Synco MC4 Benutzerhandbuch Seite 11

23. USB power supply interface
Can be connected to an external 5V power supply or computer USB interface. When
connected with computer, the console functions with external sound card.
24. MP3/PC connection working status switch
When the console is powered by computer, you can switch the connection between
MP3 and PC by this button; when the console is powered by an external 5V power
supply, it can only switch to the corresponding status of MP3.
11