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Fujitsu FM-7 / FM-8 (& FM77)

Fujitsu's 6809 line (FM-8 in 1981, FM-7 in 1982) — a dual-6809 architecture (main CPU + video sub-CPU), popular in Japan for 8-bit games before the FM Towns. Standard JP 8-bit repair: recap, drive, keyboard.

Fujitsu FM-New7 (série FM-7)

Fujitsu FM-New7 (série FM-7) — photo by JCCyC, CC BY-SA 3.0 (Wikimedia Commons).

Identification

Model Year Note
FM-8 1981 dual 6809, optional bubble memory
FM-7 1982 consumer version, the gaming reference
FM77 / FM77AV 1984-85 built-in floppy, AV = 4096 colors, FM sound

CPU: two Motorola 6809 (main + video); Sound: PSG (AY-3-8910) then FM (YM2203) on AV; RGB output; cassette / floppy.

Clocks & frequencies ✅

Component Frequency Role / scope
Motorola MC68B09 2 MHz CPU principal
Motorola MC68B09 2 MHz second 6809 dédié au graphisme
Zilog Z80 — en option, sur carte d'extension enfichable

The FM-7 is a twin 6809 at 2 MHz machine: a main processor and a separate graphics processor. A purely video symptom can therefore come from the second 6809 while the main one is fine.

Why this matters in repair

A clock that is missing or off-value on a frequency counter points straight at the crystal, its divider chain or the component it feeds — the fastest starting point on a machine that will not boot. Source: Wikipedia (CC-BY-SA).

Repair (technician)

  • Recap (PSU + board) → Recap.
  • Floppy drive (FM77): mechanism / belts → clean, Gotek possible.
  • Dual 6809: on a crash, isolate main vs sub-CPU → substitution.
  • Keyboard: contacts → clean.
  • Video: RGB output / palette (AV) → check wiring.

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

Common faults

Symptom Likely cause Lead
Won't boot / freezes one of the two 6809 / RAM Isolate, substitute
Floppy not read mechanism / belt Clean / Gotek
Instability caps Recap
Dead keys keyboard Clean

Modernisation & mods — what to buy, how

Modern storage - FM77 (integrated drive): Gotek + FlashFloppy or HxC 🟡 → .d77 images from USB/SD. - FM-7/8 (cassette): load via audio 🟢 from a PC/phone; disk interfaces + Gotek 🟡.

Video - RGB output 🟢 → SCART then OSSC / RetroTINK or RGB2HDMI (the FM77AV outputs an extended palette) for crisp digital.

Reliability - Recap 🟠; change drive belts (FM77); on a crash, isolate the main 6809 from the sub-CPU (dual 6809) during diagnosis.

⚠️ 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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