CAPT OF AN MLG DEPARTED WITH THE PAX PA SYS INOP AND THE ALTERNATE 'BULL HORN' ALSO MALFUNCTIONING.

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I WAS SCHEDULED TO DEADHEAD ON THIS PARTICULAR FLT FROM ATL TO EWR. 20 MINS BEFORE SCHEDULED DEP TIME; I WAS PAGED AND TOLD TO CALL CREW SCHEDULING. I WAS ASKED TO THEN FLY AS CAPT ON THAT PARTICULAR FLT SINCE THE REGULAR SCHEDULED CAPT'S WIFE HAD BECOME ILL AND HE NEEDED TO RETURN HOME. 'NO PROB' I SAID. BY THE TIME I CHANGED INTO UNIFORM; OBTAINED THE NECESSARY PAPER WORK; AND SEATED MYSELF IN THE COCKPIT; IT WAS 5 MINS PRIOR TO PUSH. IT WAS THEN THAT I FOUND OUT THAT SINCE THIS PARTICULAR ACFT HAD JUST COME FROM A REWORK FACILITY; THAT NO CATERING SUPPLIES WERE ON BOARD. NO BEVERAGES (INCLUDING COFFEE) OR SNACKS AND NOTHING COULD BE FOUND PRIOR TO TAKING A 1 HR DELAY. ADDITIONALLY; ONE OF THE LCL HOME TOWN CARRIERS CANCELED A FLT TO EWR AND SENT ALL THEIR PAX OVER WITH NO ADVANCE NOTICE. THE FLT WAS NOW OVERSOLD. NEXT; THE FLT ATTENDANT INFORMED ME THAT THE CABIN PA VOLUME WAS VERY WEAK AND HARD TO HEAR. IT'S NOW SCHEDULED DEP TIME WITH EVERY SEAT OCCUPIED WITH EVERYONE AWARE THAT NO BEVERAGE OR SNACK WILL BE SERVED. DO I THEN INFORM THE PAX THAT WE WILL TAKE A MAINT DELAY TO LOOK OVER THE PA SYS? NO; LET'S MAKE THEM HAPPY AND ARRIVE ON TIME. AFTER PUSHBACK AND ENG START; THE FLT ATTENDANT THEN INFORMS ME THAT THE PA VOLUME IS SO LOW THAT IT CANNOT BE HEARD. MEL SAYS WE CAN DISPATCH WITHOUT IT; SO WE PROCEED ON WITH ALTERNATE MEANS. AFTER TKOF; I THEN FIND OUT THAT ONE OF THE MEGAPHONES; WHICH PREFLT CHKED OK; WAS ALSO NOT WORKING PROPERLY. PLACING TOO MUCH EMPHASIS ON 'ON TIME' INFLUENCED MY BETTER JUDGEMENT TO DELAY THE FLT AND HAVE MAINT CHK OUT A PROB. PROBS DON'T FIX THEMSELVES; THEY ONLY GET WORSE AND COMPOUND. FORTUNATELY; THIS DID NOT DEVELOP INTO ANY SERIOUS PROBS; BUT THIS TYPE SCENARIO COULD FOR SOMEONE ELSE WITH A DIFFERENT SET OF PROBS. MY LATE ARR TO THE COCKPIT CERTAINLY DIDN'T HELP MATTERS. HAD I BEEN THERE SOONER; I WOULD NOT HAVE HESITATED CALLING MAINT. I LET BEING 'ON TIME' CLOUD MY JUDGEMENT OF SAFETY FIRST. FIX THE PROBS EARLY BEFORE THEY GET WORSE AND UNFIXABLE.