What was found
AIR TURN BACK, AFTER LIFT OFF CAPT AND F/O PRIMARY DISPLAY AND NAV DISPLAY WENT BLANK, AIRSPEED INDICATOR, ALTIMETER SHOWED FLAGS. GONE AHRS DISPLAYED. CAPT`S VSI AND CAPT`S RMI SHOW HDG FLAG AND VSI AND RA FLAGS. FTR AND RTS WERE ACCOMPLISHED AT BOTH DFGC SHOWED GO IAW AMM 22-01-05, PAG 204. OPERATIONAL TEST ADC AMM: 34-16-01 PAG 02 ITEM 7 AND ACCORDING AMM: 34-21-10 PAG 201. BOTH ATTITUDE AND HEADING REFERENCE UNIT WERE REPLACED, TEST SATISFACTORY IAW AMM 34-14-01 VSI OPERATIONAL TEST WAS ACCOMPLISHED AND AMM 22-01-05 DFGS TEST ACCOMPLISHED WERE FOUND SATISFACTORY. (K)