I need to fix the zig-zag feature on my Brother Boutique 761?

When I set the machine to do the zig-zag stitch, it continues to sew in a straight line.
Also, the needle bar will not stay centered, it's too far to the left. The adjusting screw located to the right of the needle bar will only move it a small amount, and then starts back in the other direction. It appears to be an eccentric.
I can't find a way to adjust the connecting rod as it is in the middle of the machine and not easily accessable.
Any help will be greatly appreciated.