phillips and Flathead Screwdrivers
• Digital Multimeter with continuity test function
• Hex Key Set (Metric)
• Personal Protective Equipment (PPE): Safety Glasses, Insulated Gloves

Article

This article provides troubleshooting procedures for the SRVO-068 DTERR alarm specifically related to the J4 axis on the NexBot Robotics LA013-001 6-Axis Robot Arm. This alarm indicates a loss of communication or data corruption between the main robot controller and the servo amplifier for the specified axis. Adherence to all site-specific safety protocols, including Lockout/Tagout (LOTO), is mandatory before performing any of these steps.

Symptom

The primary symptom is the immediate cessation of robot motion, accompanied by the following indicators:

• The teach pendant displays the alarm: SRVO-068 DTERR Alarm (G:1 A:4), indicating Group 1, Axis 4.
• The robot's brakes engage audibly.
• The J4 axis may go limp if the fault occurs while brakes are released, or it may be held by the brake.
• The fault light on the corresponding servo amplifier in the control cabinet may be illuminated.

Cause

The SRVO-068 alarm is typically caused by an interruption in the high-speed serial communication link. Common root causes include:

1. Cabling Issue: The robot's internal harness or the encoder feedback cable (SKU: NXB-SRV-ACE-025-A) is disconnected, damaged, or has a poor connection at either the motor or the amplifier.
2. Faulty Servo Amplifier: The servo amplifier responsible for the J4 axis (related to SKU: NXB-SRV-PWR511-001) has failed.
3. Electrical Noise: Significant electromagnetic interference (EMI) is disrupting the communication signal. This is often caused by improper grounding or shielding, especially if new equipment was recently installed near the robot cell.
4. Motor Encoder Failure: The encoder within the J4 axis motor has failed.
5. Controller Hardware Issue: In rare cases, the backplane or main CPU of the robot controller may have a fault.

Resolution Steps

Warning: These procedures involve exposure to hazardous voltages (400-480VAC). Only qualified maintenance personnel should perform these steps. Ensure a full LOTO procedure is completed before opening the controller cabinet.

Step 1: Power Cycle and Fault Reset

1. Attempt to clear the fault from the teach pendant.
2. If the fault does not clear, perform a full power cycle of the robot controller. Turn the main disconnect off, wait at least 60 seconds for capacitors to discharge, and then turn it back on.
3. If the alarm reappears immediately on startup, proceed to the hardware checks.

Step 2: Inspect External and Internal Cabling

1. With the controller powered down and locked out, perform a thorough visual inspection of the robot harness. Look for signs of pinching, abrasion, or acute bends, particularly around the J3 and J4 axes where flexing is most pronounced.
2. Open the robot controller cabinet.
3. Locate the servo amplifier for the J4 axis. It will be labeled accordingly on the amplifier rack.
4. Firmly reseat the encoder feedback cable connector (typically labeled 'CN2' or 'ENC') on the J4 amplifier.
5. Trace this cable back and ensure it is securely connected at any intermediate connection points and at the robot base.

Step 3: Isolate the Faulty Component (Amplifier vs. Cable/Motor) This step involves swapping components between the faulty axis (J4) and a known-working adjacent axis (e.g., J5) to determine the point of failure. This is an advanced diagnostic step.

1. Ensure the controller is locked out. Mark the cables and amplifier positions for J4 and J5 clearly before disconnecting anything.
2. Disconnect the encoder and power cables from the J4 and J5 amplifiers.
3. Carefully unseat both the J4 and J5 servo amplifiers (related to SKU: NXB-SRV-PWR511-001) from the backplane.
4. Swap their physical positions: install the amplifier from J4 into the J5 slot and the amplifier from J5 into the J4 slot.
5. Reconnect the cables to their original axes. The J4 cables connect to the amplifier now in the J4 slot (which was originally the J5 amplifier). The J5 cables connect to the amplifier now in the J5 slot (which was originally the J4 amplifier).
6. Remove the LOTO and power on the controller. Observe the alarm on the teach pendant.

• If the alarm is now SRVO-068 DTERR Alarm (G:1 A:5): The fault has moved to the J5 axis. This indicates the original J4 servo amplifier is faulty and must be replaced. Order replacement part NXB-SRV-PWR511-001.
• If the alarm remains SRVO-068 DTERR Alarm (G:1 A:4): The fault did not move with the amplifier. This strongly suggests the issue lies with the J4 encoder cable (NXB-SRV-ACE-025-A), the J4 motor's internal encoder, or the robot's internal harness.

Step 4: Further Cable and Motor Diagnostics If the fault points to the cable or motor:

1. Perform a continuity and pin-to-pin check on the encoder cable (NXB-SRV-ACE-025-A) using a multimeter. Compare readings to the robot's maintenance manual wiring diagram.
2. If the cable tests good, the failure is most likely the J4 motor's internal encoder. Motor replacement is typically required in this scenario.

Prevention

• Ensure all robot cabling has proper strain relief and is routed according to the NexBot Robotics LA013-001 installation manual to prevent premature wear.
• During routine preventative maintenance, visually inspect all harnesses for signs of damage.
• Verify that the control cabinet is properly grounded and that all cable shields are terminated correctly to mitigate EMI.
• Avoid routing high-power cables (e.g., from welders) parallel to robot communication cables.

Keywords