5681 PU Communication Fault in ABB ACS880 Drive

5681 PU Communication in the ABB ACS880 Drive indicates that the drive has detected a communication failure between the Control Unit (BCU) and the Power Unit (PU). The ACS880 continuously exchanges status, control, protection, and diagnostic information between the control board and the power unit through an internal communication link. If this communication is interrupted, corrupted, or does not match the configured hardware settings, the drive generates Fault 5681 to prevent unsafe operation.

5681 PU Communication Fault in ABB ACS880 Drive


This fault may also occur when the control unit power supply configuration does not match Parameter 95.04 – Control Board Supply, causing the control unit to operate in an unexpected power mode.

Possible Causes

  • Incorrect setting of Parameter 95.04 – Control Board Supply.
  • Communication failure between the control unit (BCU) and the power unit.
  • Loose or damaged communication cable between the control unit and power unit.
  • Faulty connector on the control board or power unit.
  • Poor electrical contact in internal communication connectors.
  • Control unit powered incorrectly or with an unstable auxiliary supply.
  • Defective BCU (Bridge Control Unit).
  • Faulty power unit communication interface.
  • Internal communication bus failure.
  • Defective xINT interface board.
  • BAMU board not detected.
  • Parallel-connected module communication failure.
  • Communication link errors caused by electrical noise or interference.
  • Internal transmitter FIFO errors.
  • Firmware incompatibility between the control unit and power unit.
  • Hardware failure after replacement of the control board or power unit.
  • Internal PCB damage caused by electrical surge or aging components.

Solutions

  • Cycle power to the drive and verify whether the fault clears.
  • Verify the setting of Parameter 95.04 – Control Board Supply matches the actual control unit power configuration.
  • Inspect all communication cables between the control unit and the power unit.
  • Ensure all internal connectors are securely connected.
  • Check the control unit for proper auxiliary power supply.
  • Inspect communication connectors for bent pins or corrosion.
  • Verify the power unit is operating normally.
  • Check for damaged or loose internal wiring.
  • Review the auxiliary fault code to identify the exact communication error source.
  • Inspect the xINT interface board if the auxiliary code indicates it is missing.
  • Verify the BAMU board is correctly installed and functioning.
  • Update the drive firmware if recommended by ABB.
  • Replace defective communication cables or connectors.
  • Replace the faulty control board if communication hardware has failed.
  • Replace the power unit if its communication interface is defective.
  • Contact ABB technical support if the fault persists after hardware inspection.

Additional Information

The ABB ACS880 uses a high-speed internal communication link between the BCU (Bridge Control Unit) and the Power Unit (PU) to exchange operating commands, measurement data, status information, and protection signals.

If this communication is interrupted, the drive can no longer safely control the power electronics and immediately generates Fault 5681 to prevent unpredictable operation.

In addition to communication failures, this fault can also occur when the Control Board Supply configuration (Parameter 95.04) does not correspond to the actual hardware wiring. This mismatch prevents proper initialization and communication between the control unit and the power unit.

The drive provides an auxiliary fault code (format XXXY YYZZ) to help identify the exact source of the communication problem.

Auxiliary Code Interpretation

For parallel-connected power modules, the auxiliary code has the format XXXY YYZZ:

  • YYY – Identifies the affected BCU control unit channel.
    • 0 – Broadcast communication.
    • Other values identify the specific communication channel.
  • ZZ – Identifies the communication error source:
    • 01 – Transmitter side link error.
    • 02 – Transmitter side no communication.
    • 03 – Receiver side link error.
    • 04 – Receiver side no communication.
    • 05 – Transmitter FIFO error (see XXX).
    • 06 – xINT interface board not found.
    • 07 – BAMU board not found.
  • XXX – FIFO transmitter error code (used only when ZZ = 05):
    • 001 – Internal error (invalid call parameter).
    • 002 – Internal error (configuration not supported).
    • 003 – Transmission buffer full.

These auxiliary codes significantly simplify troubleshooting by identifying the exact location and type of communication failure.

Common Symptoms

  • Drive trips with Fault 5681.
  • Drive will not start.
  • Fault appears immediately after power-up.
  • Communication between the control unit and power unit is lost.
  • Drive remains in fault state after reset.
  • Control unit fails to detect the power unit.
  • Fault occurs after replacing the control board or power unit.
  • Fault appears intermittently due to loose communication connections.
  • Auxiliary communication error code is displayed.
  • Drive may stop unexpectedly during operation.

Recommended Troubleshooting Sequence

  1. Cycle power to the drive.
  2. Verify Parameter 95.04 – Control Board Supply.
  3. Check the control unit auxiliary power supply.
  4. Inspect communication cables between the control unit and power unit.
  5. Verify all internal connectors are securely connected.
  6. Inspect connectors for damaged pins or corrosion.
  7. Read and interpret the auxiliary fault code.
  8. Check the identified BCU communication channel (if applicable).
  9. Inspect the xINT interface board.
  10. Verify the BAMU board is installed correctly.
  11. Inspect the power unit communication interface.
  12. Update firmware if recommended by ABB.
  13. Replace defective communication hardware if necessary.
  14. Replace the control board or power unit if hardware failure is confirmed.
  15. Contact ABB technical support if the fault persists.

