Thanks for the tip, I will check the board once more.
Can the resistor be the source of the problem? It seems that this 680 ohm resistor is being used to protect the LED. I wanted to know whether it works fine. Therefore, I checked the Eagle files (V3.0 - 328) but I could not find this resistor on it. The announced Eagle schematic on the webpage has some inconsistencies (330 ohms instead of 680 ohms). Where to find the corresponding resistor?
Regards