I think this barely qualifies as a home computer but it was at the front of the queue to be repaired or, at the very least, looked into. This is an S-100 board, fitted with an 8080 processor and some very simple front panel and display. It was designed by George Morrow, who would move on to design a number of Z80 CP/M (MD-1) and 808x computers through Morrow Designs. Again, I guess calling this one a home computer would be a stretch, but anyways. It is also not operational, for reasons yet unknown.
The 8080 is a weird processor when compared to other 8 bit CPUs, it requires three different voltages (+5V, +12V and -5V) and two different clocks (phi1, phi2). It is typically paired with an 8224 clock generator which, besides the two clock signals, also provides or forwards a number of useful signals (RESET, etc). I have tried to narrow down the potential issues by testing the logic chips with my EPROM programmer, and using a poor man NOP generator (bringing data lines to GND through a small resistor at the CPU). Voltages are okay, clocks and most other important signals also look okay, and I can also reset the CPU just fine, but there is something wrong going on with the address lines. I have barely started with the process during the weekend so there is still some ground to cover.
Borked display upon startup.
Poor man NOP generator trying to do its thing.
Poor man scope peeking at clock signals.
The 8080 is a weird processor when compared to other 8 bit CPUs, it requires three different voltages (+5V, +12V and -5V) and two different clocks (phi1, phi2). It is typically paired with an 8224 clock generator which, besides the two clock signals, also provides or forwards a number of useful signals (RESET, etc). I have tried to narrow down the potential issues by testing the logic chips with my EPROM programmer, and using a poor man NOP generator (bringing data lines to GND through a small resistor at the CPU). Voltages are okay, clocks and most other important signals also look okay, and I can also reset the CPU just fine, but there is something wrong going on with the address lines. I have barely started with the process during the weekend so there is still some ground to cover.
Borked display upon startup.
Poor man NOP generator trying to do its thing.
Poor man scope peeking at clock signals.
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