Fujitsu FI‑5120C is a high‑speed duplex color document scanner designed for office and industrial use, featuring an automatic document feeder (ADF) capable of 34‑inch documents and ultrasonic double‑feed detection. Common failure modes include ADF jam or misalignment, optical sensor faults leading to image distortion, motor drive issues causing scanning speed loss, and firmware corruption that can trigger error codes such as “E100” or “E200”. First‑check diagnostics: verify the power supply voltage and ensure the unit is receiving clean 120 V/240 V; inspect the ADF for paper jams or debris and confirm the rollers are lubricated and not worn; review the scanner’s diagnostic screen or USB log for error codes, then test a simple scan to isolate mechanical versus firmware problems.[oss-gpt-20b]