MITSUBISHI A-series PLC Troubleshooting Replacement

Transient power failure occurred during scanning, resulting in a false increase in scanning time.

solve:

Check if there is an infinite loop or excessively long sequence in the program, and use the CJ instruction to jump to unrelated segments.

Monitor special register D9005. If it is not 0, it indicates power fluctuation and the power supply line needs to be checked.

The watchdog setting value can be appropriately extended (through parameter settings).

5. Fuse Break OFF (error code 32)

Phenomenon: The CPU continues to run (RUN state), but the ERR LED of the corresponding output module lights up.

Reason: The internal fuse of the output module is blown (usually due to a short circuit of the output load).

solve:

Observe the fuse indicator LED on the output module panel and replace it with a fuse of the same specification.

Read the special registers D9100~D9107 through peripheral devices to identify which module (bit 1) is specific.

6. Unit verification error (UNIT VERITY ERR., error code 31)

Phenomenon: CPU stops.

Reason: The configuration of the I/O module after power on is inconsistent with the actual module currently inserted (for example, someone unplugged and plugged in the module).

Solution: Check the special registers D9116~D9123, and the module corresponding to bit 1 has changed. Re plug or replace it.

7. Battery Error (BATTERY ERROR, error code 70)

Phenomenon: The ERROR LED flashes while the CPU is running, or an alarm is triggered when powered on.

Reason: Low battery voltage or disconnected battery.

Solution: Immediately replace the battery (model A6BAT). Before replacement, ensure that the PLC is powered on (or connected to an external power source through the programming port) to prevent program loss. Reset the "low battery" flag in the parameters after replacement.

8. Special module layout error (SP. UNIT LAY. ERR., error code 44)

Phenomenon: CPU stops.

Possible reasons:

Installed 3 or more computer link modules (up to a maximum of 2).

Installed 2 or more MELSECNET modules.

The I/O allocation in the parameters does not match the actual module type (such as setting a special module as a regular I/O).

Solution: Reduce the number of modules or correct parameter allocation.

Maintenance and battery replacement

1. Daily inspection items (recommended for each shift)

Power LED, RUN LED, ERROR LED status.

The input/output LED is consistent with the actual device status.

No abnormal noise or odor.

2. Regular inspections (every 6-12 months)

Environmental temperature and humidity (0-55 ℃, 10-90% RH).

Check if the wiring terminals are loose (torque check).

Internal dust accumulation (cleaned with a vacuum cleaner).

Battery voltage status: Monitor special relays M9006 (low battery voltage warning) and M9007 (low battery voltage error). If M9006 is ON, replacement should be arranged.

3. Battery replacement steps

Ensure that the PLC power is turned on (at least 1 minute).

Open the front panel of the CPU and unplug the old battery connector.

Insert a new battery (A6BAT), pay attention to polarity.

Close the panel. After replacement, M9006/M9007 should be reset.

If it needs to be replaced in a power-off state, it must be completed within 5 minutes, otherwise the program will be lost (backup is required in advance).