Necchi 524 FB Zigzag

Question

I have a Necchi 524 FB, the zigzag only works if you pull up on the knee of the guide that floats along the bottom of the cams. It seems like a spring should do that, but no spring in sight. If you do nothing, the lever under the cams does come up far enough to follow the pattern of the cam. Is there a exploded view online I could look at?Molly