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NEC PC-8001 & PC-6001

NEC's beginnings before the PC-88/98: the PC-8001 (1979), NEC's first successful computer (Z80, a business/hobby reference in Japan), and the PC-6001 (1981, the consumer "papa" — color VDG + PSG sound). Standard JP 8-bit repair: recap, keyboard, PSU.

NEC PC-6001

NEC PC-6001 — photo by Darklanlan, CC BY 4.0 (Wikimedia Commons).

Identification

Model Year CPU Video / Sound Note
PC-8001 1979 µPD780 (Z80) text/graphics, mono NEC's first hit; mkII 1983
PC-6001 1981 µPD780 (Z80) MC6847 (VDG) + PSG AY-3-8910 consumer, color ("PC-6001 mkII/SR")

Media: cassette, floppy via external units (PC-8031…), cartridge (PC-6001); RF/composite (PC-6001), RGB/mono per model.

Clocks & frequencies ✅

Component Frequency Role / scope
NEC μPD780C-1 4 MHz CPU du PC-8001 — compatible Z80 ; 16 Ko de RAM extensible à 32 Ko
NEC μPD780C-1 3.8 MHz CPU of the PC-6001 — the same Z80 clone as the PC-8001, clocked lower

Both machines use the μPD780C-1, NEC's Z80 clone, but not at the same clock: 4 MHz on the PC-8001, 3.8 MHz on the PC-6001. Same part number, two different crystals — check which one you have before calling a clock out of spec.

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.
  • Keyboard: contacts / membrane → clean.
  • PSU: period regulation → service.
  • Cartridge contacts (PC-6001): clean.
  • Socketed RAM / ROM: substitution on a dead screen.

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: cassette → audio 🟢 from a PC/phone; community SD solutions on the expansion bus 🟡; floppy → Gotek + FlashFloppy 🟡 on external-FDD configs (PC-8001 mkII + PC-8031).
  • Video: RF output (PC-6001) → composite mod 🟡; RGB → OSSC/RGB2HDMI 🟢 for crisp digital.
  • Reliability: recap 🟠; check battery/RTC if present; clean 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.

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.