I built one in part from scratch.
Well at least the control panel and CPU board. That included laying out and etching the circuit cards and soldering on chip sockets. The CPU board had Z-80 processor and the EPROM with a "borrowed" 4 KB BASIC interpreter and what is in effect a BIOS. As I recall, besides the S-100 board which has nothing but connectors, I bought an 8 KB memory card and a display card which attached to a TV.
The control board had umpteen switches for setting up addresses and loading data into memory. It was possible to step through one CPU instruction at a time. Also, I had circuitry to write and read data to an audio tape recorder.
Biggest problem was it was extremely noisy RF wise. You could not watch a TV anywhere in the house.
I bought a TR-80 and retired the S-100. But, I even modified the TRS-80 so it could display lower case characters.
The control board had umpteen switches for setting up addresses and loading data into memory. It was possible to step through one CPU instruction at a time. Also, I had circuitry to write and read data to an audio tape recorder.
Biggest problem was it was extremely noisy RF wise. You could not watch a TV anywhere in the house.
I bought a TR-80 and retired the S-100. But, I even modified the TRS-80 so it could display lower case characters.