The Sab Nife Corp SMR 48/50 4724‑68‑40201‑01 is a high‑current AC‑to‑DC rectifier/power supply designed for legacy telephone line backup systems, typically delivering 48 V or 50 V DC to maintain rotary phone service during outages. Common failure modes in this class include degraded bridge diodes, failing filter capacitors, and overheating of the internal transformer windings due to prolonged duty cycles; symptoms often show as intermittent power loss, elevated output voltage ripple, or excessive heat at the chassis. Begin troubleshooting by verifying that the input mains is within spec and that the unit’s output voltage matches its rating under load; inspect the rectifier bridge for visual signs of arcing or burn marks, test electrolytic capacitors with a capacitance meter, and check the transformer windings for continuity and insulation resistance. If these checks are normal, review any error logs from connected telecom equipment to rule out external faults.[oss-gpt-20b]