Amstrad CPC 464 Maintenance Guide

CPC 464 with the CTM640 colour monitor, which holds the system's only power supply

Routine maintenance on the Amstrad CPC 464 centres on the cassette deck and its board, the keyboard, the connectors and the monitor that powers the machine. Fault diagnosis is in the Amstrad CPC 464 Troubleshooting Guide and component values are in the Amstrad CPC 464 Capacitor Replacement Guide. Part numbers and alignment figures are from Amstrad's service manual.

Power and safety

The CPC 464 has no mains connection and no power supply of its own. It takes 5 V DC through a socket on the back, which Amstrad's specification says is "supplied exclusively from screen", the CTM640 colour or GT64 green monitor.

• The keyboard unit carries no mains voltage. Work on it with the DC lead unplugged and anti-static precautions.
• The monitors contain the mains supply and a CRT, and hold a dangerous charge after switch-off. Read CRT Discharge Procedure before opening one.
• Amstrad's fault chart for a dead machine starts at the monitor: mains fuse, then the DC output and lead, then the computer.

Amstrad's safety test for the monitors is a 4 kV flash test between the mains lead (live and neutral joined) and all accessible metal, and an insulation test between the same points requiring at least 4 MΩ.

Identifying your board

CPCWiki's catalogue of photographed boards identifies four CPC 464 main board versions by their silkscreened part number.

CPC 464 main board versions

Version	Silkscreen	Size	Notes
1 (©1983)	Z70100; 270100 MC0001A; Z70100 MC0001A	405 × 155 mm	Gate array under a cooling plate, its VCC2 fed through R138 and R139; keyboard wired to the board on the first boards
2 (©1984)	Z70200 with MC0001A, MC0002A–D, MC0003A, MC0008B–D	405 × 152 mm	Pads for both the old and new gate array; connector for the 6128-style 2 × 10-pin membrane keyboard
3	Z70374 MC0044A/B, Z70375 MC0044D, Z70378 MC0046A	240 × 150 or 238 × 145 mm	Same parts packed more tightly; joystick and stereo sockets on the left
4, cost-down (©1988)	Z80329 MC0099A	237 × 108 mm	100-pin surface-mount ASIC (Amstrad 40226) combining the gate array, CRTC and some floppy, DRAM and reset logic

On the original board Amstrad's parts list gives the gate array as IC116, 20RA043, part 40007. CPCWiki lists 40007 and 40008 as the heat-sinked gate arrays and 40010 as the later one without a heat sink, with different pinouts.

Opening the unit

1. Switch off and unplug the DC lead from the monitor.
2. Disconnect any joystick, printer or expansion-port device.
3. Lay the keyboard unit face down on a soft cloth and remove the screws from the underside.
4. Lift the case apart, minding the keyboard cable, and photograph the cable routing before you unplug anything.
5. Disconnect the keyboard cable and the cassette board's 8-way connector, CD001.

Amstrad's cassette PCB drawing labels the CD001 conductors: 1 +B (red), 2 GND (black), 3 +B (white), 4 DATA IN (blue), 5 DATA OUT (green), 6 SOUND IN (white), 7 PLAY ON (yellow), 8 INPUT.

The cassette PCB (PCB301) carries the audio and tape electronics: IC301 (LA4140), IC302 (LA6324 quad op-amp), the tape motor relay RY301, the 300-series resistors and twelve of the fourteen electrolytic capacitors. The volume control VR301 is on the small board PCB302 beside it. Audio and tape faults are usually on these boards.

Cleaning

• Brush and low-pressure air for the main board, keyboard mat and cassette mechanism.
• Clean the record/play head (part 170201), capstan and pinch roller with isopropyl alcohol on a foam swab.
• Clean the sockets J101 to J104 with a little contact cleaner on a swab.
• Clean the rubber contact mats (parts 170008 key mat, 170009 digit mat, 170010 spacer) with a damp lint-free cloth.

Keyboard

The keyboard has 74 keys: QWERTY with a numeric cluster, cursor and copy cursor, large enter, shift, caps lock, tab, escape, delete, clear and control. It is built from keytops, the rubber contact mats and a contact PCB in two halves (parts 170028 and 170029). Amstrad's fault chart for keys that do not work sends you to inspect the keyboard PCB for cracks, liquid spillage and distorted mounting, and then to check the connector lead and its termination.

