TTL fault diagnosis: An inverter (NOT gate) has an internal open circuit. What DC level would you most likely measure directly at the inverter’s output pin in such a fault condition?

Introduction / Context:
Diagnosing TTL faults often involves recognizing characteristic voltages. A healthy TTL LOW is typically below about 0.4 V, and a healthy TTL HIGH is typically above about 2.4 V. Faults can yield mid-levels near 1.6 V, which are indeterminate for logic.

Given Data / Assumptions:

• Standard TTL inverter with a totem-pole output stage.
• Internal open circuit disrupts the normal pull-up/pull-down path.
• No external pull resistors clamping the node.

Concept / Approach:
With an internal open, the output transistor network cannot drive a valid HIGH or LOW. The node may sit at a mid-rail potential due to leakage and internal bias, commonly around 1.6 V in TTL, which is outside guaranteed logic thresholds and thus undefined for reliable operation.

Step-by-Step Solution:
1) Identify normal TTL VOH >= ~2.4 V, VOL <= ~0.4 V.2) An internal open removes a solid current path, leaving the node to float to a mid-level.3) The common observed mid-level is near 1.6 V.

Verification / Alternative check:
Service manuals and TTL family datasheets discuss undefined mid-levels under fault conditions; scope measurements typically show unstable or mid-rail DC.

Why Other Options Are Wrong:
“Less than 0.4 V” and “Greater than 2.4 V” imply a healthy LOW or HIGH; “All of the above” cannot be correct because these are mutually exclusive ranges.

Common Pitfalls:
Assuming every failure rails the output; confusing TTL thresholds with CMOS levels.

Final Answer:
1.6 V