Zx Spectrum Test Program Link Guide

This report outlines the primary diagnostic and test programs available for the Sinclair ZX Spectrum

. These tools range from official historical utilities used by repair engineers to modern diagnostic ROMs developed by the retro-computing community to troubleshoot hardware failures such as bad RAM, faulty ROMs, and keyboard issues. 1. Modern Community Standards The most recommended "test programs" today are typically Diagnostic ROMs

. These are flashed onto external cartridges or ROM replacement boards and are essential when a Spectrum won't boot into BASIC. Brendan Alford’s ZX Diagnostics:

This is currently one of the most popular functional testing suites for hardware clones and original machines. It is an open-source project available on

that tests memory banks, paging, and keyboard functionality. Retroleum DiagROM (Phil Ruston):

A widely used diagnostic image for the Spectrum 16/48 and 128K models. It can be found at

and provides visual border patterns and audio beeps to identify faulty RAM chips even if the screen is unreadable. 2. Historical & Official Test Programs

Sinclair Research produced several official utilities, some of which were originally restricted to authorized service technicians. Sinclair ZX Spectrum Test ROM (1983):

An unpublished ROM used by engineers for hardware verification. It occupies only 8KB and is a common target for those looking for the "original" diagnostic feel. Sinclair Test Program (1985): zx spectrum test program link

A later utility released by Sinclair Research for the 48K and Spectrum+. It was designed to check keys not present on the original models and was often supplied via Microdrive or cassette. World of Spectrum 3. Usage & Implementation

Test programs for the Spectrum are usually loaded in one of two ways: Sinclair ZX Spectrum Test ROM

For those maintaining or repairing classic Sinclair hardware, several essential ZX Spectrum test programs and diagnostic ROMs are available to troubleshoot memory, ULA, and other hardware issues. Top Recommended Diagnostic ROMs & Tools

These programs are the gold standard for identifying faulty RAM chips or hardware failures. Retroleum DiagROM (Phil Ruston)

: A highly regarded diagnostic tool for testing RAM (16K, 48K, and 128K), ULA, and other system features. It is often included in modern hardware like the Retroleum SMART Card Brendan Alford ZX-Diagnostics : Open-source firmware available on

designed for functional testing of ZX Spectrum hardware and clones. Official Sinclair Test Programs : Originally for repair engineers, these include the Sinclair ZX Spectrum Test ROM (1983) and the Sinclair Research Test Program (1985) for I/O handling. Alioth Spectrum Flash ROM & Diagnostics : Offers downloadable ROMs, source code, and TZX format files

for programming diagnostic tools directly into flash memory. Where to Download or Purchase

Depending on whether you prefer to run a digital file via an emulator or use physical hardware, you can find resources at these locations: This report outlines the primary diagnostic and test

ZX Spectrum 16k 48k 128k +2 +3 Diagnostic Test Cartridge - External Test ROM

4. Creating a Test Program: Minimal Example Outline

A simple 48K Spectrum test program typically includes:

• A small bootstrap in UDG-friendly ASCII or an assembler source (.asm)
• Initialization that sets up the screen and clears attributes
• A memory test routine that writes known patterns (0x00, 0xFF, 0x55, 0xAA) across RAM and verifies reads
• A basic tape save/load roundtrip test: save a short block to tape and attempt to load it back
• A keyboard echo or port test
• An options menu to run specific tests

High-level steps to build such a program:

1. Choose assembler (z80asm, sjasmplus, Pasmo, or WinAPE built-in tools).
2. Implement test routines in Z80 assembly (or compile from Sinclair BASIC with machine code).
3. Create a TAP/ZIP or TZX image using tools (MakeTZX, tapir, or emulator export).
4. Document expected results and known limitations.

Example test routines (described, not code):

• Memory test: write 0x55 then read back; write 0xAA then read back; report first failing address.
• Border timing: toggle border on each frame and count frames with a loop to estimate frame timing.
• Beeper test: POKE to the speaker port with a delay loop to create a tone; verify audible output.
• Keyboard matrix: poll each row and display pressed keys; used to confirm keyboard wiring.

