A: The low 16K of RAM is damaged. The Spectrum uses that for screen memory and system variables. You must replace the lower RAM chips (usually 4116 or 4416) before any software will run.
Comprehensive RAM soak tests, ULA timing, keyboard matrix, and ROM checksums. 2. Retroleum SMART Card Diagnostics
It provides a very clear visual map of the 4116 and 4532 RAM chips, showing you exactly which physical chip on the board needs to be desoldered. zx spectrum test program link
This guide explores the best diagnostic software available, how to deploy them, and where to find the essential download links to revive your classic hardware. Why You Need a ZX Spectrum Test Program
Available via GitHub. Search for "Brendan Alford zx-spectrum-diagnostics link" to find the latest compiled .rom files. Retroleum SMART Card Diagnostics A: The low 16K of RAM is damaged
Unlike modern computers, the ZX Spectrum does not have a built-in Power-On Self-Test (POST) that explains what is wrong. If a RAM chip fails or the Uncommitted Logic Array (ULA) overheats, the computer might simply freeze.
To use these files, you generally need to replace your existing 16K system ROM (IC4 on Issue 3 boards) with an EPROM (e.g., 27128 or 27256) burned with the diagnostic image. Comprehensive RAM soak tests, ULA timing, keyboard matrix,
Desolder the original Sinclair ROM (if it isn't already socketed). Solder an IC socket in its place.