Sevcon Millipak 633T45320 is a 24‑/48‑V, 500 A separately‑excited DC motor controller designed for industrial traction and heavy‑duty drives. Common failure modes include power supply over‑voltage or undervoltage causing the internal regulator to trip, field winding insulation breakdown leading to loss of torque control, overheating of the IGBT module under sustained high current, and firmware corruption that can lock the unit in a fault state. First‑check diagnostics: verify input voltage stability and continuity on the 24/48 V rails; inspect the IGBT heat sink and case for excessive temperature or thermal paste degradation; review the controller’s diagnostic LEDs or serial log for error codes related to overcurrent, overtemperature, or field‑winding faults.[oss-gpt-20b]