Panasonic FP7 — ALARM/ERROR LED Self-Diagnostic

Panasonic · beginner · 20 min

A Panasonic FP7 ALARM/ERROR LED has a self-diagnostic code you read in FPWIN GR7. A power-cycle-in-PROG test separates a real unit fault from noise, and an ALARM after RUN usually means scan time is too long.

ℹ️ The FP7 distinguishes alarm/error (unit stops) from warning (unit keeps running). Read the self-diagnostic code in FPWIN GR7 rather than guessing from the LED.

Alarm/error vs. warning

On a Panasonic FP7 (and FP0H) PLC, the ALARM / ERROR LED signals a self-diagnostic condition. The behavior tells you the severity: when an alarm or error occurs, the unit stops operation; when a warning occurs, the unit continues operating. So an ALARM LED with the PLC stopped is more serious than a warning indication.

Read the self-diagnostic code in FPWIN GR7

1. In FPWIN GR7, go to Monitor → Status Display.
2. Read the PLC Error Flag field — it shows the self-diagnostic error.
3. To clear a self-diagnostic error, switch the CPU to PROG. mode (many self-diagnostic errors clear on the mode change once the cause is gone).

For a syntax error, use Debug → Totally Check Project in FPWIN GR7 to locate the exact offending instruction in the program.

The power-cycle-in-PROG test (real fault vs. noise)

For an ALARM LED on FP7, this quick test tells you whether it's hardware or transient:

1. Switch the CPU to PROG. mode, then turn the power supply OFF and back ON.
2. If the ALARM LED lights again, there may be a problem with the unit (hardware) — investigate/replace.
3. If the ALARM LED goes out after the off/on, the fault was likely caused by noise or another temporary phenomenon — improve grounding/noise immunity and monitor.

Scan-time cause (ALARM after RUN)

1. Switch to RUN mode. If the ALARM LED turns on after switching to RUN, the program is taking excessive time (scan-time / watchdog related).
2. Review and modify the program to reduce scan time — long loops, heavy instructions, or blocking operations are typical causes.

Step-by-step

1. Read the code: FPWIN GR7 → Monitor → Status Display → PLC Error Flag.
2. Syntax error: run Debug → Totally Check Project to find it.
3. ALARM test: in PROG mode, power OFF/ON — re-lights = unit fault; clears = noise/temporary.
4. ALARM after RUN: the scan is too long — optimize the program.
5. Clear by switching to PROG mode once the cause is resolved.

Verify

After the fix, confirm the ALARM/ERROR LED is off and the PLC Error Flag is clear in FPWIN GR7. If ALARM returns on RUN, the program scan is still too long; if it returns on power-up in PROG, treat it as a unit hardware fault.