Is this a motorized system? Start by going to
www.sadoun.com and folloowing links to
installation help then the appropriate section for your system (motorized or nonmotorized). 121 is an Echo bird so it is far stronger than 123 when trying to pick up signal. With that said 121 is also a bit higher in the sky and a bit east. So if you ahve 121 you need to move 2 degrees to the west and down a hair. If you are motorized all bets are off! You need to start back from square one with zeroing in on your true south sat.
Steve