Preview song problems on DDJ-S1

Hello, I've some problems on preview song on my DDJ-S1.

I've already change my HPJB assy, but its not the problem.

My preview song is very strange, I've no bass, and the quality off the song is bad.

I can precise when I put the "select head" on CUE the song is bad and when its on the MASTER it was ok.

Another thing, when I put the level sound off headphone more higher on "CUE" selected, the song is bad as before.

I don't know if the problem was from the Main ASSY or from the JACK ASSY or maybe the DJMB Assy.

Please help me, im in trouble..

(sorry for my English, I'm French)

Thks.