This is a ZX Spectrum 48K, issue 6A, from ZXevious. He asked me for advice on how to repair its speccy. Came with a faulty Interface 1, which I speak about in another article.

Upon switching on, the screen shows flashing blocks, hangs, and the screen data is mixed with something that seems digital noise. Maybe from poorly coupled data lines.

ULA is operational, Z80 too, so the main candidate is low memory. First thing is to try to isolate which memory chip (or chips) are damaged. The usual cartridge ROM tests I ran didn't give a clue, as it seemed that every chip was damaged. Strange enough that all power lines were ok.