The most common cause of generator failure is the lack of excitement. To test the generator, you need to make it to the positive terminal of the battery at 1000 rpm of the engine. Before it is necessary to give the load (turn on lights), otherwise failure may leave the switch and other electronics. If the engine stalls the alternator is not working. The first thing to check was broken if the alternator belt. If the belt is intact, it is likely that he was weaker. Check the belt tension: deflection under force of 10 kgf should be not more than 1 cm belt, may be splattered with oil and slip. In this situation, it needs to be replaced, or at least to wipe with gasoline.If the seat belt is tight, clean and not torn, then check the fuses of the field winding. It is usually sufficient simply to move, and then it will work. This is especially true of domestic classics (VAZ-2105, 2106, 2107), which is mounted fuse is weak. If after the performed operation the generator still does not work, then remove the generator. First, inspect brushes for wear – perhaps they need to be replaced. You should also pay attention to the slip rings. If they are dirty, clean them. Now re-check the generator for proper operation. If he does not submit signs of life, arm yourself with tester and check the chain.After all done operations be only two reasons. Either a faulty voltage regulator or the generator. The generator often burn up the rectifier diodes. Each diode should "ping" tester, and if it turns out to be faulty, replace. If all diodes are intact, check the stator winding. This is done with a simple tester, closing them both ends of the winding. If the stator windings are faulty, it can be replaced. However, the stores can get damaged stators, as they are checked in the same way.