Systema revolution

[Trojan0803]

Could anyone offer any input into why my revolution gearbox is shooting auto only? Looking over it I can't see what could be wrong but it's my first experience with this set up. I recently changed receivers out and the problem has been apparent since, the gear box dropped in lovely and the first thing I did was change the selector cam to match the original. Still no joy, can they be locked to semi? The site I play is semi only anyway.

Tia