What possible reasons that the output of a particular inverter is stuck LOW while its input is pulsing?
What possible reasons that the inverter output is stuck at an indeterminate logic level?

 

Hint for first question:

Back in the early 80's, ET2 Poole and I were sent out to the flight-line at Barber's Point NAS to determine why the automated weather recording station was not reporting in to the tower. Using the six-step troubleshooting method, we quickly determined the fault was due to the charred remains of a gekko that had unwisely chosen to rest atop the power input terminals.

Hint for the second question:

What is the voltage level across an unconnected TTL input?

 

I dun understand it. i just want to learn...