[Unsolved] Problems with principal output

[laotseu]

Hi.
I have a problem with my principal output. A big breath (shuffle) and a lost of sound power appear.
I checked my Access virus classic rack on other ways of my console (mackie). The problem is still here. I read the manual (the access virus classic desktop) and I didn't find the solution to change the output in the Single Mode. Before checking the electronic, I would like to change output (from the principal to the sub n°1).
Can someone explain me, how to change from the principal output to the sub n°1 ?
Thank You

P.S. Sorry for my english I'm French Access virus user.