User`s manual

Troubleshooting Troubleshooting
11 – 18
11.2.18 When program is rewritten unintentionally
When a program is unintentionally rewritten at power-on or reset of the programmable controller,
check special relay SM660.
● When SM660 is OFF ("Program memory execution"): A hardware fault may have occurred.
Please consult your local Mitsubishi service center or representative, explaining a detailed
description of the problem.
● When SM660 is ON ("During boot operation"): After formatting the program memory that is
performing boot operation from the standard ROM, write data to the standard ROM.
Invalidate the "Perform boot from standard ROM" check box in the boot file setting of the
PLC parameter dialog box. Write the parameters and sequence program to the program
memory.
Power on the programmable controller/perform reset operation.
If the program is rewritten a hardware fault may have occurred. Please consult your local
Mitsubishi service center or representative, explaining a detailed description of the problem.
If the program is not rewritten, troubleshooting is completed.