ACFT EQUIP PROBLEM DETECTED BY SMELL OF SMOKE. ACFT RETURN LANDS AFTER EMER DECLARED.

Narrative

WHILE CLBING THROUGH 13000 FT TO FL230; THE SENIOR FLT ATTENDANT CAME TO THE COCKPIT AND STATED THAT THE OTHER FLT ATTENDANTS IN THE REAR OF THE CABIN SMELLED AN ELECTRICAL ODOR FROM THE AREA OF THE 3L AND 3R DOORS TO THE AFT OF THE CABIN. NO SMOKE WAS VISIBLE. I WENT AFT AND CHKED THE AREA AND FOUND A STRONG ELECTRICAL BURNING ODOR; BUT NO SMOKE. WHILE CHKING THE CEILING AND LAVATORY AREA; THE SMOKE ALARMS IN THE AFT LAVATORIES WENT OFF. AGAIN; NO SMOKE WAS VISIBLE. BOTH FLT ATTENDANTS IN THE REAR GRABBED FIRE BOTTLES AND PREPARED TO COMBAT A FIRE. NO FIRE BROKE OUT AND NO SMOKE WAS VISIBLE. I ASSIGNED THE FLT ATTENDANTS IN THE REAR TO WATCH THE LAVATORY AREA AND KEEP US INFORMED IF FIRE OR SMOKE DID BECOME APPARENT. I ADVISED THE LEAD FLT ATTENDANT TO SECURE THE CABIN AND PREPARE FOR RETURN AND LNDG AT DTW. AFTER INFORMING THE CAPT OF THE SITUATION; WE DECIDED TO CONTINUE BACK TO DTW SINCE NO SMOKE OR FIRE WAS PRESENT. KALAMAZOO WOULD HAVE BEEN OUR OPTION IF THE SITUATION HAD TURNED BAD. THE SMOKE REMOVAL CHKLIST WAS NOT NECESSARY; ALTHOUGH IT WAS REVIEWED SILENTLY. WE ASKED ATC AND WERE CLRED TO EXCEED 250 KTS BELOW 10000 FT. AN EMER WAS DECLARED. AN UNEVENTFUL AND OVERWT LNDG WAS MADE AT DTW. NO EVAC WAS MADE. THE FIRE DEPT CAME ON BOARD AND INVESTIGATED; AND NO EVIDENCE OF A FIRE WAS FOUND. WE SWAPPED AIRPLANES AND AN UNEVENTFUL TRIP TO LAS WAS COMPLETED. MAINT FOUND THAT A DECODER FOR THE MULTIPLEX SYS IN THE CABIN OVERHEAD HAD SHORTED OUT RESULTING IN THE BURNING OF SOME ELECTRICAL WIRING. A FIRE COULD HAVE RESULTED IF QUICK ACTION HAD NOT BEEN TAKEN. I ALSO FEEL THE CREW WORKED AND PERFORMED VERY WELL TOGETHER AS A RESULT OF THE RECENT COCKPIT RESOURCE MGMNT CLASS AT OUR CARRIER.