In-circuit Test Probe Pogo Pin PE50 for PCBA Inspection In-circuit test probes are mainly used for testing electrical performance of in-circuit components on PCB and the connection between circuit networks. It could quantitatively measure components such as resistors, capacitors, inductors, crystal oscillators, and perform functional tests of diodes, triodes, optocouplers, transformers, relays, operational amplifiers, power supply modules and integrated circuits.