The Spectrum’s ULA (an early gate array) is responsible for generating the video signal and handling RAM contention with the CPU. The test program checks the ULA by writing patterns to the screen memory area ( 0x4000 to 0x57FF in a 48K model).
Here are the most trusted diagnostic ROM images used by the community for servicing 16K, 48K, and 128K Spectrums. 1. Retroleum ZX Spectrum Diagnostic ROM (Phil Ruston) zx spectrum test program link
If you are serious about Spectrum repair, consider investing in a Diagnostic ROM Cartridge (like the SMART Card or the ZXC4). Having the test program on a physical cartridge that plugs into the expansion port is much more reliable than trying to load a tape into a broken computer! The Spectrum’s ULA (an early gate array) is
If you are looking for programs to test hardware functionality (RAM, ROM, keyboard, ULA), these are the primary links: If you are looking for programs to test
Depending on the state of your ZX Spectrum, you will need to choose one of two methods to execute a test program:
Install the diagnostic chip into the ROM socket of the Spectrum. Upon powering on, the screen will display a detailed map of working and failed RAM chips.