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Sord M5

Sord's little Japanese Z80 (1982) — the same hardware trio as the SG-1000 / ColecoVision (TMS9918A + SN76489), in a cartridge-computer form. Sold in the UK (CGL M5) and very popular in Czechoslovakia. Standard 8-bit repair: recap, contacts, PSU.

Sord M5 (CGL M5)

Sord M5 (CGL M5) — photo by liftarn, CC BY-SA 2.0 (Wikimedia Commons).

Identification

  • CPU: Zilog Z80A @ 3.58 MHz; low RAM (4 → 20 KB with expansion).
  • Video: TMS9918A (MSX/ColecoVision VDP) → RF/composite; Sound: SN76489.
  • Media: cartridge (BASIC-I/G/F, games) + cassette; rubber keyboard.

Repair (technician)

  • Recap (PSU + board) → Recap.
  • Cartridge contacts: oxidation → clean the connector (the #1 "won't start" cause).
  • Rubber keyboard: contacts / membrane → clean.
  • VDP / RAM: substitution on a partial picture (VDP shared with MSX/Coleco).
  • PSU: period regulation → service.

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

  • Storage: multi-game cartridges / M5 flashcarts 🟢; community SD solutions 🟡; cassette → audio 🟢 from a PC/phone.
  • Video: RF output → composite mod 🟡; the TMS9918A VDP suits RGB mods 🟠, even a F18A VDP replacement 🟠 (remove the VDP) for crisp digital VGA/RGB.
  • Reliability: light recap; clean cartridge contacts.

⚠️ Do not host ROMs/games — 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.

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