In-circuit test Limitations Printed circuit
In-circuit test (ICT) is an example of white box testing where an electrical probe tests a populated printed circuit board (PCB), checking for shorts, opens, resistance, capacitance, and other basic quantities which will show whether the assembly was correctly fabricated. It may be performed with a bed of nails type test fixture and specialist test equipment, or with a fixtureless in-circuit test setup.
While in-circuit test is a very powerful tool for testing PCBs, it has these limitations:
Parallel components can often only be tested as one component if the components are of the same type (i.e. two resistors);though different components in parallel may be testable using a sequence of different tests - e.g. a DC voltage measurement versus a measurement of AC injection current at a node.
Electrolytic components can be tested for polarity only in specific configurations (e.g. if not parallel connected to power rails) or with a specific sensor
The quality of electrical contacts can not be tested unless extra test points and/or a dedicated extra cable harness are provided.
It is only as good as the design of the PCB. If no test access has been provided by the PCB designer then some tests will not be possible. See Design For Test guidelines.