1769 CompactLogix Fault Major Fault Type 1 — Power-Up Default Fault

Overview

The Allen-Bradley 1769 CompactLogix Major Fault Type 1 (Power-Up Default Fault) indicates that the controller lost its running application program during a power cycle or reset sequence. This fault occurs when the CPU registers a cleared or corrupted volatile memory (RAM) state upon booting up, prompting it to either enter a completely wiped out-of-box condition or load a backup image from non-volatile memory (SD Card or CompactFlash).

When this fault occurs, the PLC cannot enter Run mode. This is most commonly caused by a flat RAM-backup battery, a failing internal holding capacitor, severe power supply sag during shutdown, or system bus errors that interrupt the proper power-down save sequence.

Symptoms

When a 1769 CompactLogix processor suffers a Type 1 Power-Up Default Fault, you will observe several distinct visual and software indicators:

• I/O LED is OFF or Flashing: The status displays will indicate communication with local and remote I/O modules has ceased.
• OK LED Solid or Flashing Red: On legacy platforms (e.g., 1769-L32E, 1769-L35E), the OK LED will turn flashing red. On 5370 controllers (e.g., 1769-L30ER, 1769-L33ER), it may transition from flashing to solid red depending on the boot progress.
• Studio 5000 / RSLogix 5000 Offline Banner: Connecting to the controller reveals it is in 'No Project' or 'Default' mode.
• Fault Log Code: In Studio 5000 "Controller Properties -> Major Faults," you will see:
  • Type 01 (Power-Up Fault), Code 60: Project loaded from non-volatile memory because the previous project in RAM was corrupt or cleared.
  • Type 01 (Power-Up Fault), Code 61: Project in RAM cleared; no non-volatile memory card image was found to restore.

Possible Causes

1. Depleted Backup Battery (Legacy Controllers): On 1769-L31, L32E, and L35E models, a dead 1769-BA lithium battery fails to sustain the volatile RAM chip when the main 120/240VAC or 24VDC system power is disconnected.
2. Degraded Internal Supercapacitor (Modern Controllers): In 1769-L1, L2, and L3 (5370 Series) controllers, an onboard supercapacitor acts as the energy source to copy RAM contents to internal non-volatile flash storage during a power-down. If this capacitor degrades, the copy operation fails before completion.
3. Inadequate Power Supply Hold-Up Time: If the system power supply (such as a 1769-PA2, 1769-PB2, or 1769-PA4) has failing output capacitors, the DC rail collapses too quickly during shutdown. The PLC does not have the 10-20ms of sustained logic voltage required to save its state.
4. Improper 1769 Bus Termination (End Caps): A loose or missing right-hand bus end cap (1769-ECR) causes signal reflection and electrical noise during the power-down sequence, interrupting the CPU during write operations.
5. Severe Noise / Electromagnetic Interference (EMI): Inductive spikes on the power supply line during system shutdown can garble the controller RAM registers, inducing a checksum error at the next boot.
6. Corrupted SD Card or CompactFlash Card: If configured to load from non-volatile memory on power-up but the storage card contains a corrupt image or is physically degrading.

Step-by-Step Troubleshooting

Follow these sequential diagnostics steps to isolate and resolve the root cause of the power-up fault:

Step 1: Connect and Pull the Fault Log

Do not cycle power again before attempting to connect. Use a USB or Ethernet connection to get online using RSLogix 5000 / Studio 5000. Go to 'Controller Properties', select the 'Major Faults' tab, and note the specific sub-code (Code 60 or Code 61).

• If Code 60 is active, your project restored successfully from an SD/CF card, meaning your RAM was wiped but your backup protected you. Your physical battery/capacitor circuit is still failing.
• If Code 61 is active, your program is completely gone, and you must proceed with hardware checks before downloading the project file again.

Step 2: Test the Memory Backup Hardware

Determine what model of CompactLogix you are running:

• For Legacy Controllers (L32E, L35E, L31): Look at the physical BAT LED on the front bezel. If it is solid red, the 1769-BA battery is depleted. Even without the light, use a multimeter to check the battery terminal voltage. It should read approximately 3.0V DC. Replace any battery that measures below 2.7V DC.
• For 5370 Controllers (L30ER, L33ER, L36ER): These models do not have field-replaceable lithium batteries. They utilize a maintenance-free capacitor. If these units fail to boot after a power cycle of only 5 to 10 minutes, the internal energy storage circuit is broken, and the PLC main board must be replaced.

