I’m making the circuit for this project using things I have in my parts box - a lot of the parts are salvaged from computer systems dating back to the 1980s and 1990s. The Z80 is a Mostek part manufactured in 1983 and last used in 1995. I made a 4MHz clock circuit using a 74LS04 as per the series resonant schematic on this page.

I pulled all Z80 inputs to 5V using 47k resistors, and pulled the data bus to 0V so that the Z80 executes NOP instructions.

I’m using a Velleman HPS140i to check that the Z80 appears to be operating. Connecting the scope probe to address bit A11 shows the expected 1KHz square wave.