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Amstrad CPC (464 / 664 / 6128)

Amstrad's all-in-one 8-bit (1984), huge in France and Spain: a Z80, a house Gate Array, a CRTC 6845, AY-3-8912 sound, and a bundled monitor that powers the computer. Standard CPC repair: 3″ drive belt, membrane, monitor PSU, recap. The cartridge/console version is the GX4000.

Amstrad CPC 464

Amstrad CPC 464 — photo by Bill Bertram, CC BY-SA 2.5 (Wikimedia Commons).

Identification / models

Model Year Media RAM Note
CPC 464 1984 built-in tape 64 KB the best-seller
CPC 664 1985 3″ disk 64 KB short-lived (replaced by the 6128)
CPC 6128 1985 3″ disk 128 KB the flagship

Bundled with a monitor: CTM640 (colour RGB) or GT65 (green). The range evolves into the CPC Plus (1990, ASIC + cartridge).

Architecture

Block Chip Role
CPU Zilog Z80 @ 4 MHz logic
Video Gate Array + CRTC 6845 3 modes (160/320/640×200), 27-colour palette
Sound AY-3-8912 (3-channel PSG) music/SFX
Power from the monitor (5 V + 12 V for the drive) no internal PSU

Repair (technician)

3″ disk drive (664/6128) — the No. 1 fault

The rubber belt perishes over time (sticky residue) → disk won't spin / errors. Replace the belt (square section), clean the pulley and the head (IPA). See traces & vias / mechanics.

  • 3″ media (Amsoft/Maxell) rare and expensive → Gotek (Amstrad firmware) / HxC for preservation.
  • Power = the monitor: no boot? Check the voltage coming from the monitor (the CTM has its own caps to recap) before suspecting the computer.
  • Membrane keyboard: dead keys = tired membrane / cut trace (conductive repair).
  • Gate Array / CRTC: corrupt video = Gate Array / CRTC / RAM → substitution.
  • Targeted recap if picture/sound degrade → Recap.

Original service manual ✅

Manufacturer manual archived locally. It typically carries the schematics, the block diagram, the expected voltages and waveforms, the parts list and the disassembly procedures — the reference when a symptom matches no known fault.

  • Amstrad CPC664 — service manual (1985) — PDF

Status

A manufacturer document with no explicit licence, kept for preservation (machine long out of production). Source: Internet Archive.

Common faults

Symptom Likely cause Lead
Disk not read (664/6128) perished belt / head Replace belt, clean
Nothing at power-up monitor PSU / fuse Check monitor→board voltage
Dead keys keyboard membrane Replace the membrane
Corrupt video Gate Array / CRTC / RAM Substitute, RAM test
Wrong/no sound AY-3-8912 Sound-stage diagnosis

Modernisation & mods — what to buy, how

CTM monitor = CRT high voltage + 3″ belt

The original CTM monitor is a CRT (the CPC's power comes through the monitor): high voltage, discharge the tube before any work → CRT safety. The recap covers the base unit and the CTM monitor/PSU. On the 3″ drive, a dried belt is the #1 cause of unreadable disks → replace it.

Modern storage - Gotek + FlashFloppy or HxC 🟡: replace the 3″ drive (rare CF2 disks) — internal drive connector, DSK images from USB. - M4 board 🟢 (ROM/SD + Wi-Fi), Dandanator 🟢, X-MEM 🟡 (RAM+ROM) on the expansion port; C4CPC 🟢 = SD cartridges for the CPC Plus / GX4000.

Video - RGB output on the monitor connector 🟢 → SCART (Amstrad pinout) then OSSC / RetroTINK or RGB2HDMI.

Reliability: clean the keyboard/contacts.

⚠️ Do not host ROMs/disks — 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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