Frantzy dugesclin. Yamaha psr s 770. left voice does not work in acmp mode ?

Hi

I ve got a new psr s770 and have a problem
When i play with a style ,( for example latin bossanova )

Right 1 and 2 work correctly but the left part does not work
I have looked the split point and it is good.

I also try to see balance screen
And see that when the acmp button is on , the " left" light does not go on.
When i switch off the acmp button ( so i dont have the acmp function ) , the left ligt on the balance screen go on and i can hear the left voice.

I had the same problem with my psr s750 for some style but not for all and nevr find an explanation.

Hope Somebody could help me
Thank you for answer.