Building a CPU Tester for Z80 CPUs

In this video, I build a dedicated Z80 CPU tester to help diagnose failed processors found during recent ZX81 and Spectrum repairs. This project focuses on identifying original NMOS versus later CMOS variants, which differ in power consumption, heat production, and undocumented behaviour. The build uses a red PCB from PCBWay and includes an SMD resistor modification to fit a specific footprint. After assembly, I test various Z80s from my parts bins, identifying several dead chips and units with simple bent pins. Important Note on the Current Jumper: The current jumper must be installed by default for the tester to function. While the instructions suggest removing it to measure current with a multimeter, the device will not run or show test activity without the jumper in place. Tester Limitations: This tool primarily exercises address lines using a small test program. Some complex faults, such as issues with the HALT line or other specific inputs/outputs, still require advanced diagnostic tools like the Backbit Chip Tester Pro