Abstract: A test fixture for testing a circuit board, comprising a top plate defining a board-bearing surface for receiving the circuit board to be tested thereon. The test fixture comprises a lid having a lid frame defining a peripheral rim, and a lid diaphragm movably mounted to the frame opposite the peripheral rim; the lid diaphragm defines an inner surface to which is mounted a circuit board securing member. The lid is movable between a first position where the frame rim engages the top plate to define a test chamber about the board-bearing surface and between the top plate, the frame and the diaphragm, and a second position where the lid is moved away from the top plate to allow access to the test chamber.