As shown, the detector consists of a buck rectifier circuit, an oscillator and a missing pulse detector, and an LED indicating circuit.
VT1, VT2, RP1, R1, R6, C2, C3, etc. constitute an emitter-coupled venturi bridge, and the oscillation frequency is about f1=5KHz. When the output transformer to be tested is connected to the C1 input, the oscillator becomes a three-point capacitor. Due to the intervention of the inductors L and C1, the oscillation frequency becomes 10 kHz to 30 kHz.
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