Hello,
i work usually with Chinese Arduino ( uno ) . But it's always complicated to works with CH340 on OSX.
I bought a official Arduino Mega R3.
i have led ON in green and blink on L "led" in "orange"
But i have not usb detection on OSX and also on windows laptop. ( nothing in device manager - no unknow device ).
I burn the bootloader since one uno. The transfert is ok but no change.
Thank you to help me.