IBM PCjr Hardware Maintenance And Service page 276

13. Remove the four system board mounting screws
14. Remove the system board mounting screw 0, if
present.
15. Use your finger to apply pressure to the hold-down
latches 0 and lift the system board enough to
clear the latches.
Note: The system board is held by two
hold-down latches on the left side and a
mounting slot on the right.
System Unit 4-100-7