Probe apparatus for in place testing of electrical circuit boards

Probe apparatus is disclosed for in place testing of circuit boards of the type which carry electrical components interconnected at nodes accessible from at least a first side of the board. The probe apparatus may comprise a card which is attached to the circuit board under test adjacent its first side. A probe module, including signal conditioning means and a short interfacing element, is mounted on the card in close proximity to the node of interest. The signal conditioning means and interfacing element may comprise electrical decoupling and signal pick off means capable of sensing signals at the node while minimizing introduction of spurious signals thereto.