Amstrad CPC 464

The Amstrad CPC 464 is a home computer introduced on 21 June 1984, with 64 KB of RAM and an integrated cassette deck in the keyboard unit. It was sold as a complete system with a monitor — £249 with the green GT64, £359 with the CTM640 colour monitor — and the monitor is not an accessory: it is where the machine's power comes from.

Amstrad CPC 464

CPC 464 with the colour monitor
Specifications
Developer	Amstrad
Manufacturer	Amstrad Consumer Electronics plc
Type	Home computer
Released	21 June 1984
Discontinued	1990
Intro price	£249 with green monitor / £359 with colour monitor
CPU	Zilog Z80A @ 4 MHz
Memory	64 KB RAM (over 42 KB available to the user)
Storage	Integrated cassette deck, 1000 or 2000 baud
Display	160×200×16, 320×200×4 or 640×200×2 from a 27-colour palette
Sound	General Instrument AY-3-8912, three voices
ROM	32 KB — OS and Locomotive BASIC 1.0
Power	5 V DC from the monitor. No mains connection and no internal power supply
OS / Firmware	Amstrad firmware with Locomotive BASIC 1.0
Successor	Amstrad 464 Plus
Model no.	CPC 464

The part numbers and specification figures on this page are Amstrad's own, from the CPC464 Micro Computer / CTM640 Colour Monitor / GT64 Green Monitor Service Manual hosted on this wiki.

The monitor is the power supply

The CPC 464 has no mains connection and no internal power supply. It takes 5 V DC through a socket on the back, and Amstrad's own specification says this is "supplied exclusively from screen system" — the CTM640 or the GT64. Mains enters the monitor, not the computer.

• The computer is safe to open. There is no mains voltage anywhere in the keyboard unit.
• The monitor is not. Both monitors contain a CRT with a lethal anode charge and mains-derived bulk capacitors that hold their charge after switch-off. See CRT Discharge Procedure.
• A "dead CPC" is very often a dead monitor. Amstrad's own fault chart sends you to the monitor's 5 V output and the DC cord before anything on the computer board.

There is no cooling fan. No fan or fan motor appears anywhere in Amstrad's parts lists; the machine is passively cooled.

Architecture

• CPU — Zilog Z80A at 4 MHz. The Gate Array inserts wait states so that video and CPU accesses do not collide, which is why measured throughput is below what a clean 4 MHz Z80 would give.
• RAM — 64 KB, of which Amstrad's specification says over 42 KB is available to the user. The video memory is part of the same 64 KB.
• ROM — 32 KB, holding the operating system and Locomotive BASIC 1.0.
• Video — a 6845 CRT controller with the Gate Array generating the pixel pipeline.
• Sound — General Instrument AY-3-8912, three voices, eight octaves in Amstrad's wording for the 664 and seven for the 464.
• I/O — an 8255 parallel interface for the keyboard, the AY control lines and the cassette motor.

The Gate Array on the original board is IC116, marked 20RA043, Amstrad part number 40007, and it is the version with a cooling plate. Later boards use different Gate Array parts, and the final cost-down board replaces it entirely.

Display

Three modes, all 200 lines, from a 27-colour palette:

Video modes

Mode	Resolution	Colours	Text
0	160 × 200	16	20 columns
1	320 × 200	4	40 columns
2	640 × 200	2	80 columns

There is no 640 × 400 mode. The CPC's vertical resolution is 200 lines in every mode.

Board versions

The main PCB went through four broad versions, identified by the silkscreened part number. The chip set, the board size and the keyboard connector all differ.

Amstrad CPC 464 main PCB versions

Version	Silkscreen	Size	Notes
v1 (©1983)	Z70100 (no MC code), 270100 MC0001A, or Z70100 MC0001A	405 × 155 mm	Gate Array with a cooling plate; VCC2 fed through R138/R139
v2 (©1984)	Z70200 with MC0001A, MC0002A/B/C/D, MC0003A, MC0008B/C/D	405 × 152 mm	Solder pads for both the old and the new Gate Array; 6128-style 2 × 10-pin dual-foil keyboard connector
v3	Z70374 MC0044A, Z70374 MC0044B, Z70375 MC0044D, Z70378 MC0046A	240 × 150 / 238 × 145 mm	Same parts packed tighter; joystick and stereo sockets moved to the left
v4 cost-down (©1988)	Z80329 MC0099A	237 × 108 mm	100-pin SMD ASIC (part 40226) combining the Gate Array, CRTC and some FDC, DRAM and reset logic

Z70373 and "28032" are not CPC 464 board numbers. Neither appears in Amstrad's documentation or in CPCWiki's catalogue of observed boards; the real numbers are the ones above.

Z70200 is a CPC 464 board. If you are looking at a machine with a disc drive and a Z70200 silkscreen, something has been swapped — the Amstrad CPC 664 board is Z70205.

Storage

An integrated cassette deck running at 1000 or 2000 baud, selectable from software. The mechanism and its alignment instructions are in Amstrad's manual; the deck has its own sub-PCB.

Almost the whole capacitor problem on this machine is on the cassette board. Amstrad's parts list gives fourteen electrolytics across the machine, and only C101 and C102 are on the main PCB — the other twelve are 300-series parts on the cassette PCB. Values are on Amstrad CPC 464 Capacitor Replacement Guide.

Servicing

• Amstrad CPC 464 Maintenance Guide — board identification, opening the unit, the cassette deck and its alignment, cleaning
• Amstrad CPC 464 Troubleshooting Guide — Amstrad's own hardware and software analysis charts
• Amstrad CPC 464 Capacitor Replacement Guide — Amstrad's complete electrical parts list
• Amstrad CPC 464 Service Manual — the document itself

Related pages

• Amstrad CPC 664
• Amstrad CPC 464 Maintenance Guide
• Amstrad CPC 464 Troubleshooting Guide
• Amstrad CPC 464 Capacitor Replacement Guide
• CRT Discharge Procedure