A system for testing for opens in and shorts between conductor traces on a printed circuit board includes an electron gun assembly for generating an electron beam and an electron optics assembly for directing the beam to the traces which have a reference potential. A grid located proximate to and substantially parallel with the surface of the board is placed at a first potential before the beam is directed to a first point on a trace to charge the trace to a first potential. The grid is then placed at a second potential, the second potential being between the reference potential and the first potential, before the beam is directed to a second point on the trace to cause emission of secondary electrons. The secondary electrons that reach the grid are collected thereby, and signal processing electronics are used to determine whether or not an open or short exists.