What was found
IAH - FLIGHT 3020, THE CREW REPORTED A BURNING SMELL AFTER ENGINE 1 START. THE AIRCRAFT RETURNED TO THE GATE WHERE MAINTENANCE INSPECTED THE AIRCRAFT AND DETERMINED THE SMELL TO BE CAUSED BY THE APU. THE APU WAS PLACED ON MEL, AND THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE. THE AIRCRAFT SUBSEQUENTLY RETURNED TO IAH WHERE MAINTENANCE REMOVED AND REPLACED THE APU STARTER GENERATOR, OPERATIONALLY TESTED WITH NO DEFECTS, THE MEL WAS CLEARED, AND THE AIRCRAFT WAS APPROVED FOR RETURN TO SERVICE.