Please see the screen shot of the 74LS161 wave form. the yellow line is the clock input. the blue line is the QA counter output. I am surprised to see such a large negative voltage spike of the counter output. The negative spike last about 80ns.
My question is that: is it normal?
btw, nothing is connected to the counter, just one 74LS161 on the breadboard, input clock, enable T,P, disable load, disable clear, and measure the output. I added a 0.1uF despike cap, doesn't help on the output spike.