A B737-700 VERBAL RPT FROM CREW ON PACK TRIPS WORKED BY TECHNICIAN LEADS TO PRESSURE CONTROLLER REPLACEMENT. ACTUAL PROB WAS L AND R PRE-COOLER VALVE FAILURES.

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ON OCT/SUN/05 APPROX XA00 HRS; THE ZZZ LINE COORDINATOR RECEIVED A RADIO CALL FROM THE CREW OF ACFT X STATING THAT THEY WERE INBOUND WITH A 'PACK PROB.' IT WAS RECORDED IN THE MAINT RPT AND PASSED ON TO ME AS SUCH. UPON ARR; THE CAPT VERBALLY RPTED A 'R PACK TRIP' AT ALT. THIS CAUSED A DROP IN CABIN PRESSURE. THE CREW INCREASED THE L PACK SETTING TO COMPENSATE AND PREVENT A SUDDEN LOSS OF CABIN PRESSURE AS THEY BEGAN THEIR DSCNT. WHILE IN DSCNT; WITH THROTTLES SET AT 'IDLE' PWR; THE CAPT STATED THAT THERE WAS A L BLEED TRIP; SUCCESSFULLY RESET; FOLLOWED BY DUAL BLEED TRIPS WHICH WOULD NOT RESET FOR APPROX 2 MINS; AT WHICH TIME THE PACKS WERE CYCLED 'OFF;' THE TRIPS RESET; AND PACKS CYCLED 'ON' AGAIN. AT THAT TIME; THEY WERE ABLE TO REGAIN CTL OF PRESSURIZATION. THIS SCENARIO WAS RELATED TO ME 'VERBALLY' NO LESS THAN 2 TIMES BY THE CAPT. IN ADDITION; THE CAPT REQUESTED OIL SVC FOR BOTH ENGS AND RPTED THE FORWARD GALLEY COFFEE MAKER 'INOP.' THESE ADDITIONAL ITEMS WERE PASSED TO OTHER MEMBERS OF THE MAINT TEAM; ALLOWING ME TO FOCUS ATTN ON THE ORIGINAL DISCREPANCY. THERE WAS NO RPT BY THE CREW OF ANY ASSOCIATED LOSS IN DUCT PRESSURE DURING THIS EXCHANGE; THEREFORE; NO REASON TO SUSPECT ANY BLEED PROB EXISTED OUTSIDE THE LOSS OF ABILITY TO CTL PRESSURIZATION DURING THE DSCNT. THE CABIN PRESSURE CONTROLLERS USED IN THE FLEET HAVE LONG BEEN THE SUBJECT OF RELIABILITY ISSUES. SO MUCH SO; THAT THERE IS A PROGRAM CURRENTLY IN PLACE TO REMOVE THEM FROM CERTAIN ACFT; DOWNLOAD THE HISTORY AND FORWARD THIS INFO TO COMPANY MAINT HEADQUARTERS FOR REVIEW AND/OR ASSESSMENT OF THE UNITS WHILE IN SVC. KNOWING THIS; I IMMEDIATELY SET ABOUT PERFORMING FRONT FACE BITE CHKS ON THE CABIN PRESSURE CONTROLLERS; #1 AND #2; TO VERIFY SYS INTEGRITY. THE #2 CONTROLLER TESTED 'SYS OK.' UPON ATTEMPTING TO ACCESS BITE ON THE #1 CONTROLLER; THE DISPLAY FLASHED AN UNRECOGNIZABLE SEQUENCE OF DASHED LEGS. IN LESS THAN 1 SECOND; THE DISPLAY EXTINGUISHED; THE UNIT PWRED 'OFF' AND WOULD NOT ENTER THE BITE CHK OR SHOW ANY SIGNS OF PWR. SUBSEQUENT ATTEMPTS TO ACCESS THE BITE MENU PRODUCED NO RESULTS. THIS WAS SEEN AS A 'HARD FAILURE' AND PROMPTED THE REPLACEMENT OF THE #1 CABIN PRESSURE CONTROLLER. CIRCUIT BREAKERS FOR THE PRESSURE CTL SYS WERE INTACT. AFTER RPTING MY FINDINGS TO THE CAPT; I REQUESTED HE WRITE A LOG PAGE DISCREPANCY WHILE A NEW UNIT WAS BEING INSTALLED. HE ASKED IF I WOULD LIKE TO WRITE THE DISCREPANCY OR SHOULD HE? I REQUESTED THE CAPT ENTER THE DISCREPANCY; AS IT HAD OCCURRED; IN HIS OWN WORDS. UPON INSTALLATION OF THE #1 CABIN PRESSURE CONTROLLER AND A SUCCESSFUL BITE; THE LOG PAGE (REF X) WAS COMPLETED WITH THE ACTION TAKEN TO ADDRESS THE PROB; DURING WHICH TIME I RECEIVED A RADIO CALL TO VERIFY OIL SVC QUANTITIES. THESE WERE ADDED AS THE 'ROTABLE' TAGS WERE HANDED TO ME TO COMPLETE THE PAGES FOR THE 'PACK PROB' AND THE FORWARD GALLEY COFFEE MAKER (REF X). AFTER HEARING OF PRESSURIZATION PROBS OCCURRING ON AN ACFT; APPROX 6 HRS LATER; AND RECOGNIZING THE FINAL DEST AS THAT OF ACFT X; CONVERSATIONS WITH OTHER MAINT TEAM MEMBERS CAUSED ME TO MORE CLOSELY EXAMINE LOG PAGE (REF X). THAT IS WHEN I DISCOVERED THE DISCREPANCY WRITTEN DID NOT PRECISELY MATCH THAT OF THE 'VERBAL' DISCREPANCY I WAS TASKED WITH EARLIER; AS ENTERED IN THE MAINT RPT; VIA RADIO OR WHILE BEING ADDRESSED BY THE CAPT. HAD THE 'WRITTEN' DISCREPANCY BEEN AVAILABLE DURING INITIAL EVALUATION OR READ MORE THOROUGHLY DURING THE 'SIGN-OFF' PHASE; DIFFERENT CONCLUSIONS COULD HAVE LED TO FURTHER TROUBLESHOOTING AND/OR REPAIRS. I RECOGNIZE THE IMPORTANCE OF THIS PHASE AND SHALL ENDEAVOR TO PREVENT ANY OVERSIGHT IN THE FUTURE. THE PROB WAS RPTED AGAIN AND PROPER REPAIRS EFFECTED WITHOUT INCIDENT; AS SEEN IN THE ACFT LOG (REF Y). THROUGH FURTHER RESEARCH; IT HAS SINCE BEEN MADE KNOWN THAT THE 'FAILURE RATE FREQ' OF PRE-COOLER VALVES ON THE -700 FLEET; WHICH CAN CAUSE BLEED TRIPS; IS AKIN TO THE 'FAILURE RATE FREQ' OF PRESSURE CONTROLLERS IN THE PAST. WOULD RECOMMEND AN ALERT OR OTHER SUCH NOTAMS; CONCERNING THE POSSIBILITY OF A 'DUAL' FAILURE OF THESE COMPONENTS AND THE HISTORY OF SUCH IN THE FLEET. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAPT VERBALLY BRIEFED THE RPTR TWICE ON THE PACKS TRIPPING AND THE LOSS OF PRESSURIZATION; BUT NEVER MENTIONED LOSS OF ENG PNEUMATIC BLEED PRESSURE. THE PRESSURIZATION CONTROLLERS WERE RPTEDLY SUSPECT AND WERE CHKED FIRST. THE RPTR STATED THE PRESSURIZATION CONTROLLERS ARE A CHRONIC PROB AND IN THIS CASE #2 TESTED OK; BUT #1 HAD A HARD FAULT AND WOULD NOT ENTER THE SELF-TEST MODE. THE RPTR INDICATED THE #1 CONTROLLER WAS REPLACED AND TESTED OK AND THE AIRPLANE WAS DISPATCHED. AT THIS POINT IN TIME THE RPTR INDICATED HE/SHE LOOKED AT THE ACTUAL LOG PAGE COPY AND NOTED THE DIFFERENCE BTWN THE VERBAL RPT AND THE WRITTEN RPT WHICH INDICATED A BLEED DUCT PRESSURE LOSS; ADDING THIS WOULD HAVE POINTED NOT TO A PRESSURIZATION PROB BUT A BLEED FAILURE. THE RPTR SUGGESTED THE MAJOR CAUSE OF A BLEED FAILURE ON THIS AIRPLANE IS THE PRE-COOLER VALVE WHICH IF UNABLE TO CTL THE BLEED AIR TEMP TO 400 DEGS THEN IT TRIPS THE BLEED SYS. THE RPTR BELIEVES THE PRE-COOLER VALVE FAILURES ARE DUE TO ITS 12 O'CLOCK HIGH HEAT AREA LOCATION ON THE ENG. THE RPTR STATED 6 HRS LATER THE SAME AIRPLANE RPTED PRESSURIZATION PROBS DUE TO ENG BLEED TRIPS.