Coil internal short circuit test circuit

When a local short circuit occurs in the motor stator coil, it cannot be measured with a multimeter. The test circuit as shown in the figure can complete the internal short circuit test of the coil. Transistor VT, inductor coil L and capacitors C1, C2, etc. form a capacitive three-point oscillation circuit. When the measured sub-coil is connected across the A and B ends of the oscillation circuit, if there is no short-circuit fault, the measured coil shows high impedance, which does not affect the operation of the oscillator, and the mA pointer of the milliamp meter has no obvious movement. When the coil under test has a short-circuit fault, connecting it in parallel to ends A and B will cause the Q value of the oscillation circuit to drop, causing the oscillation to weaken or stop. At this time, the reading of the mA meter will drop rapidly.