Work through illustrated diagnostic scenarios that separate network, configuration and device problems. This practical casebook covers missing stations, device names and addresses, replacement hardware and connection faults using a TIA Portal / STEP 7 V21 baseline. Each case presents a symptom, evidence checkpoints, a worksheet and explained findings. Build a repeatable method for establishing fault scope, verifying the physical path, checking device identity and interpreting module diagnostics. An independent educational resource for maintenance technicians; not affiliated with Siemens AG or PROFIBUS & PROFINET International.