Abstract: A top-accessible system for simultaneously testing both sides of a printed circuit board includes a vertically movable top plate, upon which the circuit board may be rested, and a framed bottom plate which underlies the top plate and defines a vacuum chamber therewith. A mounting plate is pivoted to the upper side of the top plate for movement to a latched test position over the circuit board. A probe plate is movably carried by and is parallel to the underside of the mounting plate. With the mounting plate in its test position a cam structure thereon is operated to drive the probe plate transversely toward the circuit board to cause upper test pins on the probe plate to perpendicularly contact test points on the upper side of the circuit board, and cause hold-down members on the probe plate to contact the circuit board and firmly hold it against the top plate.