You cant just swap drives and expect it to work. You need a multimeter to adjust the laser pots correctly then adjust the "Radial Skew" from there. Each drive is unique so if you have never done this it can be a little hard. Shadowknyghts
site Has a laser tutorial that may help you get started. Read the "laser replacement" tutorial very carefully, It can be a slow and time consuming process but you can get through it with a little patience
Good luck.