Abstract: For in-circuit and functional testing of loaded printed circuit boards with speed and precision, a vacuum-actuated test fixture utilizes a yielding diaphragm assembly with rigid frame and spring-loaded diaphragm base plate, to distribute downward atmospheric pressure evenly over the entire area of the board without localized stress concentrations. A captive removable diaphragm frame and quick-acting spring-loaded cam latches assure a positive seal around the margin of the diaphragm assembly and along top and bottom edge portions thereof. Ease of assembly and disassembly is promoted. A plug-in vacuum adapter with manual valve provides quick hook-up of the test fixture to a vacuum source. A lower base frame and patchboard assembly allow efficient interfacing of the text fixture with a suitable receiver frame of test apparatus.