Epson DFX-9000 - Manual (Page 106)

106 Control Panel
2. Turn on the printer while holding down both the Font and
Pitch buttons. The printer beeps twice, indicating that the
lock-out mode has been turned on.
To turn off the lock-out mode, repeat steps 1 and 2. The printer
beeps once, indicating that the lock-out mode has been turned off.
See “Changing the settings in the default-setting mode” on page
103 for instructions on how to change the functions to be locked.