NEIEP Mechanics Practice Exam

To check a silicon controlled rectifier (SCR) for proper triggering operation with an ohmmeter, it's essential to establish the correct firing condition. Connecting a jumper from the gate to the anode simulates the triggering signal necessary for the SCR to turn on. This action allows the device to conduct when the gate receives a positive voltage relative to the cathode.

Once the jumper is removed, the SCR should remain in the conducting state if it has been triggered correctly. Testing after removing the jumper verifies whether the SCR is functioning and capable of holding a conduction state. This testing method is critical because it ensures that the SCR responds appropriately to gate signals, an essential function for devices operating in power electronics.

Other options may not effectively ensure the SCR's proper functioning. Connecting the positive lead to the cathode primarily checks for internal shorts but does not assess triggering. Using alternating current for testing is not suitable for this purpose since triggering requires specific voltage conditions that are best understood with direct current measurements. Disconnecting all leads before testing would prevent any meaningful analysis, as there would be no connections to test the SCR's behavior.