🛠️ How to Reset an Allen-Bradley PLC (MicroLogix, CompactLogix, Contro

Whether you’re troubleshooting a solid red fault light or restoring a PLC to factory settings, knowing how to properly reset your Allen-Bradley controller can save valuable time and prevent unnecessary downtime. This guide breaks down four effective reset methods—along with when and how to use them.

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🧭 Quick Reset Method Selector

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🔍 1. When Should You Reset an Allen-Bradley PLC?

You may need to reset the PLC if:

• A solid red fault LED is on

• A major fault has occurred

• The PLC is unresponsive or stuck

• You’re about to reprogram and want to start clean

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🔄 2. Reset Methods Explained

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✅ Method 1: Power Cycle (Basic Reset)

Best for minor runtime issues or simple glitches.

Steps:

1. Turn OFF power to the PLC.

2. Wait 10–30 seconds to let capacitors fully discharge.

3. Turn power back ON.

4. Check LED indicators—if the issue was minor, the PLC should reboot normally.

💡 Tip: Keep this method as your first go-to before escalating to software or factory reset.

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🧑💻 Method 2: Reset via RSLogix 500 / Studio 5000

Used to clear major or recoverable faults using Allen-Bradley software.

Applies to:

• MicroLogix/SLC (use RSLogix 500)

• CompactLogix/ControlLogix (use Studio 5000)

Steps:

1. Connect to the PLC via Ethernet or serial.

2. Open RSLogix 500 or Studio 5000, then go online with the controller.

3. Navigate to:
   Controller Organizer > Controller > Properties > Faults

4. Click “Clear Faults”.

5. Change the controller mode to RUN or REMOTE RUN.

⚠️ Note: Always investigate the cause of the fault before clearing it to avoid repeat errors.

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🧼 Method 3: Factory Reset (Memory Clear / Hard Reset)

For unrecoverable errors, locked-up systems, or when wiping all data is required.

⚠️ Warning: This will erase your program and all memory. Ensure backups are made first.

Steps:

1. Turn OFF the PLC.

2. Locate the Memory Reset Switch (location varies by model—check your manual).

3. Hold the switch in the reset position.

4. While holding, turn the power ON.

5. Wait for the status LEDs to flash, then release the switch.

🧠 Use this if the PLC is non-responsive to software or hardware resets.

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🔑 Method 4: Key Switch Reset (For Keyed PLC Models)

Fast and effective method for resetting using the onboard key switch.

Applies to:

• ControlLogix

• Some CompactLogix models

Steps:

1. Turn the key to PROG (Program) mode.

2. Wait a few seconds for the controller to halt the program.

3. Turn the key to RUN mode.

4. Observe if the fault clears.

🛠️ Perfect for field resets when software access isn’t available.

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🧩 3. Additional Troubleshooting Tips

If a reset doesn’t resolve the issue, try these diagnostics:

• ✅ Check fault codes: Use software or onboard LEDs to identify specific errors.

• 🔌 Inspect I/O modules: Loose or malfunctioning I/O connections can trigger faults.

• 🧰 Update firmware: Using outdated controller firmware can cause reliability issues.

• 🔋 Check battery status: Some MicroLogix or SLC models require a working battery for memory retention.

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📚 Rockwell Support Resources

• 🔗 Studio 5000 Software & Firmware Downloads

• 🔗 MicroLogix Programming Guide (1766-L32BXB)

• 🔗 ControlLogix Controller Manual

• 🔗 Knowledgebase & Tech Support

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📝 Final Thoughts

Resetting an Allen-Bradley PLC doesn’t have to be complicated—just be sure to:

• 📦 Back up your program before doing memory resets.

• 🛑 Understand the fault cause before clearing it.

• 🧭 Use the correct method based on your PLC model and fault type.

Mastering these reset techniques empowers you to troubleshoot efficiently and minimize downtime across your automation systems.

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