This invention relates to a cartridge assembly tray for conducting automated biochemical tests, such as immunoassay tests. The tray comprises a base member, a hinged frame and a locking mechanism. The base member includes a plurality of slots within the base member. Each of the plurality of slots is to receive a test cartridge. The hinged frame is coupled to the base member. The hinged frame is capable to rotate to an opened position or a closed position. The hinged frame includes a horizontal push bar configured to apply a downward force to test cartridges received in the plurality of slots when the hinged frame is in the closed position. The locking mechanism is to lock the hinged frame in the closed position when the hinged frame rotates to the closed position.