In-circuit testing (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" test fixture and specialist test equipment, or with a fixtureless in-circuit test setup. Fixtures for in-circuit testing A common form of in-circuit testing uses a bed-of-nails tester. This is a fixture that uses an array of spring-loaded pins known as "pogo pins". When a printed circuit board is aligned with and pressed down onto the bed-of-nails tester, the pins make electrical contact with locations on the circuit board, allowing them to be used as test points for in-circuit testing. Bed-of-nails testers have the advantage that many tests may be performed at a time, but have the disadvantage of placing substantial strain on the PCB. An alternative is the use of flying probes, which place less mechanical strain on the boards being tested. Their advantages and disadvantages are the opposite of bed-of-nails testers: the flying probes must be moved between tests, but they place much less strain on the PCB. Example test sequence Discharging capacitors and especially electrolytic capacitors (for safety and measurement stability, this test sequence must be done first before testing any other items) Contact Test (To verify the test system is connected to the Unit Under Test (UUT) Shorts testing (Test for solder shorts and opens) Analog tests (Test all analog components for placement and correct value) Test for defective open pins on devices Test for capacitor orientation defects Power up UUT Powered analog (Test for correct operation of analog components such as regulators and opamps) Powered digital (Test the operation of digital components and Boundary scan devices) JTAG boundary-scan tests Flash Memory, EEPROM, and other device programming Discharging capacitors as UUT is powered down While in-circuit testers are typically limited to testing the above devices, it is possible to add additional hardware to the test fixture to allow different solutions to be implemented. Such additional hardware includes: Cameras to test for presence and correct orientation of components Photodetectors to test for LED color and intensity External timer counter modules to test very high frequencies (over 50 MHz) crystals and oscillators Signal waveform analysis, e.g. slew rate measurement, envelope curve etc. External equipment can be used for hi-voltage measurement