The other black box, a data recorder that had also been retrieved from the bottom of the Mediterranean after the aircraft plunged into the sea, has already been accessed.
It had confirmed that smoke alarms had sounded in the Airbus A320 before it went down on May 19th, while flying from Paris to Cairo with 66 people on board.
"None of the memory chips of the electronic board was damaged," the Egyptian-led probe said in a statement.
Other circuitry had to be replaced, however.
"After the replacement of the... board components, test results were satisfactory and it enabled the reading of the recorders," the statement said.
Investigators said last week that the plane's wreckage showed signs of fire while the data recorder confirmed smoke alarms had been activated.
They had previously announced that the plane's automated Aircraft Communications Addressing and Reporting System (ACARS) sent signals indicating smoke alarms on board the plane before it went down.
The plane was carrying 40 Egyptians, 15 French, two Iraqis, two Canadians and one passenger each from Algeria, Belgium, Britain, Chad, Portugal, Saudi Arabia and Sudan.