If the input voltage exceeds the optocoupler's rated voltage, the internal LED might burn out, causing a malfunction. How to Fix It: Double-check the voltage levels on the input and output sides of the optocoupler. Incorrect circuit wiring: The connections to. Optocouplers like the 6N137SDM are susceptible to several types of faults, including: Failure of the LED: The LED inside the optocoupler may degrade or burn out due to overcurrent, high temperatures, or electrical surges. In this article, we will break down the causes of this burnout and offer step-by-step solutions to avoid or fix this issue. However, like any other electronic component, it can experience issues over time due to various reasons.