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What to Do If You Forget the PLC Password:

If you forget the PLC password, you must clear the PLC memory and reload your program. Clearing the PLC memory puts the PLC in STOP mode and resets the PLC to the factory-set defaults, except for the PLC address, baud rate, and the time-of-day clock.
To clear your program in the PLC, select the PLC > Clear?menu command to display the Clear dialog box. Click on all of the checkboxes and confirm your action by clicking the OK button. This displays a password authorization dialog box. Entering the Clear password, clearplc, allows you to continue the Clear All operation.

The Clear All operation does not remove the program from a memory cartridge. Since the memory cartridge stores the password along with the program, you must also reprogram the memory cartridge to remove the lost password.