JK flip-flop chain troubleshooting (clocking issue) A sequential circuit shows no output activity at Q1 when observed on an oscilloscope. Conditions: all J–K inputs are held HIGH, the system CLK signal is present, Q0 is toggling, and the C (clock) input of flip-flop FF1 is stuck at a constant LOW. What is the most likely cause of this problem?

Introduction / Context:
This question tests practical debugging of ripple or chained JK flip-flops. With J = K = 1, each JK device toggles on its clock edge. If the next stage's clock pin never sees transitions, that stage cannot toggle. Recognizing whether the issue is at the driving node (previous flip-flop output) or at the receiving node (next flip-flop clock input) is essential for rapid fault isolation.

Given Data / Assumptions:

• All J–K inputs HIGH → each stage is configured to toggle on its clock.
• Global CLK present; Q0 is toggling, so FF0 is healthy internally.
• FF1's C (clock) input is observed constant LOW.
• Standard wiring: Q0 often drives the clock of FF1 in ripple chains.

Concept / Approach:
For FF1 to toggle, its clock input must receive transitions. If its clock node is stuck LOW while Q0 is known to toggle, there is likely a fault between Q0 and FF1.C. The two most probable hard faults are a short-to-ground at the driving node (FF0.Q0) or at the receiving node (FF1.C), either of which will clamp the signal line LOW and prevent edges from reaching FF1.

Step-by-Step Solution:

Verification / Alternative check:
An ohmmeter (with power off) often reveals a near-0 Ω path to ground on the affected node. Visual inspection for solder bridges or damaged vias also helps. Replacing the offending IC or repairing the short restores clock edges at FF1.C and Q1 toggling returns.

Why Other Options Are Wrong:

• The Q0 to J connection (A): J controls toggle when J=K=1; the immediate symptom is a missing clock at FF1, not a data-path issue.
• Only FF0 output shorted (B) or only FF1 input shorted (C): Each is possible, but the best answer acknowledges either end of the same net could be shorted.

Common Pitfalls:
Assuming a logic design error when the probe already shows a hardware-level short; overlooking that a stuck clock pin will prevent any downstream activity even with correct J–K settings.

Final Answer:
Either the output of FF0 or the input of FF1 may be shorted to ground.