What was found
WHILE EN ROUTE FROM MEM TO AEX, THE F/O'S EHS 1 WENT BLACK. RAN THE QRH AND FOUND THE COMPOSITE MODE TO WORK NORMAL ON F/O'S EADI. AFTER TALKING WITH DISPATCH VIA RADIO, DIVERTED THE FLIGHT BACK TO MEM. REMOVED AND REPLACED F/O'S ELECTRONIC FLIGHT DISPLAY (LOWER) IAW AMM 34-24-15. OPS CHECK GOOD IAW AMM 34-24-00, P/N OFF/ON 622-6342-022, S/N ON 5171, S/N OFF 5302. ALSO, REMOVED AND REPLACED DPU IAW AMM 34-24-20. OPS CHECK GOOD IAM AMM 34-24-00, P/N OFF/ON 622-7713-004, S/N ON 6720.