Fabio Battaglia blogged about his Ithaca Audio Z80 CPU card for the S100 bus project:
First of all, I assembled some simple test code to write a letter on my video console, just to check that code was actually executing. Obviously I only got a black screen at first, which seems a constant when I build these cards. I ended up tracing the problem on pin 53 of the bus: on the IEEE696 standard (the last, and official, iteration of the bus) that pin is always grounded, on the Ithaca card the pin is used to enable/disable internal buffer to allow manual data input on the processor lines. Once found, it was a matter of disconnecting a two IC legs and a little rewiring.
Pull out pin 2 of IC14 and tie it to 5v, then pull out pin 12 of IC16. That’s it. And then, the board started to show signs of life!