The working condition of the filament power control circuit in CINRAD/SA Radar in is described in detail and the characteristics of the pulse width modulator control circuit SG1525A are analyzed. The debugging is conducted on the key waveforms which control the chopper pulse width modulation circuit and the oscillator control circuit, as well as the filament power supply output voltage and filament voltage and current protection step by step. The procedures and techniques of filament power fault diagnosis and troubleshooting are summed up based on actual experiences, to provide a reference for the troubleshooting of radar filament power supply failure.