It turns out you can have a lot of fun failing to get something to work. Number one son has bought an RC2014 homebrew Z80 kit. At the moment it is not doing much, so we had a go at finding out what the problem might be. The kit has a backplane board that brings out all the signals from the processor and then you can plug in a processor board, clock, RAM board, ROM board and serial port. It really took me back to the days when you could print out the entire circuit for your computer on a single sheet of paper.
If you really want to discover how a computer works you could do a lot worse than get one of these. Although in our case what we discovered was that it doesn't work just at the moment.
Fixing problems like these is always a matter of working through each part of the system, checking it and moving on. By the end of our session we'd proved that the serial data was getting from our terminal into the UART, the processor clock was running and the Z80 was trying to load things from the bus. It still wasn't working, but we had a great time anyway.