The assembled circuit board is first visually inspected for any shorts/opens in the circuit. The circuit is then tested using an Ohmmeter. This is to ensure that power supplies, inputs and outputs are not shorted to ground or to each other. This is an important step before powering up the circuit and avoids costly damages to circuit components.
The circuit power supplies are checked after powering up and circuit is checked for its intended function using multimeter and/or oscilloscope. It is a good practice to provide test points/probes for power supplies, inputs, outputs and critical circuit nodes. The circuit is tested in a stepwise manner isolating it from output stages where possible. Never test circuit impedance's while circuit is powered up. To test circuit node impedance, isolate it from other nodes. Consider loading effects while testing the circuit using multimeter/oscilloscope. For example, measuring voltage across 1 MOhm resistor with a multimeter having 10 MOhm input impedance will drop the voltage by approx. 10 while measuring AC voltages. Most multimeter AC ranges are calibrated to RMS of sine and are grossly inaccurate in measurement of non-sine signals such as square wave. True RMS AC voltage function is required to accurately measure non-sine signals.
Use single point grounding to avoid grounding errors in low voltage measurement. Also, use neat compact layout and short wire lengths in high frequency AC circuits.
Use appropriate test prods to check circuit voltages and avoid damages due to short circuits in powered circuits. Take extra precaution while checking voltage onto IC pin. Switch off power to the circuit while replacing an IC or a component or while doing solder rework on PCB.
ANU Engineering - ENGN2211