Fenwal Inc 74‑100009‑01 is an industrial AC‑to‑DC power supply module used in Fenwal fire‑alarm and protection system panels, providing up to 4 A of regulated 24 VDC output through a switching regulator. Common failure modes for this class include degraded electrolytic capacitors on the input or output rails, over‑temperature MOSFETs or driver ICs, and transformer winding insulation breakdown; these often present as brown‑out power, overheating, or erratic voltage regulation. First‑check diagnostics should verify that the unit receives proper 115/230 VAC input (voltage, phase, polarity), measure the output rail for correct voltage and ripple, inspect the PCB for burn marks, bulging capacitors, or loose connections, and review any error codes displayed on the host panel.[oss-gpt-20b]