The circuit given below fails to produce data output. The individual flip-flops are checked with a logic probe and pulser, and each checks OK. What could be causing the problem?

• The data output line may be grounded.
• One of the clock input lines may be open.
• One of the interconnect lines between two stages may have a solder bridge to ground.
• One of the flip-flops may have a solder bridge between its input and Vcc.