The Thorn Automated Systems RPS‑424 (part #910683) is a solid‑state power supply that delivers filtered, regulated DC to the AUTOCALL TFX fire‑alarm system and often includes an optional Power Supply Monitor (PSM). Common failure modes for this unit are input voltage dropout or overload causing the internal regulator to shut down, capacitor degradation leading to ripple or output noise, fuse blowouts, and shorted output rails due to component burn‑out. First‑check diagnostics should include verifying the AC input voltage and line frequency, measuring the DC output with a multimeter while monitoring for correct voltage levels, inspecting the board for burnt components or swollen electrolytics, and reviewing any error codes displayed on the connected fire‑alarm panel.[oss-gpt-20b]