Date: 201205
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Light: Night
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Circuit Breaker / Fuse / Thermocouple
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Confusion; Workload; Troubleshooting; Distraction; Fatigue; Situational Awareness
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Illness / Injury
Detector: Person Maintenance
When detected: Other Post aircraft Departure
Result: General Maintenance Action
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: In troubleshooting an IDG problem; I swapped Generator Control Unit (GCU1) with GCU2 on Aircraft X; a B737-700. After changing the Integrated Drive Generator (IDG) and running the engine for the Operational Check; I went on to another problem on this aircraft. The Water Tank was on MEL and needed to be changed. At the end of every night I always check the Electrical Equipment (E/E) doors. Last night I remember closing the E/E door on this plane. That bothered me all day. I came in to work tonight and remembered the GCU troubleshooting. I'm not 100% positively sure that I secured or swapped back the GCU's. Human factor: Last week I called in sick for a cold/flu. I still have this stubborn cold but I came into work this week anyway. I remember that the workload for the night was just two Overnight Checks with a Water Tank change. But Aircraft X came in later [than expected] and I was distracted with having to troubleshoot an IDG problem before changing the [Water] tank. It turned into a very long night. I think if I were not sick that I would have been thinking more clearly. I think I could have avoided this problem all together if I had felt better. Next time I will make sure that I'm physically fit for work.

Callback: Reporter stated he was working a B737-700 aircraft that was scheduled for an Overnight Check with a water tank change. But the aircraft had come in later than expected with an unexpected #2 Engine Integrated Generator Drive (IDG) that had been disconnected in flight. He had swapped GCU1 and GCU2 in the E/E compartment as part of his trouble shooting to isolate the electrical problem; than left the E/E compartment leaving the light on and the access door open; planning to return to unswap the GCUs.Reporter stated the last thing he does before he leaves an aircraft after performing maintenance is to close the E/E door. He noticed the E/E light was still on; but he was not feeling well; was very tired and just never associated the light being on with work he had not completed after changing the # 1 Engine IDG; so he closed the E/E door and went home. The GCUs were repositioned to their proper GCU1 and GCU2 position in the E/E compartment after he notified his Supervisor. No incidents occurred that he is aware of.



Synopsis: A Line Mechanic forgot to reposition Generator Control Unit-1 (GCU1) and GCU2 back to their proper position in the E/E compartment of a B737-700 aircraft. He had swapped the two GCU units during trouble shooting of a # 1 Engine Integrated Drive Generator (IDG) failure.