What was found
BUS DC R OFF BUS AC R OFF LOST DU 4, 5, 6 & NR 2 MCDU. PERFORMED FIM 24-30 TASK 805 & FOUND RPCDU GCU FAULT. REMOVED AND REPLACED RPCDU PER 717 AMM 24-21-04 & REMOVED AND REPLACED POWER RELAYS PER 717 AMM 24-21-06. RPCDU OPS CHECKS GOOD PER 717 AMM 24-21-04. OK FOR CONTINUED SERVICE.