Abstract: A printed circuit board to be tested on a test fixture mounts sealingly on a movable top plate having through holes located directly beneath test points on the board. A base plate below the top plate is provided with a plurality of upstanding, spring-loaded test probes arranged to pass through the holes in the top plate when the two plates are drawn together by a vacuum established in the space between the plates. A resilient gasket seals the perimeter of the plates defining the vacuum chamber between the plates. The plates are held resiliently apart by compression springs. A vacuum source is connected to the vacuum chamber by a vacuum control. The test probes are of two different heights. When a full vacuum is applied to the vacuum chamber, the plates are pulled close together and all test probes contact test points on the circuit board in a first test mode of operation.