Determine the polarity of the diode. Pinch one end of the diode directly with your hand, touch the other hand to the touch electrode of the test pen, and use the probe to touch the other end of the diode. If the light-emitting diode inside the test pen glows, it means that the pinched end is the positive electrode of the diode, and the end that is in contact with the probe of the test pen is the negative electrode; if the light-emitting diode does not light up, the situation is just the opposite. Here, the hand holding one end of the diode is equivalent to the black test pen when judging the polarity of the diode with the ohm block of the pointer multimeter, and the detection pole of the electric test pen is equivalent to the red test pen. After mastering this rule, you can also use a test pen to determine whether the resistor is open, and the polarity of transistors, thyristors, etc. The specific method readers can use their brains and hands to summarize, and I will not repeat them here. It is more convenient to operate than a multimeter because both hands are used instead of test pens that are commonly used for measurement.
