Maintenance Airframe; Maintenance Powerplant; Maintenance Avionics
Communication Breakdown; Troubleshooting; Situational Awareness
Aircraft Equipment Problem Less Severe
Aircraft Aircraft Damaged; General Maintenance Action
Aircraft; Equipment / Tooling; Human Factors
I replaced a previously broken External Power receptacle pin per the Maintenance Manual (M/M). This pin was subsequently broken again several days later (please see aircraft history). These pins break frequently due to their design. They are mounted by a small diameter threaded area which is a weak spot relative to the diameter of the pin. Also the External Power cord receptacle housing is shallow and does not support the Power Cord well when it is connected.
Reporter stated the External Power Panel (P19) receptacle electrical pins can be removed and replaced from outside of the B737-800s; using an Allen wrench (key) that is inserted into the center; at the end of each exposed pin; and back-screwing the pin out. He suspects the same design exists on the  B737-700/-900 NexGen aircraft. The copper pins are machined down to be narrower (smaller diameter) at the end that screws into the receptacle base.  That design is different than the older series B737s that required a Technician to open-up a panel in the Nose wheel well; right; forward sidewall tunnel in order to access the larger; thicker diameter pins that are secured with a locking nut. Reporter stated connecting and disconnecting the External Power cords contributes to the newer designed pins breaking frequently and generally at the same lower aft pin location; which is one of the larger diameter pins. Sometimes a pin breaks off just above the threaded section that screws into the receptacle base. When that happens; Technicians have to use a flat-head screwdriver and hopefully push in and twist the remaining piece of copper pin out. Because the External Power Panel receptacle housing is also rather shallow; the weight of the External Power cord can put a stress load on the pins. Broken pins cause electrical power drop-offs requiring APU operation to supply electrical power for the aircraft at the gate; using more fuel.
A Line Avionics Technician reports their B737-800 NexGen aircraft External Power Panel (P19) receptacle has redesigned electrical pins that break more frequently; causing External Power drop-offs; increase use of their APUs and fuel burn to supply electrical power for their aircraft at the gates.