Started our last run back to the ramp today and it would not shift into gear (forward or reverse). Had throttle control. Was able to pull off the cowling and manually shift it into forward to get back to the ramp. Cables at the motor end looked fine so I suspect it is at the control box end. Acts like the cable is broken or has come detached inside the control box. It's a 1996 Quicksilver 3000. I've been Looking at some videos and diagrams but cannot tell if the control box is repairable or a closed unit. Has anyone had experience repairing this problem?

your on the right track. yes, those cables break, the control box comes apart, and the cables can be replaced

Thanks, I tackled this today. Shift cable was broken about a foot from the motor end. New Telefex throttle and shift cables ordered. Back on the water soon for less than $100.