Abstract: A rack for supporting a plurality of burn-in boards and thermal boards which carry heat sinks to be associated with circuit chips mounted on the burn-in boards, has a first side frames that support the burn-in boards in a fixed position. Movable frames adjacent each of the side frame have a plurality of supports for thermal boards which include heat sinks, temperature sensors and other components. The movable frames are slidably mountable in a direction perpendicular to the burn-in board. Cams control the movement of the movable frames so that the thermal boards and components carried thereby can be moved from a position clearing the burn-in boards to permit insertion of the burn-in boards, onto the rack to a position wherein the components contact chips on the burn-in boards for good thermal control of the circuits on the burn-in boards.