What was found
NR 2 GENERATOR DROPPED OFF THE LINE. APU SWITCHED AND POWER RESUMED NORMAL. APPROX 4 MINUTES LATER NR 2 GENERATOR BUS POWER DROPPED OFF THE LINE AND IT WOULD NO LONGER POWER. FLIGHT ATTENDANT REPORTED A LOUD GRINDING NOISE AND WHAT THEY DESCRIBED AS A ENGINE BACKFIRING. APU GEN BUS VOLTS AND FREQUECY WERE NORMAL, APU AMP GAGE WAS FLUCTUATING. SHUT DOWN APU AND DIVERTED TO BHM. REMOVED AND REPLACED NR 2 ENGINE GENERATOR CONTROL UNIT, OPS CKD GOOD PER MM.