Sinclair ZX80 · ZX81 · QL¶
The Sinclairs other than the Spectrum: the ultra-cheap pioneers ZX80 (1980) and ZX81 (1981, 1 KB of RAM!), and the pro QL (1984, 68008, Microdrive). Standard Sinclair repair: a hot regulator, RAM, membrane keyboard.
Sinclair ZX81 — photo by Rama, CC BY-SA 2.0 fr (Wikimedia Commons).
Identification¶
| Model | Year | CPU | Note |
|---|---|---|---|
| ZX80 | 1980 | Z80 @ 3.25 MHz | all white, screen flickers while computing ("FAST/SLOW") |
| ZX81 | 1981 | Z80 | 1 KB RAM, single ULA, 16 KB "wobble" pack |
| QL (Quantum Leap) | 1984 | 68008 | 128 KB, two endless-loop Microdrives |
Repair (technician)¶
- 7805 regulator: runs very hot (ZX81) → heatsink / replace (the "unstable/dies when hot" fault).
- ULA (ZX81): sensitive custom chip → substitution (modern reissues exist).
- "RAM pack wobble" (ZX81 + 16 KB): bad contact at the rear connector → clean, brace, redo joints.
- Membrane keyboard: broken flex → membrane replacement (a common remade part).
- QL — Microdrive: degraded tapes and pressure pads → clean head, replace pad; sound-ULA caps.
- Light recap + check the external PSU → Recap.
Common faults¶
| Symptom | Likely cause | Lead |
|---|---|---|
| Crashes when the machine is moved | RAM pack wobble | Clean/brace the connector |
| Unstable / dies when hot | 7805 regulator | Heatsink / replace |
| No picture | ULA | Substitute |
| Dead keys | membrane | Replace the membrane |
| Microdrive unreadable (QL) | tape / pad | Clean, replace pad |
Modernisation & mods — what to buy, how¶
Fragile parts: ZX81 ULA, membrane, QL Microdrives
ZX81: a dead ULA is replaced by a reissue ("vLA/ZX8x"); remade membrane keyboard. QL: Minerva ROM (fixes bugs), revised 7805 regulator + heatsink; the Microdrives (endless-loop tapes) are the weak point → move to SD.
Modern storage
- ZX81: ZXpand 🟢 (edge-connector board) = SD reader (loads .p), 32/56 KB RAM and sometimes
AY sound → kills the cassette and the famous "RAM pack wobble". Otherwise audio from a
PC/phone 🟢 (.p → WAV).
- QL: QL-SD 🟢 (SD card in the ROM port), QUBIDE 🟡 (IDE/CF), or vDriveQL 🟢 which emulates
the Microdrives; Gotek + FlashFloppy 🟡 via a disk interface.
Video - ZX81: UHF output → composite mod 🟡 (sharp on a modern display), then RGB2HDMI downstream. - QL: RGB output 🟢 → SCART then OSSC / RetroTINK or RGB2HDMI.
⚠️ Do not host ROMs/games — method only.
See also¶
- ZX Spectrum (the big brother) · Oric · Recap.
Sources & attribution¶
- Photo Sinclair ZX81 — Rama, CC BY-SA 2.0 fr, Wikimedia Commons — https://commons.wikimedia.org/wiki/File:Sinclair-ZX81-Rama.jpg
- Wikipedia — ZX80 / ZX81 / Sinclair QL (Z80/68008, ULA, Microdrive) — CC-BY-SA — https://en.wikipedia.org/wiki/ZX81
- Established Sinclair community knowledge (RAM pack wobble, 7805, membrane) — synthesis.
Review & corrections
How this space is used
Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.
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