Abstract: An in-circuit test apparatus having a vacuum chamber between a top plate and a base plate. The apparatus has an adjustable bearing block assembly located at each quandrant to provide a precision alignment between the top plate and the base plate. A continuous double-hollow tube is located in a uniform groove in the base plate and forms a seal when held captive between the top plate and the base plate. A plurality of spring probe pressure pins are mounted within the chamber. The pins project through drilled individual access ports in the top plate and make electrical contact with a printed circuit board under test when the top plate collapses under a vacuum.