Measurement techniques (6):

If a circuit ceases to function and it shows no visible damage, a voltage analysis should be the first step in locating the fault. Voltages can normally be measured without the need of breaking connections or the removal of components. The level and polarity ofa voltage are two aspects that indicate the state of a cornponent or cireuit. Because of that, many circuit and wiring diagrams give the voltage level and polarity at important junctions. Such indicationsare agreat help in faultfinding, but even without them, the voltage at many points in a circuit is known. For instance, the potential across a p-n junction of a diode or the base-emitter junction of a transistor should be O.2-0.4 V (germanium) or 0.6-0.8 V (silicon).