Troubleshooting Tutorial: Common SLC 500 Faults – Part 3: I/O Faults

Allen-Bradley’s SLC 500 series, whether modular or fixed, includes robust self-diagnostic features. These features help detect issues across modules and report them using LED indicators and internal diagnostic codes. In this third part of our troubleshooting series, we will focus on I/O faults commonly encountered in the SLC 500 system.

Understanding I/O Error Codes

I/O errors reported by the CPU will include the specific slot number (in hexadecimal) and a fixed error code. For example, code xx50 indicates:

• xx = Hexadecimal slot number

• 50 = Chassis data error

1. Chassis Data Error (Error Code: xx50)

• Fault Type: I/O Errors

• Description: A chassis data error is detected

• Cause: Electrical noise, power surge, improper grounding, or intermittent power supply

• Resolution:

  • Re-download the program and set the CPU to RUN

  • Verify grounding integrity, install surge/noise suppression

  • Replace the chassis

Detailed Steps:

• Physically inspect and retighten ground screws

• Test surge protectors; install/replace as needed

• If needed, move the chassis to another enclosure

• Ensure replacement chassis matches part number to avoid full reconfiguration

2. Missing or Undetected Module (Error Code: xx52)

• Fault Type: I/O Errors

• Description: Required module is missing or removed

• Cause: Damaged or removed I/O module

• Resolution:

  • Reinstall/replace the module

  • Or disable the slot in Status file S:11 and S:12

Detailed Steps:

• Disconnect power before installing

• Align and slide the module until the tab locks

• Power up and check for status clearance

• To disable a slot:

  • Navigate to Data File Status > I/O tab

  • Change the slot value from 1 to 0 (e.g., slot 8)

3. Hardware Interrupt Problem (Error Code: xx5A)

• Fault Type: I/O Errors

• Description: Hardware interrupt or excessive noise

• Cause: For discrete I/O, likely noise; for specialty modules, consult user manual

• Resolution: Refer to the specific module’s documentation for recommended fixes

4. Module Inserted Under Power (Error Code: xx94)

• Fault Type: I/O Errors

• Description: Module inserted while powered, or self-reset occurred

• Cause: Hot-swap during RUN/TEST mode or module reset itself

• Resolution:

  • Remove module, clear fault, switch controller to RUN

  • Or reconfigure hardware definition and download the updated program

Detailed Steps:

• Power down and remove the module carefully

• Clear fault via RSLogix and return CPU to RUN

• To reconfigure:

  • Open RSLogix 500

  • Navigate to I/O configuration and drag new module into correct slot

  • Compile and download program

5. Battery Low Warning (Status Bit: S:5/11)

• Fault Type: Status

• Description: Battery Low LED is ON; S:5/11 set to 1

• Cause: Low battery charge

• Resolution: Replace battery (not a fault, but serious if ignored)

Battery Replacement for SLC 5/01 - 5/02:

• Do NOT remove power

• Open processor door, unplug old battery

• Clip in and connect new battery

Battery Replacement for SLC 5/03 - 5/05:

• Remove power and processor

• Replace battery on circuit board

• Reinstall processor and restore power

Final Notes I/O faults in the SLC 500 system often stem from hardware handling issues or electrical disturbances. By understanding error codes and following structured troubleshooting procedures, users can minimize downtime and avoid costly replacements. Stay tuned for more parts in this series covering additional fault categories.

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