(If you want actual assembler source, say so and specify target machine: 48K, 128K, or a particular clone.)

Modern Resurrection: The Diag Board

In the modern retro-computing scene, the "Test Program Link" has evolved into a dedicated hardware tool known as the ZX Diag Board.

This is a physical cartridge that plugs into the Spectrum’s expansion port. It contains a test program that runs automatically, bypassing the potentially broken keyboard and fragile tape loading mechanism.

The Diag Board represents the ultimate realization of the test link concept. It doesn't just check RAM; it systematically tests: A small bootstrap in UDG-friendly ASCII or an

• The Z80 CPU: Verifying instruction sets.
• The ULA: Checking video timing and border colors.
• The 4116/4532 DRAM: Identifying stuck bits in lower and upper memory.
• The Keyboard Matrix: Scanning for short circuits.

The output is often displayed on the screen in color-coded bars. If the screen is too corrupted to read, the Diag Board sometimes outputs a link to a speaker, beeping error codes like a Morse code distress signal from a silicon shipwreck.

1. What is a “Test Program” for the ZX Spectrum?

A “test program” is a small piece of software designed to verify hardware, software interfaces, or specific system behaviors. On the Spectrum, test programs historically served several purposes:

• Hardware diagnostics — verifying RAM, ROM paging (on 128K machines), keyboard matrix, display output, ULA timings, and I/O ports
• Loader test — confirming that tape or disk loading routines work reliably under various conditions
• Peripheral tests — checking Kempston/Ajnar/Interface 2 joystick ports, printers, parallel/serial interfaces, disk interfaces (e.g., Beta Disk, Opus Discovery), and modern AT interfaces
• Sound tests — exercising the beeper or AY-3-8912 chip (on 128K models)
• Performance benchmarks — measuring CPU speed, memory copy throughput, or rendering rates
• Development harness — quick harnesses to exercise new routines or modules during development
• Format and compatibility tests — ensuring programs will load across different Spectrum variants, clones, and emulators

A “test program link” commonly refers to a packaged or documented way to obtain, load, or chain (link) one or more test programs together — either as a loader that sequentially runs multiple tests, or as a link/reference (URL/archive) pointing to test program resources.

How to Load the Test Program (Three Methods)

You have your link. You downloaded zx-tester-v23.tap. Now what?

Step-by-Step: Running the Diagnostics

Once the program loads (you will see a cyan screen with "ZX Spectrum Diagnostic v2.3"), follow this sequence:

1. RAM Test (The most critical)

   • The program will test RAM banks 0-7 (up to 128K).
   • Pass: Displays green "OK" for each bank.
   • Fail: Displays a red address (e.g., 40960). This maps directly to a chip. Example: $4000 error is usually IC23 or IC24.

2. Keyboard Matrix Test

   • A grid appears representing each key press.
   • Short every key with your finger. If a key doesn't light up, you have a membrane failure—not a ULA issue.

3. ULA vs. Contended Memory Test

   • This checks the "contention" timing unique to the Spectrum. A failure here means your ULA (socketed on Issue 2 and 3 boards) is dying.

4. Sound and Beeper Test

   • It will play three tones. If you hear nothing, check the EAR/MIC socket or the internal transistor (TR1, TR2 on 48K boards).

5. Video Output Test (The coloured bars)

   • The program cycles through the eight Spectrum colours. If you see missing colours or snow, your composite mod or RF modulator needs attention.

9. Example Test Suite Structure (Suggested Files & Contents)

• README.txt — plain text with instructions, expected results, supported machines
• test-suite.tzx — TZX container with chained test blocks and loader stub
• menu.tap / menu.tzx — simple menu program for selecting and running tests
• memtest.48k — memory test program for 48K machines
• aytest.128k — AY sound chip test for 128K machines
• io_test.tap — joystick/parallel/serial test
• disk_tests.trd — disk-based tests and menu
• source/ — assembler sources for each test
• docs/ — design notes, known issues, changelog