A federal mediator has stepped in, and talks are going on around the clock, but there is still no end in sight for the Charlotte Symphony musicians’ strike. This weekend’s season-opening concerts have been cancelled, and no one involved in the talks seems to think a breakthrough is near. At issue is the orchestra’s desire to cut back the number of paid weeks per year for which it contracts its musicians, in order to make up a $645,000 deficit. The musicians claim that the deficit, the orchestra’s first in seven years, is an aberration, and that no salary cuts should be necessary. Musicians in the Charlotte Symphony currently make $31,200 per year. The proposed cut would knock them back to $28,860.