The CPU is not executing the ROM. Check the Z80 CPU, clock crystal, and the EPROM wiring.
Causes crashes or graphical corruption when loading larger games.
Look for tools like TZX-Duino or MaxDuino firmware if you prefer using an SD card hardware link to load test programs instantly.
While the Sinclair test program is good, sometimes the machine is too broken to load software. In these cases, you need a (often called a Diagnostic ROM), which replaces the original Sinclair ROM with a testing suite. zx spectrum test program link
This is a comprehensive, open-source diagnostic suite. Based on the original work by Dylan Smith, it is a collaborative project aimed at providing a complete diagnostic tool for nearly every model, from the original ZX Spectrum 16K/48K to the later +2A and +3 models.
Quick plug-and-play testing without opening the case.
Technicians would often create a "Test Link" by bridging specific connections on the edge connector at the rear of the machine. For example, to test the upper memory, a technician might force the machine into a continuous write/read loop to a specific address range. By connecting an oscilloscope to the data lines (the link between the program and the hardware), they could visualize exactly where the signal was degrading. The CPU is not executing the ROM
| Type | How it loads | Best for | | :--- | :--- | :--- | | | Burned into an EPROM (e.g., 27C256) and replaces the original ROM. | Dead machines that won’t even boot to a border. | | Tape File (.TAP/.TZX) | Loaded via a phone/PC into the Spectrum’s EAR port. | Machines with a working border and basic boot. | | Snapshot (.SNA/.Z80) | Loaded via a DivMMC or SD card interface. | Machines with a working RAM top and an interface. |
: A comprehensive open-source diagnostic suite by Brendan Alford. It includes tests for the CPU, RAM, and keyboard [10].
Disclaimer: Repairing vintage electronics requires soldering skills. Always power down the unit before attempting repairs. If you'd like, I can: Look for tools like TZX-Duino or MaxDuino firmware
Some Spectrums are picky. Use (Windows/Linux) or Audacity (Mac/PC) to convert the TAP to a WAV file. Set parameters:
Traces crack over time, causing entire rows or columns of keys to stop responding.
If the test shows "Bank 0 Fail," you likely have a bad lower 16K chip (4116). These are notorious for dying due to voltage spikes.