The difference in appearance between positive and negative high-frequency variable resistance diodes and ordinary diodes is their color code. The color code of ordinary diodes is generally black, while the color code of high-frequency variable resistance diodes is light. Its polarity pattern is similar to that of ordinary diodes, where the end with a green ring is the negative electrode and the end without a green ring is the positive electrode. How to adjust the red and black probes of the multimeter to measure the resistance between the two pins of the varactor diode? The resistance value between the two pins of the varactor diode should be infinite. If during the measurement, it is found that the pointer of the multimeter swings slightly to the right or the resistance value is zero, it indicates that the measured varactor diode has a leakage fault or has already broken down. A monochromatic LED is attached to an energy-saving 1.5V dry battery outside the multimeter, and the multimeter is set to R × 10 or R × 100 gears. This connection method is equivalent to applying a 1.5V voltage in series to the multimeter, increasing the detection voltage to 3V (the opening voltage of the LED is 2V). During testing, rotate the two probes of a multimeter to contact the two pins of the LED. If the performance of the tube is good, it must be able to emit light normally once. At this time, the black lead is connected to the positive electrode and the red lead is connected to the negative electrode
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