The most common method is the multimeter test. When using a multimeter to detect LEDs, you must use the “R×l0k” file. The tube voltage drop of the LED is about 3V, and the multimeter is in the "R × lk" and below.
The battery inside the watch is only 1.5V. Below the tube pressure drop. Regardless of the forward and reverse access, the LED is unlikely to be turned on and cannot be detected. The "R × 1k" file is connected to a 9V (or 15V) high-voltage battery, which is higher than the tube voltage drop, so it can be used to detect LEDs.
During the detection, the two test leads are respectively connected with the two leads of the light-emitting diode, such as the deflection of the hands half, and there is a bright spot in the light-emitting diode, indicating that the light-emitting diode is forward-connected, and the black test pen (with the battery in the table) The positive electrode is connected to the positive electrode; the negative electrode is connected to the red test pen (connected to the negative electrode of the battery in the watch).
Then adjust the two test leads and connect them with the LEDs. In this case, the reverse direction is applied and the hands should not move. If the hands are deflected to the head or not moving, either forward or reverse, the LED is damaged.
We can easily see the two block-shaped pins inside the LED. We call it the led bracket. The negative pole bracket is relatively large. The reason is that the negative bracket supports the led chip, and the positive bracket is relatively small!
So we came to the conclusion: "Visual inspection, inside the led, the pin of the large connection of the bracket is the negative pole, the pin of the small link of the bracket is the positive pole", and a relatively simple method is, if your LED night light is If the pin is still sound, if you look at the length of the pin directly, you can separate the "positive pin is longer".
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