As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IAH - FLT 3969 - PILOT REPORTED THAT SMOKE WAS NOTED FROM THE 90VU RACK FOLLOWED BY THE LOSS OF THE NR 1 ACW GENERATOR. THE AIRCRAFT RETURNED TO IAH WITHOUT INCIDENT. MAINTENANCE REMOVED AND REPLACED THE NR 1 ACW GENERATOR CONTROL UNIT. THE AIRCRAFT OPERATIONALLY CHECKED GOOD AND WAS RETURNED TO SERVICE. (X)