Narrative:

Aircraft had an MEL for an hgs (heads up guidance system) fault light with several faults. Aircraft downgraded to CAT I. I troubleshot and found the most likely problem was a deu (drive electronics unit). I tried one per the hgs manual but it did not fix the problem. I tried several other parts in the system; all per the hgs maintenance manual; all no help. I ordered another deu because I thought for sure that was the problem; but this one did not fix the problem. Departure time for the aircraft was on the hour so the decision was made to leave it on MEL. I was quickly trying to close all my access and get paperwork straightened out. In the east&east compartment there were 3 deu's. As a habit I always leave the serviceable tag on the new unit until I permanently install it. I took the 2 deu's I thought were the new ones; and left what I thought was the original installed in the aircraft. The aircraft was already downgraded and the system was inoperative so I did not upgrade to CAT III. I documented my work on a non-routine card. 1 week later co-workers on line routine overnight check had an hgs problem and tried a deu but found the serial numbers were different on the tag and component. My lead who helped me the previous week alerted me; the aircraft was in so we called to verify the serial number installed. My supervisor created a new parts tag so records of the different serial numbers would be known. I believe the cause of the event was me rushing for an on time departure and getting confused over the multiple parts involved. Callback conversation with reporter revealed the following information: the reporter stated the heads up guidance system was being worked and it was believed by reporter the drive electronics unit was at fault. 2 drive electronics units were installed but did not fix the problem. System was again continued deferred but a serviceable unit was left in the electronics rack. This was sorted out when the installed unit was discovered and the serial number did not match the removed unit.

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Original NASA ASRS Text

Title: A B737-700 TECHNICIAN WAS TROUBLESHOOTING THE HEADS UP GUIDANCE SYS AND REPLACED A DRIVE ELECTRONICS UNIT. REPLACEMENT UNIT DID NOT CORRECT PROB. ITEM RE-DEFERRED. NEW UNIT REMAINED ON ACFT WITH NO PARTS DOCUMENTATION RECORD.

Narrative: ACFT HAD AN MEL FOR AN HGS (HEADS UP GUIDANCE SYS) FAULT LIGHT WITH SEVERAL FAULTS. ACFT DOWNGRADED TO CAT I. I TROUBLESHOT AND FOUND THE MOST LIKELY PROB WAS A DEU (DRIVE ELECTRONICS UNIT). I TRIED ONE PER THE HGS MANUAL BUT IT DID NOT FIX THE PROB. I TRIED SEVERAL OTHER PARTS IN THE SYS; ALL PER THE HGS MAINT MANUAL; ALL NO HELP. I ORDERED ANOTHER DEU BECAUSE I THOUGHT FOR SURE THAT WAS THE PROB; BUT THIS ONE DID NOT FIX THE PROB. DEP TIME FOR THE ACFT WAS ON THE HOUR SO THE DECISION WAS MADE TO LEAVE IT ON MEL. I WAS QUICKLY TRYING TO CLOSE ALL MY ACCESS AND GET PAPERWORK STRAIGHTENED OUT. IN THE E&E COMPARTMENT THERE WERE 3 DEU'S. AS A HABIT I ALWAYS LEAVE THE SERVICEABLE TAG ON THE NEW UNIT UNTIL I PERMANENTLY INSTALL IT. I TOOK THE 2 DEU'S I THOUGHT WERE THE NEW ONES; AND LEFT WHAT I THOUGHT WAS THE ORIGINAL INSTALLED IN THE ACFT. THE ACFT WAS ALREADY DOWNGRADED AND THE SYS WAS INOP SO I DID NOT UPGRADE TO CAT III. I DOCUMENTED MY WORK ON A NON-ROUTINE CARD. 1 WK LATER CO-WORKERS ON LINE ROUTINE OVERNIGHT CHK HAD AN HGS PROB AND TRIED A DEU BUT FOUND THE SERIAL NUMBERS WERE DIFFERENT ON THE TAG AND COMPONENT. MY LEAD WHO HELPED ME THE PREVIOUS WEEK ALERTED ME; THE ACFT WAS IN SO WE CALLED TO VERIFY THE SERIAL NUMBER INSTALLED. MY SUPVR CREATED A NEW PARTS TAG SO RECORDS OF THE DIFFERENT SERIAL NUMBERS WOULD BE KNOWN. I BELIEVE THE CAUSE OF THE EVENT WAS ME RUSHING FOR AN ON TIME DEP AND GETTING CONFUSED OVER THE MULTIPLE PARTS INVOLVED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE HEADS UP GUIDANCE SYS WAS BEING WORKED AND IT WAS BELIEVED BY RPTR THE DRIVE ELECTRONICS UNIT WAS AT FAULT. 2 DRIVE ELECTRONICS UNITS WERE INSTALLED BUT DID NOT FIX THE PROB. SYS WAS AGAIN CONTINUED DEFERRED BUT A SERVICEABLE UNIT WAS LEFT IN THE ELECTRONICS RACK. THIS WAS SORTED OUT WHEN THE INSTALLED UNIT WAS DISCOVERED AND THE SERIAL NUMBER DID NOT MATCH THE REMOVED UNIT.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.