When checking a known-good SCR or TRIAC with an ohmmeter (no gate drive applied), what resistance behavior should be observed between the main terminals?

Introduction / Context:Basic ohmmeter checks can reveal gross faults in thyristors. An SCR or a TRIAC that is not triggered should block current. Recognizing the expected high resistance reading prevents misdiagnosis and helps identify shorted devices.

Given Data / Assumptions:

• No gate current is applied during the test.
• Meter polarity is reversed to check both directions.
• Device is not damaged and has no internal leakage beyond normal levels.

Concept / Approach:Without gate drive and below breakover voltage, an SCR (anode–cathode path) and a TRIAC (MT1–MT2 path) should be non-conductive. Therefore the ohmmeter—especially a DMM with low test voltage—will show a very high resistance (open) in either polarity for a healthy device.

Step-by-Step Solution:Connect ohmmeter leads across main terminals (A–K for SCR, MT1–MT2 for TRIAC).Measure resistance with one polarity: observe very high resistance.Reverse the leads: again observe very high resistance.Conclusion: High resistance in both directions indicates a good, untriggered device.

Verification / Alternative check:Applying a small gate current will cause the SCR/TRIAC to conduct (low resistance). Removing gate drive and reducing current below the holding current returns the device to high-resistance state, confirming correct operation.

Why Other Options Are Wrong:

• b) and c): Suggest diode-like conduction in one direction; an SCR/TRIAC needs triggering.
• d): Low resistance both ways indicates a shorted device.
• e): No fixed midrange resistance is expected for an untriggered thyristor.

Common Pitfalls:

• Using an old analog ohmmeter with high test voltage can accidentally trigger the device—use caution.
• For TRIACs, mistaken terminal identification can lead to confusing readings.

Final Answer:show high resistance in both directions