PU Communication Check Table

Check PointAction
Power cycleRestart the drive
Parameter 95.04Verify Control Board Supply setting
Control unit power supplyConfirm correct auxiliary power
Communication cableInspect for loose or damaged connections
Internal connectorsEnsure secure connections
Connector pinsCheck for bent pins or corrosion
Auxiliary fault codeIdentify communication error source
BCU communication channelVerify affected channel (parallel systems)
xINT boardVerify installation and operation
BAMU boardConfirm board is detected
Power unitInspect communication interface
FirmwareUpdate if recommended by ABB
Control boardReplace if communication hardware has failed
ABB technical supportContact if the fault remains after inspection

Preventive Maintenance Tips

  • Inspect internal communication connectors during scheduled maintenance.
  • Keep communication cables securely fastened and free from mechanical stress.
  • Verify Parameter 95.04 after commissioning or hardware replacement.
  • Protect the drive from electrical noise using proper grounding and shielding.
  • Inspect internal boards for signs of overheating or contamination.
  • Periodically check connector pins for corrosion or looseness.
  • Ensure stable auxiliary power to the control unit.
  • Update firmware according to ABB service recommendations.
  • Use only ABB-approved replacement boards and communication components.
  • Record recurring communication faults and auxiliary codes to assist long-term diagnostics.

Proper configuration of the Control Board Supply, secure communication connections between the control unit and power unit, careful interpretation of the auxiliary fault code, and routine inspection of the BCU, xINT board, BAMU board, and communication hardware will help prevent recurring 5681 PU Communication faults in ABB ACS880 drives, ensuring reliable internal communication, dependable drive operation, and long-term system availability.

Comments

Post a Comment

Popular posts from this blog

Allen Bradley Kinetix 5500 Drive Fault Codes List

Complete guide to Allen Bradley Kinetix 5500 fault codes. Troubleshoot FLT codes, Single-Cable (DSL) feedback errors, shared bus faults, and perform diagnostics via Studio 5000. Kinetix 5500 Fault Codes Reference Table Kinetix 5500 Fault Codes Reference Table Kinetix 5500 Fault Codes Reference Table Fault Code and Meaning Cause and Remedy FLT S03 – MTR OVERSPEED FL Motor Overspeed Factory Limit Fault Cause: Motor speed has exceeded 125% of its maximum speed. Remedy: Check control loop tuning. FLT S04 – MTR OVERSPEED UL Motor Overspeed User Limit Fault Cause: Motor speed has exceeded motor overspeed user limit. Remedy: Check control loop tuning. Increase the Motor Overspeed UL attribute value. FLT S05 – MTR OVERTEMP FL Motor Overtemperature Factory Limit Fault Cause: Calculations based ...
Read more

Danfoss VACON 100 FLOW Drive Fault Codes List

Access the complete reference guide for Danfoss VACON 100 FLOW drive fault codes. Learn to diagnose Multipump communication errors, dry run faults, and use Vacon Live software. VACON 100 FLOW Fault Codes Reference Table VACON 100 FLOW Faults and Alarms VACON 100 FLOW - Fault Tracing Fault Code and Meaning Cause and Remedy Fault Code 1, ID 1 Overcurrent (Hardware Fault) Cause: There is too high a current (> 4 × IH) in the motor cable. a sudden heavy load increase a short circuit in the motor cables the motor is not the correct type the parameter settings are not properly made Remedy: Check the loading. Check the motor. Check the cables and connections. Make an identification run. Set the acceleration time longer (P3.4.1.2 and P3.4.2.2). Fault Code 1, ID 2 Overcurrent (Software Fault...
Read more

ABB ACH580 Drive Fault Codes List

Access the complete reference guide for ABB ACH580 HVAC drive fault codes. Learn to diagnose issues via the Hand-Off-Auto panel, BACnet integration, and Fireman’s Override. The ABB ACH580 is the industry-standard flagship drive for HVACR applications. Designed to control air handling units, cooling towers, and chillers, it ensures critical comfort and safety in buildings. When a malfunction occurs, the dedicated Hand-Off-Auto (HOA) control panel displays a 4-digit code alongside plain-text diagnostics, often integrated directly into the Building Management System (BMS). This guide provides the most updated reference to help you interpret these codes and maintain building environmental standards. ACH580 Fault Codes Reference Table Use the search bar below or browse the table to identify your specific error code: ABB ACH580 Drive Fault Codes List ABB ACH580 Drive Fault Codes List Fault Code and Meaning Cause and Remedy A2B1...
Read more