What was found
IN FLIGHT MIA-SDQ, BOTH CAPTAIN AND FIRST OFFICER LOWER SCREEN DISPLAYED "MAP" AND LOST NAVIGATION INFORMATION. ALSO, L SA FAIL. LOST LEFT SIDE, BOTH SCREENS. AN IN-FLIGHT EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO MIA. UPON LANDING MAINTENANCE PERSONNEL REMOVED AND REPLACED BOTH CAPTAIN AND FIRST OFFICER FMC I/A/W B767 AMM 34-61-01. OPS CHECK ON BOTH WAS GOOD. ALSO, RESET THE EFIS SYMBOL GENERATOR I/A/W B767 AMM 34-22-01. PERFORMED AN EFIS TEST, NO DEFECTS NOTED, OPS CHECK GOOD. PART INFORMATION FOR CAPTAIN'S FMC NOTED BELOW IN SECTION 5. FIRST OFFICER FMC PART INFORMATION AS FOLLOWS: FMC P/N 4052506-955, S/N 31251677. PART DISPLAYED FAULTY INFORMATION IN FLIGHT.