1, test to confirm that the board under test has been powered off, and the electrolytic capacitors of the motherboard days have been fully discharged. It is strictly prohibited to test when the motherboard is energized. 2, confirm the optocoupler pin 1 (with a small dot on the foot test board also has the corresponding 1 feet of the logo) 3, the optocoupler test board connected to the USB power cord, the test board probe contact need to test the optocoupler, if the optocoupler test board on the light has been blinking, said the optocoupler is good (the brightness of the light may not be the same as long as it is blinking means that the optocoupler is good) 4,Measurement to ensure that the optocoupler test board and the measured optocoupler have good contact 5, if the indicator light is often bright or not bright, the photocoupler can be removed from the circuit board and inserted into the photocoupler seat of the test board to reconfirm the test results. applies to 4-pin optocoupler, other types of optocoupler is not suitable for the time being Note: This product is only for professional electronic maintenance personnel. People who do not have professional electronic knowledge should not buy and use it! Please bring your own Type-C power cord. The color of the needle mounting base on the tester is random due to different batches, and the specified color is not accepted; the actual product may have color difference due to different lighting or display Colour:Green/Blue Material:PCB+electronic components<br><br>Package Contents: 1 x Optocoupler Tester Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.