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Jupiter Ace

The 1982 oddity designed by ex-Sinclair engineers (Vickers & Altwasser): instead of BASIC it runs FORTH — faster and more compact. Z80A, B&W, 1 KB of RAM, cassette. Rare and much sought-after. Standard 8-bit repair: recap, SRAM, membrane.

Jupiter Ace

Jupiter Ace — photo by Dutra de Lacerda, domaine public (Wikimedia Commons).

Identification

  • CPU: Zilog Z80A @ 3.25 MHz; 1 KB RAM (expandable 16/48 KB); FORTH ROM.
  • Video: B&W text/graphics → RF output (composite mod common).
  • TTL logic (no custom ULA like the Spectrum); ZX-style membrane keyboard.

Repair (technician)

  • Recap + check the external PSU → Recap.
  • 2114 SRAM (the 1 KB RAM): a frequent failure → substitution / test.
  • Membrane keyboard: broken flex → membrane replacement (a remade part).
  • TTL logic: diagnose by substitution (no ULA makes repair easier).

Procedure — a dead computer, step by step ✅

What this adds

Ordered for a home computer: what kills these is its power supply, its battery, its capacitors, its socketed RAM and its keyboard — roughly in that order, and well before the CPU. → PCB diagnosis

1. The power supply — measured before it is plugged in. This is the one step not to swap around. On a machine of this age a supply does not simply stop: a 5 V regulator that fails high puts 7, 9, 12 V onto the bus and takes the RAM and the custom chips with it. Measure every rail off the machine, under a dummy load if you can, and only then plug it in.

2. The battery, if it has one. Any RTC or backup cell soldered to a board is a future leak. If yours has one and it has never been changed, take it out before it takes the tracks with it. → Backup batteries

3. Capacitors. Recap is the default on these machines, not a last resort — and on the supply first, since that is what protects everything else. → Recap

4. RAM, on its sockets. These machines were built to be repaired: the RAM, and often the logic, sit in sockets. Reseat everything first — thirty years of oxide is a classic no-boot. Then swap chips: a bad RAM chip usually gives a repeatable pattern of garbage or a screen frozen at a fixed character.

5. The keyboard. A console does not have one; a computer's is a wear part. A membrane keyboard fails as whole dead rows or columns — that is the membrane, not the machine. A mechanical one wants its contacts cleaning, not replacing. Check this page: the failure mode is often documented per model.

6. Storage — tape or disk. Both often come down to the same things: a dirty head, and for tape the azimuth and a belt turned to tar. ⚠️ On the floppy side, check whether the mechanism actually has a belt before looking for one: many do, but some drives are direct drive, and hunting a belt that isn't there means stripping a drive for nothing. A machine that boots but loads nothing is a drive fault, not a logic fault — do not go looking on the board for it.

7. Video output. RF, composite, RGB or a dedicated monitor, depending on the machine (see Identification). Test with something else before you conclude: a period modulator and a modern TV disagree far more often than either is broken.

8. Still nothing. Now the logic: rails on the board, reset, clock, bus. → PCB diagnosis

Modernisation & mods — what to buy, how

  • RAM expansion (16/48 KB) remade 🟢: near-mandatory to make the machine actually usable (1 KB stock).
  • Storage: cassette via audio 🟢 (PC/phone); community SD interfaces 🟡.
  • Video: RF output → composite mod 🟡 for a crisp modern display.
  • Reproductions: remade boards / clones (e.g. the Ace-inspired "Minstrel") to preserve the platform without wearing out the original.
  • Reliability: light recap; clean keyboard/membrane.

⚠️ Do not host ROMs/software — method only.

See also

Sources & attribution

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.

Reading is open to everyone; posting requires signing in with Discord. Reports from the wiki's declared reviewers are handled first; anyone else's are read too, but go through a human before anything is changed.