| 摘要 |
<p>Part of a printed circuit board circuit is made up of three gates (30, 31, 32) each of which are formed on a different device and interconnected by means of the board print so that connections (35, 36) may be established by means of probes. Associated with the inputs and outputs of each device are phantom diodes (such as diode 32) which are normally connected to circuit ground (38) but which in the case of one gate (31) are connected the supply rail (37), the device of which it forms part having been mounted in the board in the wrong orientation. By the steps of connecting one device power input pin to a test ground potential (38), raising the potential of the other power input pin via connection to a supply rail (37) and lowering the potential of an active pin (33) a diode (302) may be made to conduct current via path (304) indicating that the device (31) is wrongly orientated. The applied low potential is insufficient to bring correctly connected diodes (such as that of device 30) into conduction.</p> |
