Repeatedly removing the MMC card without ESD protection (grounding straps) can zap the card. A corrupted MMC requires a Siemens repair center to re-image, costing >$500.
If you have a physical backup of the program on a .wld or Step7 archive, but the running PLC is password-protected:
Most S7-300 unlock tools (like S7 Unlocker, PLC Guard, or M Key) operate by: unlock s7-300 plc password
If you do not need the existing program—perhaps you have a backup but forgot the write-protection password—you can wipe the CPU.
If you do not need to view the code but just want to wipe the PLC to install a new program, you can perform a factory reset. Repeatedly removing the MMC card without ESD protection
**Warning
Before we dive into the technical details, it is important to address the ethics. PLC passwords exist for a reason: safety and intellectual property protection. Most S7-300 unlock tools (like S7 Unlocker ,
This guide is for educational purposes and for owners attempting to recover access to their own equipment.
If you have physical access to the PLC and the original programming device (PG), you have options. Try these before attempting any third-party hacks.
When you set a password in Step 7, it is not stored as plain text. It is hashed and stored in the system data blocks of the PLC. These tools generally attempt to read the CPU's system data, extract the hash, and either decrypt it or delete it.