B757 ENRTE SLC NEAR ONL ENCOUNTERED SMOKE IN THE CABIN FROM THE PAX ANNOUNCE SYS. FO UNABLE TO PULL CANNON PLUG ACCOUNT PLASTIC COVER. MECH ON BOARD WAS ABLE TO PRY OFF COVER AND PULL PLUG. HAD DECLARED EMER AND CANCELED; PROCEEDED TO DEST SLC.

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ENRTE TO SLC ACR XYZ IN THE AREA OF THE ONL VOR (ZDV); THE PRERECORDED PAX ANNOUNCEMENT SYS OVERHEATED AND STARTED TO SMOKE. AN EMER WAS DECLARED AND AN ARPT DIVERSION WAS BEGUN. THE COPLT WAS ABLE TO REMOVE THE PLASTIC COVER BUT COULD NOT UNHOOK THE CANNON PLUG. A NON-REVENUE MECH CAME FORWARD AND WAS ABLE TO UNHOOK THE WHOLE SYS BY REMOVING PWR. THE SMOKE AND HEAT STOPPED SO WE CANCELED THE EMER. WE CONTINUED ON TO SLC WITHOUT FURTHER PROBS. THE PAX WERE NOT AWARE OF THE SHORT DIVERT. THERE NEEDS TO BE AN EASIER WAY FOR THE CREWS TO UNHOOK ELECT FROM THIS SYS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED COMPANY HAD INSTALLED A PLASTIC PANEL OVER THE SYS TO PREVENT PRIVATE RECORDINGS TO BE INSERTED. AS A RESULT THE FO HAD NO WAY OF GETTING TO THE CANNON PLUG. THE MECH HAD A PRYING TOOL THAT PERMITTED HIM TO PRY OPEN THE PLASTIC COVER AND PULL THE CANNON PLUG FROM THE UNIT. THE UNIT HAD BEEN OPERATING FROM THE TIME OF ACTIVATION PRIOR TO TKOF. NO SEPARATE CIRCUIT BREAKER IN THE COCKPIT FOR THE SYS. SMOKE CLRED FROM THE CABIN RAPIDLY. SYS WAS FOUND TO BE BADLY BURNED ON ARR AT SLC. CAPT HAD RECEIVED NO TRAINING ON THIS EQUIP.