How will the new SD81Booster be for ZX80 and ZX81
SD81Booster expands ZX80 and ZX81 with microSD, 512 KB of paged RAM, AY sound, and expanded graphics without losing compatibility with the original machine.
Tutorial repair ZX Spectrum 48K by Manuel Cuenca. First steps to repair your ZX Spectrum. First and second part
First steps to diagnose your ZX Spectrum 48K with Manuel Cuenca: power supply, connection, types of board, and voltage measurement in two installments.