Fanuc Alarm 1: TH PARITY ALARM

Fanuc Alarm 1: TH PARITY ALARM

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

Fanuc Alarm 1 (TH Parity Alarm) is a Program / RS-232 Communication alarm that occurs when the CNC control detects an incorrect number of holes (odd/even parity error) while reading a tape or receiving a G-code program via serial communication. Follow this troubleshooting guide to resolve the error.

Official Alarm Description

TH alarm (A character with incorrect parity was input). Correct the tape.

Common Causes

This alarm is triggered during program transfer or MDI entry due to the following reasons:

• Corrupted G-Code File: The program being transmitted contains illegal characters or corrupted data bytes.
• RS-232 Cable Fault: Loose, damaged, or poorly shielded serial cable causing noise during data transmission.
• Baud Rate / Parity Mismatch: Communication parameters (Baud Rate, Stop Bits, Parity) on the CNC controller do not match the DNC software settings.
• Faulty Paper Tape Reader: Dirt, dust, or worn-out optical sensors inside the paper tape reader (on older CNC machines).

Step-by-Step Troubleshooting & Solution

Follow these practical steps to fix Fanuc Alarm 1 and restore communication:

1. Check the Program File: Open the G-code file on your PC/DNC software using a text editor (like Notepad). Ensure there are no strange symbols, unwanted control characters, or line noise.
2. Verify Communication Parameters: Ensure the RS-232 settings match on both the PC and CNC machine:
   • Parity: Even (E) or None (depending on system configuration)
   • Stop Bits: 2
   • Data Bits: 7 or 8
3. Inspect the RS-232 Cable: Check the serial cable connectors for loose pins or bad soldering. Ensure the cable is shielded and kept away from high-voltage power lines to prevent electromagnetic interference.
4. Clean Tape Reader (If Applicable): If reading from paper tape, clean the optical reader head with isopropyl alcohol to remove dust.
5. Clear the Alarm: Press the RESET button on the MDI panel to clear the error notification once the file or cable issue is resolved.

Frequently Asked Questions (FAQs)

Q1: Does Fanuc Alarm 1 indicate a hardware failure on the CNC board?

No, this is almost always a data transfer error caused by cable noise, bad serial parameters, or a corrupted G-code file.

Q2: How do I clear Alarm 1 after fixing the cable/file?

Simply press the RESET key on the CNC operator panel. If the error reoccurs during the next file transfer, re-check your DNC communication settings.

Have you faced Fanuc Alarm 1 TH PARITY ALARM on your machine? Share your experience or troubleshooting tips in the comments below to help other CNC operators and programmers clear this error faster!