Pioneer DDJ SB2 - Deck 2 has no Sound

Hello, 

my Pioneer DDJ SB2 works only with one deck. If i load a track to the second deck and hit play, there is no sound output. The LED indicators from the controller dont show any signal, but on deck 1 they do.
I think i have to set only one option to "activate" the second channel.

I use serato DJ Intro 1.3 with Windows 10