| Error Message | Likely Fault | Fix | | :--- | :--- | :--- | | RAM 0 BIT 0 FAIL | Lower 16K bank, Chip IC6 (D0 data line) | Replace 4116 or 4532 DRAM | | CONTENTION FAIL | ULA pin 28 (Contention logic) | Replace ULA (5C112E or 6C001E-7) | | ROM CHECKSUM: BAD | Corrupted ROM or address line short | Re-burn ROM or check CPU A14/A15 lines | | EXTERNAL BUS: FLOATING | Broken track between CPU and ULA | Inspect data bus (D0-D7) continuity | If you are repairing Spectrums professionally, you need the burnable ROM version . The tape-based test is fine, but if your Spectrum cannot read tapes (common due to failed capacitors), you are stuck.
Stop replacing random chips. Stop reflowing solder joints blindly. Download the diagnostic, load it via your preferred method, and let the machine tell you exactly what is broken. zx spectrum test program link
If you own a Sinclair ZX Spectrum—whether it’s a pristine 48K rubber-key, a battle-hardened 128K Toastrack, or a modern clone like the Harlequin—you know one universal truth: these machines are nearly 40 years old. Capacitors leak. RAM chips fail. The ULA (Uncommitted Logic Array) gets finicky. | Error Message | Likely Fault | Fix