Cassette deck

CPC464 cassette mechanism, service parts (p. 6)

Part	Amstrad part no.
Main belt	170204
R/P head	170201
Erase head	170202
Pinch roller assembly	809162
Spring, pinch roller	809161
Flywheel	809156
Idler assembly	809155
Idler gear	809173
Motor	170208
Motor pulley	170211
Counter belt (cabinet list)	170014
Cassette mechanism, complete (cabinet list)	170012

When the motor runs but the capstan does not turn, check the main belt (170204). Amstrad gives only the part number, not the belt's dimensions, so measure the pulleys before ordering a generic belt, and clean any residue of the old belt off the pulleys first.

Azimuth adjustment

Amstrad's procedure needs a test tape recorded with a constant 6 kHz tone and a valve or electronic voltmeter:

1. Set the volume on the CPC 464 to maximum.
2. Connect the voltmeter to pin 7 of IC302 on the cassette PCB.
3. Play the test tape and turn the azimuth screw on the cassette head for a reading between 330 mV and 520 mV.

Speed check

Play a standard tape and check the output on an oscilloscope on the 100 µs range. Amstrad states that a speed variation of ±4% will not affect software loading. The manual gives no speed adjustment.

Testing the cassette board alone

To run the cassette module without the computer, connect 5 V DC across points B (−) and C (+) on the cassette PCB and link E to G and H to F; the deck then works in audio mode.

Amstrad's cassette fault chart

When tapes will not load, Amstrad's order is: check the connections to the tape deck, clean the tape head, check head alignment, check the switches on the cassette keys, and check the tape motor control relay. If software loads but behaves strangely, the fault is on the computer board, in the RAM or the ULA. A physically damaged tape will not load at all: "there will be no 'half' working programs."

Power input

The DC socket is J104, part 170024, described by Amstrad as a "5mm socket for CPC464 power supply". Grimware gives the input as 5 V at 2 A on a 2.1 mm plug. Check the polarity of any replacement supply against your own board before connecting it. On an unreliable machine, measure 5 V at J104 before suspecting anything on the board.

Connectors

CPC 464 external connectors

Ref	Amstrad description	Part no.	Notes
J101	DIN socket, 6 pin	170025	Monitor: 1 red, 2 green, 3 blue, 4 sync, 5 ground, 6 luminance
J102	Joystick socket, 9 pin	170023	1 up, 2 down, 3 left, 4 right, 5 fire 3, 6 fire 2, 7 fire 1, 8 ground, 9 ground for a second joystick
J103	Input/output socket, 3.5 mm	170022	Stereo sound output, intended for an amplifier rather than headphones
J104	DC jack socket	170024	5 V in from the monitor
Printer	PCB edge connector	–	Centronics-style; pin 9 is ground, so only seven data bits (D0–D6) are output
Expansion	PCB edge connector, 50 way	–	Pin 1 sound, 2 and 49 ground, 27 +5 V, 50 CPU clock (4 MHz); the DDI-1 disc interface plugs in here

Capacitors

The CPC 464 has fourteen aluminium electrolytic capacitors. Only C101 and C102, both 47 µF / 10 V, are on the main board; the other twelve are 300-series parts on the cassette PCB, the largest being C322, 470 µF / 10 V. Values, references and part numbers are in the Amstrad CPC 464 Capacitor Replacement Guide.

ROM

The operating system and Locomotive BASIC 1.0 are in a single 32 KB ROM at IC103, listed in the original parts list as TMM-23256P-1950. CPCWiki lists Amstrad's custom part numbers for the CPC 464 firmware ROM as 40009 (English), 40037 (Spanish) and 40050 (French). If the machine starts with corrupted characters or hangs, reseat IC103 before suspecting the chip.

DDI-1 disc drive

The DDI-1 and FD-1 drives each have their own mains supply, so they carry mains voltage even though the computer does not. The mechanism is a belt-driven Compact FDD EME-150A, and Amstrad lists the drive belt as part 190015. CPCWiki gives the replacement belt as 3 mm wide, 0.6 mm thick and 230 mm in outer circumference, and warns that the small write-protect pin can fall out when the drive is turned over.

Tools

• Cross-head screwdrivers and an anti-static strap
• Digital multimeter
• Isopropyl alcohol and foam swabs
• Oscilloscope, electronic voltmeter and a 6 kHz test tape for the azimuth and speed checks
• Replacement main belt, sized from your own pulleys
• Fine-tip soldering iron and desoldering braid
• See Recommended Tools for the general workshop kit.

Related pages

• Amstrad CPC 464 · Amstrad CPC 464 Troubleshooting Guide · Amstrad CPC 464 Capacitor Replacement Guide
• Amstrad CPC 464 Service Manual · Amstrad DDI-1 / FD-1 Service Manual
• Amstrad CPC 664 Maintenance Guide
• CRT Discharge Procedure · Capacitor Failure Symptoms · Recommended Tools