What action is necessary to check the functioning of a SCR using an ohmmeter?

To check the functioning of a Silicon Controlled Rectifier (SCR) using an ohmmeter, shorting the gate and anode is essential. This action allows for testing the SCR’s ability to switch on and off properly. When the gate terminal is shorted to the anode, it provides the necessary gate trigger voltage that can turn the SCR on, allowing current to flow between the anode and cathode. An ohmmeter can then measure the resistance in this scenario, verifying that the SCR is operational and can conduct as expected when triggered.

The other options do not appropriately facilitate the testing of an SCR with an ohmmeter. For instance, connecting all terminals together could potentially lead to inaccurate readings or damage, using high voltage is not safe for this type of test, and measuring the current directly is not feasible with a standard ohmmeter, as it is not designed to measure current flow but rather resistance. Therefore, shorting the gate and anode is the correct method for testing the SCR's functionality with an ohmmeter.