* Sharp slumps 28 pct, lowest close since 1976 * Sony sags 7 pct, lowest finish since 1980 * Fast Retailing up as July same-store sales beat expectations TOKYO, Aug 3 (Reuters) - Japan's Nikkei average fell on Friday after the ECB disappointed investors by offering no immediate action to prop up the euro, with wide quarterly losses from Sharp and Sony adding to the gloom.