Problem with testing 74ls173AN D flip-flop
A number of tips about dealing with (LS)TTL:

1) Inputs should be either grounded or pulled high with a 1k pullup resistor.

2) Output LEDs should be connected to +5 with a 1k pullup resistor. And yes, this will produce a signal inversion in the sense that a LOW output will turn on the LED.







simulate this circuit &ndash; Schematic created using CircuitLab

3) You must decouple the power pin. Connect a 0.1 uF ceramic cap from pin 16 to pin 8, and don't use jumpers - plug the leads directly into the breadboard at the IC.

Make sure you test the LED polarity by unplugging the IC, applying power, and grounding the output contact. If the LED doesn't light up, it's bad or you've got it backwards. When you've checked out the LEDs, turn off power and plug in the IC.

Otherwise your circuit looks OK with one exception. You've missed the part in the Youtube video where it is pointed out that TTL inputs float high if no connection is made, so your circuit really ought to be turning on ALL the LEDs, not just the 2 that are connected to +5. With proper LED connections, leaving the inputs floating or pulled high should result in all LEDs being off.

Finally, using a switch to generate a clock to a flip-flop is fine for what you're doing now, but anything more complicated will require debouncing of the switch.