What was found
FLIGHT 2380. DURING ENGINE START, WE HAD AN APU FAIL WITH A LOUD BANG. SPARKS WERE SEEN COMING OUT OF THE APU, SMOKE AND SPARKS WERE SEEN COMING OUT OF THE #1 ENGINE, POWER WAS TEMPORARILY LOST THRU THE PLANE. RETURNED TO THE GATE REMOVED FROM SERVICE. PERFORMED GVI OF APU AND #1 ENGINE NO DEFECTS FOUND. ATTEMPTED START OF APU, START FAILED. PERFORMED 2 STARTS OF #1 ENGINE NO DEFECTS OR SMOKE NOTED. APU PLACED ON MEL 49-00-00. RETURNED TO SERVICE.