Applicable Systems
FBs-MA
FBs-MC
FBs-MN
B1
HB1
Symptoms
When attempting to run the PLC, a ladder logic checksum mismatch is detected. The PLC cannot enter RUN mode and returns error code 5 to indicate that the ladder program integrity check has failed.
Possible Causes
- Ladder program corruption due to power interruption during program write
- Memory module degradation or hardware fault
- Mismatch between the program stored in flash and the working copy in RAM
Troubleshooting Steps
- Step 1: Connect to the PLC using WinProladder software and attempt to read the ladder program
Software can communicate with the PLC and display the program contents - Step 2: If the program reads correctly, recompile and download it to the PLC to refresh the checksum
Download completes successfully and checksum is recalculated - Step 3: If the program cannot be read, restore from a known-good backup file
Backup program downloads successfully and PLC enters RUN mode - Step 4: If the problem persists after restoring the program, replace the CPU module or memory cartridge
New hardware accepts the program and passes checksum verification
How to Reset
To reset: 1) Re-download the ladder program using WinProladder. 2) Cycle power to the PLC. 3) Attempt to enter RUN mode. If the error persists, replace the memory module.
Common Replacement Parts
- FBs-CM55E: Memory cartridge for FBs series PLC (Verify compatibility with the specific CPU model before replacement)
Frequently Asked Questions
- Q: What causes a ladder checksum error on FATEK PLC?
Typically caused by program corruption from power loss during write operations, or memory hardware degradation. Re-downloading the program usually resolves it.
- Q: Can I recover the program from a PLC with a checksum error?
If WinProladder can still communicate with the PLC, you may be able to upload the program. If not, you must restore from a backup file.
Source: FATEK FBs Communication Protocol Manual, Appendix 1
Category: PLC & VFD