The winding of an electronic transformer has a shielding winding. Is there a test method to detect the leakage of shielding winding in finished products? How to detect the transformer when it is not installed on PCB? The shielding winding should have a fixed grounding lead, which can be judged by measuring the parasitic capacitance of this pin and the adjacent winding. The parasitic capacitance values of shielding winding and adjacent winding (which need to be fixed) can be measured by the capacitance file of digital multimeter (transformers of the same type should be basically the same). If it leaks, this value should be zero. You can also use this parasitic capacitor to build an oscillator and make a special detection tool, such as ringing the bell when there is a capacitor, so that you can judge quickly.