MD80 FMS DISPLAY INDICATED A MAP SHIFT. FLT CREW ATTEMPTED TO ALIGN THE IRS AFTER AIRBORNE AND LOST COMPASS INFO. WHILE RETURNING FOR PRECAUTIONARY LNDG; AN ELECTRICAL BURNING ODOR WAS PRESENT IN THE CABIN.

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UPON TAKING THE RWY FOR TKOF WE REALIZED THAT THE MAP DISPLAY WAS SLIGHTLY OFF BUT WE THOUGHT THAT THE MAP WOULD UPDATE AS WE ADDED PWR FOR TKOF. WHEN IT DID NOT UPDATE WE ASKED THE TWR FOR A HDG AND ADVISED THAT WE COULD NO LONGER ACCEPT AN RNAV DEP. WE DEPARTED AND SWITCHED TO DEP. THEY GAVE US A RADIAL TO INTERCEPT. AFTER WE LEVELED INFLT WE DECIDED TO TRY AND ALIGN THE IRS PER THE QRH. WE LOST THE COMPASSES AND COMMAND BARS AT THAT POINT. WE DECIDED TO RETURN TO ZZZ AND NOT CONTINUE. WE INFORMED ATC AND DECLARED AN EMER. THEY TURNED US AROUND AND HEADED US BACK TO ZZZ. SHORTLY AFTER WE TURNED AROUND WE WERE INFORMED BY THE AFT FLT ATTENDANTS THAT THERE WAS A STRONG ELECTRICAL BURNING SMELL IN THE CABIN. WE INFORM ATC OF THE EMER AND RAN THROUGH THE CHKLIST. THE FUMES AT THAT POINT COULD BE DETECTED IN THE COCKPIT. AS WE DSNDED THE FUMES DISSIPATED RAPIDLY. WE RAN THE OVERWT LNDG CHKLIST AND LANDED. CFR EQUIP MET US. NO INDICATIONS OF HEAT. CFR FOLLOWED US TO THE GATE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT THE SYSTEM IS DESIGNED TO UPDATE ACFT POSITION ON TKOF ROLL. THE FLT CREW BELIEVED THAT THIS WOULD OCCUR WHEN THEY BECAME AWARE OF THE MAP SHIFT PRIOR TO DEP. WHEN THE ALIGNMENT WAS ATTEMPTED AFTER AIRBORNE AND COMPASS INFO WAS LOST; THE FLT CREW ELECTED TO RETURN. THE REPORTER STATED THAT IN THE FUTURE; A REALIGNMENT WILL BE ATTEMPTED BEFORE TAKING THE RWY. THE SOURCE OF THE ACRID ODOR IN THE CABIN COULD NOT BE LOCATED OR IDENTIFIED AND REMAINS A MYSTERY.