B777-300
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 171; Flight Crew Total 15402; Flight Crew Type 14288
Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Fuel Issue
Flight Crew Diverted; Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft; Manuals
About 5 minutes before push; we had this FA (Flight Attendant) who said she was the safety checker. One of her checks is to check for stowaways in the OFCR (Overhead Flight Crew Rest.) When she was up there she checked the smoke detectors and the one that was in airplane right bunk was flashing red. It was not flashing red when I checked my bunk one hour prior to push. So we took an hour and a half delay to get a new smoke alarm installed. An hour and a half later; we depart and just out of 10;000 the Purser calls and tells us everything; but lights are out in aft galley. We call [Maintenance Control]. Captain tells us (I was one of 2 IROs [International Relief Officers]) to go ahead on break; so we leave. I did not want to sleep if the cockpit would need me.After approximately 15 minutes waiting to hear something from the cockpit; the other IRO decided to go to sleep. I left the OFCR to give him some privacy. When I went down; there was an FA waiting to go into the cockpit; so I slipped in. I knew they could use the help. Talking to aft galley; Dispatch; [Maintenance Control]; ATC. They had asked the FA to come up and give firsthand knowledge while they were talking to [Maintenance Control]. I took over answering the handset calls. [Maintenance Control] had us try the Emergency switch; CBs (circuit breakers); and then the Cabin/Utility switch in cockpit to no avail.Then a fuel imbalance EICAS pops up while we were feeding out of Center tank; approximately one and one half hour minutes into flight. I work the checklist with the Captain. We get from about 3.9K out of balance to 2K out of balance and complete the checklist since we are still working the galley power problem. Dispatch wanted us to press on for [our destination] even though we already took off an hour late and would have no food except midflight snack for the now [14-plus hour] flight. Thinking about Diabetics; people who need food for medicine; and turning them hypoglycemic. Would the food spoil before we could get open ovens and cook 280 meals in ovens designed to cook 30 meals? We said; 'you could fix and re-crew if we go to [alternates].' They didn't like that idea and we were headed back to [ZZZ; our departure airport].Started to use the Diversion Planning Guide when approximately 10 minutes later [Maintenance Control] tells us try the SMOKE/AIRFLOW guarded button in the OFCR and OFAR. It did not have anything illuminated in it. What? So I go back and push the button and it worked. So; now we have a good airplane; but not enough gas to get to [our original destination]. Still on the line with Dispatch we inquire how about [a couple alternate options] for a re-crew? Dispatch tells us there are no crews available. Further discussion with Dispatch tells us to continue back to [our departure airport]. Now comes the discussion of dump or land overweight. Captain was asking the ramifications of each to Dispatch and Dispatch put the decision on the Captain without giving any good insight for the follow on for the airplane or Canada getting fuel dumped on them. We decided for safety and landing on a shorter runway at ZZZ to dump.We go to dump at Flight Level 250 while coordinating with Center. While running the checklist; when we turn the jettison pumps on; the right one is inoperative! We recycle valve to no avail. Since we are pumping out of Center Tank only; it took about 10 minutes longer to get to MLW (Max Landing Weight) plus the 13K we estimated to get back to ZZZ so we would land at MLW and avoid unnecessary fuel loss. We ended up dumping around 102K of fuel. The Captain has the paperwork that has lat/long; fuel; weather; Fl. In the middle of dumping fuel; the Fuel Imbalance EICAS comes back and is about 6K out of balance. We finish the Jettison checklist and run the Fuel Imbalance checklist again. Get it back within 2K as we're getting started descent on the arrival. By this time; the other IRO has returned and looks up the info in the Systems section of FM (Flight Manual.) He finds a note there about 'pressing the OFCR SMOKE/AIRFLOW button can restore power to the aft galley!' Why wouldn't [Maintenance Control] know this? I am sorry; but I do not have the FM memorized; and I never remembered that note when learning about the 777-300 when we started flying them. An obscure switch for galley power if you ask me. We land back at ZZZ without any more incidents. The crew completed the debrief using the issued debrief card. As we were leaving the cockpit; we were met by the Chief Pilot ZZZ and another Flight Office pilot. Captain debriefed them and we were released from duty and the trip.
B777 First Officer reported partial electrical failure; fuel imbalance indications; and jettison pump failure; resulting in return to airport.