Step 3: Check System Power Supply Hold-Up Time

Verify the health of the 1769 power module. Using an oscilloscope or a high-speed data logger, measure the decay rate of the 5V and 24V backplane rails when the source breaker is switched off. If the voltage drops to zero in under 10ms, the system power supply capacitors are worn out. Replace the 1769-PA2/PA4 or 1769-PB2/PB4 module immediately.

Step 4: Verify 1769 Bus Termination

Power down the system completely. Inspect the physical right-hand end cap (1769-ECR) and left-hand end cap (1769-ECL, if applicable). Ensure the plastic locking latch is firmly engaged. A loose end-cap causes backplane data corruption when the power drops and the processor tries to terminate active communication loops.

Step 5: Format and Prepare Non-volatile Memory

If a CompactFlash (1784-CF128) or SD Card (1784-SD1 or -SD2) is inserted:

1. Remove the card, place it in a card reader, and check for file corruption.
2. Reformat the card to FAT16 (or FAT32, depending on controller firmware requirements).
3. Reinsert the card into the processor, establish an online connection, and store the updated project to the card configured as "Load on Corrupt Memory."

Recommended Actions

To prevent future occurrences of a Major Fault Type 1, implement the following industrial hardening practices:

• Establish a Preventive Battery Replacement Schedule: For legacy 1769 controllers, change the 1769-BA battery every 12 to 24 months. Always replace batteries while the controller is powered on to prevent the active RAM program from being lost during the exchange.
• Utilize "Load on Corrupt Memory" Configuration: Always install an industrial-grade Allen-Bradley card (e.g., 1784-SD1) and configure the controller properties to load the program automatically from non-volatile flash memory upon corrupt detection. This guarantees that even if a battery or capacitor fails, the PLC loads the valid program and continues running.
• Isolate Source Power via a UPS or Constant Voltage Transformer (CVT): Raw utility mains power can suffer brief sags during plant operations, tripping the PLC's internal shutdown sequence repeatedly. Routing control power through an industrial UPS maintains stable input voltage and prevents incomplete RAM-to-Flash writes.

Recommended Replacement Parts

If hardware degradation is confirmed during your troubleshooting, retrieve these key part numbers for replacement:

• Backup Lithium Battery (Legacy Units): 1769-BA
• Right-Side Bus Terminator End Cap: 1769-ECR
• Left-Side Bus Terminator End Cap: 1769-ECL
• Industrial SD Card (1 GB Capacity): 1784-SD1
• Industrial SD Card (2 GB Capacity): 1784-SD2
• Replacement Power Supply Modules:
  • 120/240V AC Source: 1769-PA2 or 1769-PA4
  • 24V DC Source: 1769-PB2 or 1769-PB4

Related Articles

• How to Configure Non-volatile SD Card Memory on CompactLogix
• Upgrading Legacy 1769-L32E and L35E Controllers to 5370 CompactLogix
• Preventive Maintenance and Battery Replacement Procedures for Allen-Bradley PLCs

FAQ

Q: Why does my 1769-L30ER / L33ER lose its program on a power cycle if it doesn't have a backup battery?

These 5370 series processors use a built-in supercapacitor (not a battery) to power an internal circuit that copies the controller’s volatile RAM memory over to the non-volatile internal flash during a sudden power-down. If you cycle the power off and on too rapidly before this dump process completes, or if the internal capacitor’s capacity has degraded over time, the data cannot be written fully. This results in a Type 1 Code 61 fault on the next boot.

Q: Can I clear a Major Fault Type 1 through RSLogix 5000 and run immediately?

Only if you have configured an image to load from an SD or CompactFlash card. If the RAM was completely cleared and you did not have a valid card inserted, the active system database is empty. You must clear the fault, change your controller mode back to "Program," and download the original, raw *.ACD backup project file from your programming workstation.

Q: What is the real-world lifespan of a 1769-BA lithium battery?

Under active operating conditions where the panel remains powered up, the battery can last up to 5 years since the PLC's internal power supply is sustaining the memory. However, if the control panel is turned off regularly (e.g., during weekend shutdowns, seasonal dry spells, or storage), the battery must do all the heavy lifting. In these scenarios, expect a real-world lifespan of 12 to 18 months.

Q: How do I load an active program onto my SD card so it restores automatically?

Go online with the PLC in Studio 5000. Switch the controller's physical keyswitch to 'REM' or 'PROG'. Open 'Controller Properties' and navigate to the 'Nonvolatile Memory' tab. Select 'Store', select your load parameters (e.g., 'On Corrupt Memory' or 'On Power Up'), and click apply. The PLC will format the project and save an image onto the SD card directly over the backplane bus.