The Red Baron RB‑14/28‑25 is a ramp‑power APU that supplies filtered 14 V or 28 V DC at up to 25 A for aircraft electrical system testing and avionics servicing. Common failure points in this class of units include degraded rectifier diodes, overheating of the internal transformer windings, worn regulator capacitors, and loose or corroded AC input connections that can cause voltage sag or over‑voltage conditions. First‑check diagnostics should verify the AC line voltage and polarity to the APU inlet, confirm the output DC voltage with a multimeter while cycling through 14 V and 28 V modes, and inspect all visible wiring for signs of heat damage or loose terminals before proceeding to internal component testing.[oss-gpt-20b]