What was found
FO MA ON BOTH FD LOST AT LIFT OFF. CAME BACK ON AFTER SELECTIN G HDG SEL AND VNAV ABOVE 400FT. TECH SUPPORT. TAT PROBE, RT ADIRU AND RT FCC REPLACED=NO HELP REF FIM 22-11-D16. PULL UP SSM 22-11-14-101. ACCESS DFCS BITE " DISCREET INPUTS THROUGH THE CDU REF AMM 22-11-00-740-801.GO TO "J1A" WHICH IS THE FCC BENCH PLUG "A" CONNECTOR AND LOOK AT PIN "F4". CYCLE THE CAPT AND THEN THE F/O SIDE TO/GA SWITCHES ONE AT A TIME AND WATH FOR THE STATUS.CHANGE.SUSPECT F/O TO/GA SWITCH. AS PER TECH SUPPORT RECOMMENDATION, R/R FO TAKEOFF/GO-AROUND SWITCH REF. AMM 22-11-39. OPS CHECK GOOD. UNABLE TO DUPLICATE ORIGINAL FAULT.