Yesterday I checked the voltages with my DMV and everything looked OK. Today I checked with the ‘scope just to check for ripple and they all look pretty clean to me.

Clocks

I also saw that there was a running clock but overnight I became increasing worried that it wasn’t a very good clock.

Here’s the circuit…

It doesn’t look too tricky.

Check with the scope.

A scope trace shows it’s a bit funny. I’m not sure quite what the Z80 needs but I thought it should have a better back edge than that.

More thought needed.