ZAPI Inc SEM‑2 is a high‑frequency chopper controller designed for separately excited DC motors up to 5.5 kW, featuring MOSFET switching, microprocessor logic and digital console programming. Common failure points in this class include burnt MOSFETs or gate drivers, degraded capacitors on the power stage, and overheating of the heat sink due to insufficient airflow or thermal paste loss. First‑check diagnostics: verify input AC voltage and polarity, inspect for visible burn marks or swollen electrolytics on the DC side; confirm that the digital console reports no fault codes and that the motor windings are intact. If power is present but output torque is absent, test MOSFET gate drive signals and measure the chopper ripple current to isolate a faulty switching element.[oss-gpt-20b]