Demonstrating PLC decryption with Mitsubishi FX3U PLC as an example

If you're involved in automation and industrial control, have you ever faced any of these issues? It's quite common in the field. Let's take a look at some of the typical problems engineers encounter.

1. The PLC on your machine is damaged, and you need to replace it with a new one. However, the existing program is password-protected, making it impossible to retrieve.

2. You're trying to perform maintenance or upgrade on equipment, but the PLC is encrypted, and there's no access to the original program, making modifications difficult.

3. You want to understand how the equipment works, study its process, and learn the PLC program to improve your skills and knowledge.

4. The manufacturer has densely packed the PLC, and they’re not providing technical support for various reasons, leaving you stuck.

5. The touch screen needs parameter adjustments during use, or it's broken and can't be used. The program can't be uploaded due to restrictions, making troubleshooting a challenge.

If you've experienced any of these issues, this article might help you find a solution. But before we go further, let’s clarify one thing: while some may see this as a "hack," we must emphasize that the purpose here is not to violate intellectual property rights. Instead, it's about gaining access to critical systems when necessary for maintenance, learning, or improvement.

Many times, old equipment breaks down, and the original manufacturer may no longer be available. In such cases, having the right tools can make all the difference. Today, we’ll walk through a real-world example using a Mitsubishi FX3U PLC to demonstrate the decryption process step by step.

Step 1:

Turn off the PLC power. Open the cover located directly above the unit. Inside, you'll find a rectangular port. Count from the left, and locate the ninth pin. Use thin tweezers or wires to short the upper and lower pins at position nine.

Step 2:

Power the PLC back on. The alarm light will flash. At this point, remove the shorted wire or tweezers. Don’t turn off the power. Open the decryption software, select the communication port, and click "Decrypt" to read the first password. Write it down and close the software.

Step 3:

Connect the PLC to your computer using a data cable. Open the dedicated decryption tool, read the password (only one), note it down carefully, and then close the software.

Step 4:

Open the programming software and try to communicate with the PLC. When prompted for a password, enter the first one. The second password is usually not required. Click OK to read the program.

Step 5:

Use the programming software to log in and modify the two passwords. After changing them, power off and restart the PLC for the changes to take effect.

Note 1:

If you don’t change the password while the PLC is in alarm mode, it will retain the original password after being powered off. This means the second password remains unknown, and the program still cannot be uploaded.

Note 2:

The program retrieved in alarm mode is often incomplete. To get the full program, you must first reset both passwords and restart the PLC. This is a crucial step.

Tip 1:

The FX3U example is just one of many possible methods. Different PLC models and brands require different approaches, but understanding the underlying principles is key. Practice and patience are essential.

As the saying goes, “There’s no skill in the road, but it’s tangible in the middle.” Some details may not be fully explained here, so experimenting and thinking critically will help you grow in your career.

Tip 2:

Once again, technology should serve progress and innovation. Using these techniques for unethical or illegal purposes is completely different from the intent of this article. We encourage all automation professionals to act with integrity and respect for intellectual property.

Tip 3:

Finally, here’s a small collection of PLC decryption tools (note: these are from the internet, and users should verify their safety and legality). If used properly, these tools can significantly enhance your work efficiency and problem-solving capabilities.