First you can check some voltages to find any difference between the working and non working EDU08.
You can test the voltages on SK1 connector on the top board.
(It is connected to the pin header SK7 on the bottom board.)
You can use the input ground lead as GND reference.
The voltages on the pins should be:
Top row from left to right 3.3, 0, 0, 0, 0, 0, 3.3, 0, 0.4
Bottom row 0, 3.3, 0, 0, 0, 0, 0, 3.3, 0
You can also check the voltages on the points marked A…M in this picture:
Check if there is any difference between the working and not working units.
In this thread there is info about the display: