"None of the memory chips of the electronic board was damaged," the Egyptian-led probe said in a statement.
That means that recordings of what went on in the cockpit can be heard, which is likely to give clues as to the reason the Airbus A320 suddenly disappeared from radar screens between the Greek island of Crete and the Egyptian coast on 19 May.
The flight recorder is currently being repaired by France's BEA air traffic accident investigation unit.
Analysis of the other black box, the flight data recorder, has confirmed that smoke alarms went off before the crash, indicating that the probable cause was technical failure and not a terrorist attack, as Egyptian authorities originally speculated.
Last week investigators said that the debris showed signs of a fire inside the aircraft.
There were 66 people on board - 40 Egyptians, 10 of whom were members of the flight crew, and 15 French nationals.