Use an oscilloscope or multimeter to see if Pin 6 (Output) toggles when the input trigger is activated. If the input changes but the output stays dead, the IC is likely fried. Conclusion
Understanding the YL105 IC: A Comprehensive Guide and Datasheet Overview yl105 datasheet
These chips are sensitive to voltage spikes. Ensure the regulated DC voltage reaching the chip is stable. Use an oscilloscope or multimeter to see if
Sets the operational logic (High/Low trigger). yl105 datasheet
Sends the signal to the load-switching component (Relay/Triac).
Extremely low (micro-ampere range in standby), making it ideal for energy-efficient "green" appliances.