: If the board "boots loops" or shows a flashing standby LED, it often requires a firmware re-flash via the USB port or an SPI programmer like the CH341A .
Pin 3 (FB) is the most sensitive. The schematic will show a resistor divider network or a direct connection to a PC817 optocoupler. If the feedback loop is broken, the output voltage will skyrocket. T.sk105a.03 Schematic Diagram