1. Ensure the board under test is powered off and all electrolytic capacitors on the motherboard are fully discharged. Testing while the motherboard is energized is strictly prohibited. 2. Verify the optocoupler pin 1 (marked with a small dot on the component; the test board also has a corresponding “1” label). 3. Connect the optocoupler test board to a USB power source. Touch the test probes to the optocoupler pins. If the indicator LED blinks, the optocoupler is functional (blinking indicates functionality regardless of brightness). 4. Ensure firm and stable contact between the test board and the optocoupler during measurement. 5. If the indicator LED remains constantly lit or does not light up at all, remove the optocoupler from the circuit board and insert it into the dedicated socket on the test board to retest. Compatible with standard 4-pin optocouplers only. Not suitable for other optocoupler types at this time. Note: This product is intended for professional electronics technicians only. Individuals without formal electronics training should not purchase or operate this device. A USB Type-C power cable is required but not included. The color of the probe holder may vary by batch; specific color requests cannot be accommodated. Slight color variation may occur due to lighting or display differences. Color: Green / Blue Material: PCB + electronic components Package Includes: 1 x Optocoupler Tester (No additional accessories included.) Note: Screen/display settings and lighting conditions may cause minor color discrepancies between images and the actual product. Measurement tolerance: ±1–3 cm.