how can I fix the alternator on a 150 cc scooter[sunl]?

The alternator is behind the flywheel on the side of the engine. Look through the flywheel and you'll see some wire coils. This is the alternator, which generates AC or alternating current. However your scooter needs DC or direct current and this is done by a device called the rectifier - usually a square plastic box mounted somewhere. Go over the wiring and connections very carefully looking for tears or splits before condemning any component.

John
January 2008