Abstract: A circuit board test fixture has a mount with slots for loosely receiving the marginal edges of a diaphragm. Sealing surfaces curve downwardly from the slots for the diaphragm to form a direct seal against when drawn tightly thereabout. Innermost faces of the mount are spaced outwardly from the marginal edges of a backing plate that supports the diaphragm and moves perpendicular thereto. The mount projects upwards from a vacuum chamber base that is hingedly connected to a connector housing. The mount will maintain a seal with the diaphragm for an operative vacuum chamber when the base is pivoted upwardly to almost an upright position.