Fangrui Product Details Features: 1. Test To Confirm That The Board Under Test Is Turned Off And The Electrolytic Capacitors On The Motherboard Are Fully Discharged. It Is Strictly Forbidden To Test When The Motherboard Is Powered On. 2. Confirm The Optocoupler Pin1 (the Pin With A Small Dot On The Test Board Also Has A Corresponding Mark 1 Pin) 3. Connect The Optocoupler Test Board To The Usb Power Cord, And Test The Optocoupler With The Test Board Probe Contact Point. If The Light In The Optocoupler Test Board Keeps Flashing, It Means That The Optocoupler Is Good (the Light Brightness May Be Different From The Optocoupler). As Long As It Flashes, It Means That The Optocoupler Is Good) 4. Measure To Ensure That The Optocoupler Test Board Has Good Contact With The Tested Optocoupler If The Indicator Light Is On Or Off, Remove The Optocoupler From The Circuit Board And Insert It Into The Optocoupler Seat Of The Breadboard To Reconfirm The Test Results Applicable To 4-pin Optocouplers, Other Types Of Optocouplers Are Temp