Samsung ML 2550 - Manual (Page 213)

P ROGRAMME I NSTALLING P RINTER O PTIONS F.8
6 Tighten the two screws which you removed in Step 4.
7 Replace the control board cover and tighten the two screws.
8 If you purchase the network interface card supporting the
wireless LAN interface, insert the antenna counterclockwise,
as shown.