A MECHANIC QUESTIONS TWO OUTSIDE MAINT CONTRACTORS WHO WERE ON A B747-400 WORKING THE CABIN INFLIGHT ENTERTAINMENT SYSTEM AND SWAPPING UNITS WITHOUT ANY PAPERWORK OR DOCUMENTATION.

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JUN/XA/08 AT APPROX XA00; I NOTICED 2 PEOPLE WALKING TO ACFT X ON GATE X. THESE PEOPLE HAD THE UNIFORMS OF COMPANY Y MAINT AND ONE OF THEM CARRIED WHAT APPEARED TO BE AN ACFT ELECTRONIC PART ONTO THE ACFT. WHILE I WAS COMPLETING THE PREDEP CHK; THE GATE PWR FAILED AND I HAD TO RECYCLE THE GND PWR TO SUPPLY PWR TO THE ACFT. WHEN I EXITED THE ACFT; I NOTICED THE 2 COMPANY Y PEOPLE WORKING ON A PANEL THAT APPEARED TO BE AN INTERFACE UNIT FOR THE PAX SYS IN THE MID 2 GALLEY AREA. I FINISHED THE PREDEP CHK AND WENT TO FINISH MY PAPERWORK AND COMPUTER ENTRIES. PRIOR TO SIGNING FOR THE CHK; I REVIEWED PAPERWORK AND NOTICED NO REFS TO PAX ENTERTAINMENT SYS BEING WORKED. I WENT BACK TO THE ACFT AND ASKED THE 2 PEOPLE WHAT THEY WERE DOING. ONE OF THE COMPANY Y EMPLOYEES TOLD ME THAT THEY CHANGED A (SOMETHING) UNIT AND NEEDED TO CHK IT OUT (MY WORDS; NOT HIS). I SAID THAT; YOU ARE STILL WORKING ON THE ITEM; AND HE REPLIED YES. I SAID THAT I DID NOT SEE A WRITE-UP; HE REPLIED THAT THEY HAVE JUST SWAPPED OUT THE UNIT AND THAT IT DID NOT FIX THEIR PROB; AND THAT THE OLD UNIT WAS REPLACED. I SAID THAT THEY NEED A WRITE-UP WHENEVER WORK IS DONE ON THE ACFT BECAUSE A WRITE-UP LETS THE RELEASING MECH KNOW THAT MAINT IS STILL IN PROGRESS ON THE ACFT AND NOT TO RELEASE IT FOR FLT. I HAD ALMOST RELEASED THE ACFT FOR FLT AND WOULD NOT HAVE KNOWN WORK WAS STILL IN PROGRESS WITHOUT A WRITE-UP. THE COMPANY Y EMPLOYEE REPLIED THAT HE WOULD MAKE A WRITE-UP.