Fanuc Alarm 75: PROTECT

Fanuc Alarm 75: PROTECT

Fanuc Control Model: Fanuc 0i, 16i / 18i / 21i, 30i / 31i / 32i

Fanuc Alarm 75 (PROTECT) is a memory/program protection alarm that occurs when an operator attempts to edit, insert, or delete a program block or parameter while the Program Protect Key is switched ON or memory write protection is enabled.

Official Alarm Description

An attempt was made to register a program whose number was protected.

Common Causes

• Program Protect Switch Turned ON: The physical key switch on the machine control panel is locked (protect mode active).
• PMC Signal Active: The memory protect signal (KEY signal like KEY1, KEY2, KEY3, or KEY4) is sent from the PMC.
• 8000/9000 Series Program Protection: Attempting to edit a macro program or locked subprogram protected by parameters (e.g., Parameter 3202).
• MDI Mode Lock: Attempting to alter data in EDIT mode when the machine mode selector is set incorrectly or write-protected.

Step-by-Step Troubleshooting & Solution

1. Turn OFF the Memory Protect Key:
   • Locate the physical Program Protect Key switch on the CNC operator panel.
   • Turn the key to the OFF / UNLOCK position (usually marked with an open lock icon).
2. Verify Correct Machine Mode:
   • Ensure the mode selector switch is set to EDIT mode (for editing programs) or MDI mode (for entering MDI commands).
3. Check Protected Program Parameters (8000/9000 Macros):
   • If you are editing an O8000–O8999 or O9000–O9999 program, press SYSTEM $\rightarrow$ PARAMETER.
   • Check Parameter 3202 (NE8 / NE9 bits):
     • Set NE8 = 0 to enable editing of 8000-series programs.
     • Set NE9 = 0 to enable editing of 9000-series programs.
4. Verify PMC Key Signals (Advanced Check):
   • If the physical key switch is OFF but the alarm persists, check the PMC diagnostic status for signals KEY1 through KEY4 to ensure the key switch wiring or relay is not faulty.
5. Clear the Alarm:
   • Once protection is turned off, press the RESET button on the MDI panel to clear the alarm display and resume editing.

G-Code / Program Editing Example

Pressing [INSERT] or [ALTER] while Program Protect Key is ON $\rightarrow$ Triggers Fanuc Alarm 75 (PROTECT).

Turn Protect Key OFF $\rightarrow$ Switch to EDIT mode $\rightarrow$ Press [INSERT] or [ALTER] $\rightarrow$ Editing succeeds.

Frequently Asked Questions (FAQs)

Q1: Can I run a program if Alarm 75 is displayed?

Yes, Alarm 75 only blocks program registration and editing. It does not stop an already loaded program from running in AUTO/MEM mode.

Q2: What should I do if the machine does not have a physical protect key?

On some modern compact Fanuc panels, protection is controlled via a software setting under the SETTING (HANDY) screen (Parameter Write Enable / Program Protect toggle) or via PMC signals.

Have you faced Fanuc Alarm 75 PROTECT on your machine? Share your experience or troubleshooting tips in the comments below to help other CNC operators and programmers clear this error faster!