A MECHANIC REPORTS THAT NUMEROUS OVERHEAD PASSENGER SERVICE UNITS (PSU) WERE INCORRECTLY MODIFIED PER AN ENGINEERING CHANGE ORDER; AND THAT THE OXYGEN GENERATOR DOOR RELEASE MAY FAIL TO OPERATE.

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I WAS ASSIGNED AN ENGINEERING ORDER FOR ACFT X. I TURNED OVER THE WORK ON THE ENGINEERING ORDER TO PERSON 1; WHO STATED THAT HE WAS FAMILIAR PERFORMING THIS ENGINEERING ORDER. MECHANIC; PERSON 2; INFORMED ME THAT 6 OF THE PSU'S THAT HAD BEEN MODIFIED BY PERSON 3 WERE DONE IMPROPERLY. THE WASHER FOR THE CABLE CAMS HAD BEEN PLACED BETWEEN THE CAM AND COVER INSTEAD OF ON TOP OF THE COVER. THIS CONFIGURATION WOULD CAUSE THE CAM TO BIND DURING AN EMER O2 DROP. I INFORMED MY SUPVR OF THE SITUATION. WE FOLLOWED APPROPRIATE PROCS FOR PERFORMING REWORK OF THE PSU'S IN QUESTION. I THEN REVIEWED THE REMAINING PSU'S ON THE ACFT FOR CONFORMITY. I SUGGESTED THAT A REVIEW OF ACFT RECORDS RELATING TO THIS ENGINEERING ORDER BE PERFORMED AND A REINSPECT OF AFFECTED ACFT BE PERFORMED.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE ORIGINAL RELEASE PIN THAT IS PULLED TO ALLOW THE OXYGEN CANISTER FIRING PIN TO ACTIVATE THE CHEMICAL OXYGEN GENERATOR ON THE B737-700 ACFT IS BEING REPLACED PER AN ENGINEERING ORDER WHICH HE BELIEVES CAME FROM A SERVICE BULLETIN. THE OLD FIRING PIN WAS MADE FROM A VERY SOFT MATERIAL; SIMILAR TO AN OLD METAL COAT HANGER. THIS PIN WAS SUBJECT TO SCORING OF THE RELEASE PIN; ESPECIALLY FROM THE NORMAL VIBRATION AND OVERHEAD MOVEMENT OF THE LUGGAGE BINS. THIS SCORING OF THE RELEASE PIN CAUSED DIFFICULTY IN GETTING THE PIN TO COME OUT WHEN THE MASKS WERE DROPPED. AS A RESULT; EVEN THOUGH A PASSENGER WAS PULLING ON THE RELEASE LANYARD; WHICH IS ATTACHED TO ALL THE MASKS IN EACH OVERHEAD PSU; THE PIN WOULD NOT COME OUT AND NO OXYGEN WOULD BE AVAILABLE TO THAT ROW OF PASSENGERS. REPORTER STATED THE MODIFICATION INCLUDED A NEW RELEASE PIN MADE FROM A HARDER MATERIAL WITH A NITRATE COATING THAT IS VERY SLICK. THESE RELEASE PINS OPERATE VERY SMOOTHLY. REPORTER STATED THERE ARE ALSO CAMS AND WASHERS AND A SHOULDER BOLT BEING REPLACED; AS PART OF THE MODIFICATION; TO PROVIDE A SMOOTH OPENING OF THE OXYGEN CANISTER COMPARTMENT DOOR TO ALLOW THE MASKS TO DROP. SOME OF THE MODIFIED PSU'S HAVE BEEN FOUND WITH THE WASHER FOR THE DOOR CABLE CAMS PLACED BETWEEN THE CAM AND COVER; INSTEAD OF ON TOP OF THE COVER. THIS CONFIGURATION WOULD CAUSE THE CAM TO BIND; NOT ALLOWING THE OXYGEN DOOR TO DROP DURING AN EMERGENCY. IN THAT CONDITION; NO OXYGEN WOULD BE AVAILABLE TO THAT ROW OF PASSENGERS.