B737-300 EMER EVACUATION SLIDE DEPLOYED AFTER GATE ARRIVAL.

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AFTER XING THE RWY AND TAXIING BACK TO OUR GATE; I ELECTED TO START THE APU TO PREPARE FOR A QUICK TURN. ONCE THE APU WAS UP TO SPD; WE MADE SEVERAL UNSUCCESSFUL ATTEMPTS TO XFER ELECTRICAL PWR TO THE APU GENERATOR. I INFORMED MY FO THAT WE WOULD USE GND PWR AT THE GATE UPON ARR AND TO WRITE UP THE DEFECT SO MAINT COULD TROUBLESHOOT. ACFT RECEIPT AT THE GATE WAS UNEVENTFUL AND THE R ENG WAS SECURED UPON SETTING THE PARKING BRAKE; BUT THE ACFT WOULD NOT ACCEPT THE GATE PWR EITHER. AFTER 2 UNSUCCESSFUL ATTEMPTS WITH GATE PWR; I CONTACTED OPS AND ASKED FOR A GND PWR CART. OPS SAID THEY WOULD GET ONE ASAP. AT THIS TIME WE RECEIVED AN ACARS MESSAGE FROM MAINT ASKING US TO PULL AND RESET A COUPLE OF CIRCUIT BREAKERS BEHIND THE FO'S SEAT TO RESET THE GND PWR SYS. WE DID NOT COMPLY AS THE EVENTS IN THE CABIN DESCRIBED BELOW BEGAN TO TAKE PLACE. AS WE STOPPED AT THE GATE; I NOTICED THE JETBRIDGE MOVING TOWARD THE ACFT WITH AN AGENT AT THE CTLS. A FEW MOMENTS LATER; THERE WAS A KNOCK AT THE COCKPIT DOOR. THE PURSER ADVISED THAT THERE HAD BEEN A PARTIAL SLIDE DEPLOYMENT AT 1L. STILL DEALING WITH THE GND PWR PROB; I ASKED MY FO TO KEEP THE PAX CLR OF THE AREA AND INVESTIGATE. UPON HIS RETURN TO THE COCKPIT; HE INFORMED ME THAT THE SLIDE PACK WAS LAYING PARTIALLY IN THE FORWARD ENTRYWAY; THE DOOR WAS CLOSED AND THE GIRT BAR WAS DETACHED FROM THE THRESHOLD (DISARMED). MY FO SUGGESTED THAT I INVESTIGATE THE SLIDE RAFT PROB. I ASKED HIM TO RETURN TO HIS SEAT AND GUARD THE BRAKES UNTIL WE COULD GET THE ENG SHUT DOWN. AFTER HE WAS SEATED; I STEPPED TO THE BACK TO FIND THE SCENE EXACTLY AS HE HAD DESCRIBED: SLIDE RESTING IN THE FORWARD ENTRYWAY; DOOR CLOSED; GIRT BAR SITTING ON THE GND. I LOOKED THROUGH THE VIEW PORT AND SAW 2 STATION PERSONNEL -- THE ONE WHO INITIALLY MOVED THE JETBRIDGE; AND ANOTHER AGENT. SEEING THAT THE DOOR WAS NO LONGER ARMED; I CRACKED OPEN THE DOOR TO SPEAK TO THE AGENTS. THE AGENT INFORMED ME THAT A PIECE OF THE RAFT WAS WEDGED BTWN THE BRIDGE AND THE DOORWAY AND THEY WERE GOING TO RETRACT THE JETBRIDGE TO REMOVE THE ITEM. AT THIS POINT; I TURNED TO SPEAK TO THE PURSER AND THE SLIDE DEPLOYED INSIDE THE ACFT. THE PURSER AND I RETREATED INTO THE FIRST CLASS CABIN AND THE RAFT INFLATED; THEN RUPTURED AND DEFLATED. AFTER ASSURING THAT NO ONE WAS INJURED; I RETURNED TO THE COCKPIT AND INFORMED THE PAX OVER THE PA WHAT HAD HAPPENED AND THAT THE SIT WOULD SOON BE RESOLVED. SHORTLY THEREAFTER; THE GPU ARRIVED; WE SHUT DOWN THE ENG AND COMPLETED OUR CHKLISTS. I RETURNED TO THE FORWARD ENTRY AND ASSISTED THE GND PERSONNEL IN REMOVING THE RAFT ALLOWING OUR PAX TO DEPLANE. AFTER CLRING THE ACFT AND SPEAKING WITH THE STATION SUPVR; WE DEBRIEFED THE CABIN CREW; AND REVIEWED THEIR MANUAL TO ENSURE THEY FOLLOWED THE CORRECT PROC WITH THE DOOR. THE PURSER STATED THAT SHE HAD NOT YET DISARMED THE DOOR AND CRACKED IT WHEN THE AGENT ATTEMPTED TO OPEN IT. SHE STOPPED HER FROM DOING SO BUT NOT UNTIL THE DEPLOYMENT PROCESS HAD STARTED. THE STATION AGENT WHO OPENED THE DOOR HAD VACATED THE AREA AND COULD NOT VERIFY WHAT THEY HAD SEEN OR DONE. IN MY ESTIMATE; 1 OF 2 THINGS OCCURRED TO CAUSE THIS EVENT: 1) THE GATE AGENT OPENED A DOOR THAT WAS STILL LATCHED AND ARMED; OR 2) THE PURSER CRACKED THE DOOR BUT FAILED TO DISARM IT. IN EITHER EVENT; THE PURSER STOPPED THE AGENT FROM OPENING THE DOOR FURTHER. THIS PREVENTED AN IMMEDIATE DEPLOYMENT INTO THE JETBRIDGE. WHAT CAUSED THE DELAYED DEPLOYMENT; I CANNOT SAY FOR SURE. WHEN MY BACK WAS TURNED FROM THE DOOR; THE AGENTS OUTSIDE WERE ATTEMPTING TO MOVE THE JETBRIDGE AND NO ONE WAS TOUCHING THE SLIDE PACK ON THE INSIDE WHEN IT INFLATED. THE AGENT LATER SHOWED ME THE ITEM THAT WAS WEDGED BTWN THE PLANE AND BRIDGE. TO ME; IT APPEARED THAT IT WAS THE ACTIVATING MECHANISM FOR THE SLIDE THAT WAS CONNECTED TO THE CTR OF THE GIRT BAR BY A SMALL CHAIN. DURING THE ENTIRE EVENT; THERE WAS A CONSIDERABLE AMOUNT OF NOISE IN THE JETBRIDGE SINCE WE WERE UNABLE TO SECURE THE #1 ENG UNTIL THE PWR CART ARRIVED. THIS MAY HAVE CONTRIBUTED TO THE EVENTS THAT TOOK PLACE. I INFORMED THE STATION MGR AND PURSER THAT I WOULD BE FILING A RPT AND ADVISED THEM TO FOLLOW THEIR INDIVIDUAL DIRECTIVES REGARDING SUCH INCIDENTS. AFTER CONFERRING WITH MAINT AND THE DUTY MGR; WE ELECTED TO DEFER THE APU GENERATOR AND SLIDE RAFT. THE FO AND I THEN FERRIED THE ACFT FOR REPAIRS.