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Recovering a Locked-Out Control System — Textile Yarn-Warping Machine

Siemens Reverse Engineering Controls Migration Textile

A yarn-warping machine's Siemens S7-200 PLC was password-locked with no recoverable credentials — the plant had no way to maintain or modify it. I reverse-engineered the machine's control logic from its physical behavior and re-implemented it from scratch on a Siemens S7-1200 with a TP700 panel, reusing the existing drives and motors to keep the project on budget.

Scope of Work

  • Reprogrammed the machine's control logic entirely from scratch — the original PLC program was inaccessible.
  • Migrated from Siemens S7-200 to S7-1200 with a TP700 HMI panel.
  • Reused the existing Fuji servo drive, Meiden AC drive, and motors to control project cost.
  • Improved fault and alarm capture versus the original, undocumented system.

Architecture

The new S7-1200 controls the winding drum, thread-tensioning brake, horizontal drum traverse, and fold-plate hydraulics, all connected to the TP700 HMI over Ethernet.

Technology

  • Siemens S7-1200, TP700 HMI
  • Fuji Electric servo drive, Meiden AC drive (reused)
  • EtherNet
New Meiden AC drive and control panel Siemens S7-1200 PLC rack and Faldic servo drive