If your Spectrum is so dead it cannot load from tape, you need a hardware-based solution. In this case, a ZX Spectrum test program link is not a file but a physical EPROM.
This is the ultimate solution for professional repair shops.
The test program is a masterclass in constrained debugging. It must run without relying on the very subsystems it is testing. Here is a deep look at its core modules: zx spectrum test program link
Once the program loads (you will see a cyan screen with "ZX Spectrum Diagnostic v2.3"), follow this sequence:
Keyboard Matrix Test
ULA vs. Contended Memory Test
Sound and Beeper Test
Video Output Test (The coloured bars)
This is the gold standard for Spectrum diagnostics. It is often what people mean when they ask for a "test program." If your Spectrum is so dead it cannot