Special thanks to PCBWay for sponsoring this video. https://www.pcbway.com/ Today I have a rubber key 48K ZX Spectrum issue 3B on the bench. This particular motherboard is an unusual dark green color, manufactured in Korea, and it arrived with a completely dead data bus. Using a diagnostic card and an oscilloscope, I trace the power, clock, and reset signals to figure out why the system refuses to boot. After ruling out the ULA, the focus shifts to the Z80 CPU. I remove the original processor, test a replacement, and install it to see if that resolves the erratic data lines. Once the repair is done and the display is stabilized with a composite mod, I test the system with a quick run of Manic Miner. ───────────────────────────── If you'd like to help keep the lights on (and the tools plugged in), my Patreon is the best way to do it. Patrons get ad-free early access to videos, behind-the-scenes updates, and entry to a super secret Discord channel — plus my sincere gratitude, which is worth roughly what you'd expect. ▸ Patreon: https://www.patreon.com/c/morefunmakingit ───────────────────────────── I also have another channel called More Fun Making It, where I build things from scratch instead of trying to coax life back into them. Same shed, different end of the workbench. ▸ More Fun Making It: https://www.youtube.com/@MoreFunMakingIt ───────────────────────────── There's also the Retro Hardware Discord, where people who enjoy this sort of thing gather to talk about it. It's better than it has any right to be. ▸ Retro Hardware Discord: https://discord.gg/ChH726tbbF ───────────────────────────── #ZXSpectrum #RetroComputing #Z80