a component failure diagnostic circuitry detects the address of the faulty component and places the address on the system address bus the diagnostic circuitry controls each array to forward the output signal from the selection circuit on the associated printed circuit board to a register which has a position associated with each printed circuit board since only the selection circuit in the array which contains the faulty component responds to the address of the faulty component the diagnostic register can be examined by the diagnostic circuitry to detect the position of the faulty board application_number US 14959588 A description fig1 is a schematic diagram of a portion of a computer system in which various system components are physically mounted on separate printed wiring boards in such a system the printed wiring boards typically plug into a backplane 108 which is a large electrical chassis or back plate on which are mounted a plurality of conventional printed circuit board 34 edge 34 connectors each of which comprises a 34 slot 34 for a printed circuit board these connectors are electrically wired to power and ground and may also be connected together by means of multiple wire paths which form a computer bus one or more printed circuit wiring boards which comprise the main.