IDEC FC6A Fault Diagnostics and Troubleshooting in WindLDR
Key Takeaway
How to diagnose and resolve faults on IDEC FC6A PLCs — LED status codes, error registers, watchdog faults, I/O diagnostics, and building fault annunciators.
Quick Answer
The IDEC FC6A provides diagnostic information through front-panel LEDs, special relay (SP) error flags, and the WindLDR System Monitor. Most faults can be diagnosed by checking LED states, reading error code registers, and examining SP relay bits in the program.
Status LED Overview
- PWR (green) — Power supply status. Solid = normal.
- RUN (green) — Solid = program executing. Off = STOP mode.
- ERR (red) — Flashing = non-fatal error. Solid = fatal CPU error halting execution.
- COM (green) — Communication activity indicator.
- BAT (red) — Battery low for retentive memory and RTC backup.
Reading Error Codes in WindLDR
Connect online and open System Monitor → Error Log to view timestamped error entries with error type and code. Common error types include CPU errors, I/O expansion bus errors, communication timeouts, and program errors.
Common Error Types
- CPU error — Internal processor fault. May require firmware reload or hardware replacement.
- I/O error — Expansion module not recognized or communication lost. Check module seating and bus cable.
- Communication error — Serial or Ethernet timeout. Verify wiring, settings, and remote device status.
- Battery low — Replace the backup battery to preserve retentive memory and RTC on power loss.
Special Relay Error Flags
SP relays SP50 and above flag specific system conditions in real time. Use these bits in ladder logic to trigger alarms, activate warning outputs, or log fault events:
- SP50 — CPU error flag
- SP51 — I/O bus error flag
- SP52 — Communication error flag
- SP53 — Battery low flag
Watchdog Timer Fault
If the program scan exceeds the watchdog timeout, the FC6A halts execution and sets the ERR LED. Common causes: excessive loop iterations, blocking communication calls, or overly complex single-scan routines. Remedies: optimize the program, increase the watchdog timeout, or distribute processing across multiple scan cycles.
Building a Fault Annunciator
Use SP error flags in ladder logic to set M relays and store error codes in R registers with timestamps. Display fault status on an HMI screen and log events to the SD card for post-incident analysis.
Factory Reset
Perform a factory reset via WindLDR System Settings while online, or by holding the reset button during power-up (procedure varies by hardware revision). Factory reset clears the program and all retentive memory.
Frequently Asked Questions
A flashing ERR LED indicates a non-fatal error (communication fault or warning). A solid ERR LED indicates a fatal CPU error that halted program execution.
Factory reset is performed through WindLDR System Settings while online, or by holding the reset button during power-up.
Special relay bits (SP50+) flag system conditions including I/O errors, communication faults, and battery low. Use these in ladder logic to trigger alarms and log events.