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This guide documents preventive maintenance procedures for the '''[[Amstrad CPC 464]]''' (1984&ndash;1990), covering the main PCB, the integrated cassette deck, the keyboard membrane, the CTM-640 / CTM-644 / GT-64 / GT-65 monitor that supplies its power, and the DDI-1 / FD-1 external floppy drive option. The CPC 464 is a fan-cooled-by-design 8-bit system with no internal mass storage other than the tape deck; most preventive maintenance therefore focuses on cleaning, contact integrity, the keyboard membrane and the integrated cassette mechanism.
[[File:Amstrad CPC 464 with CTM 640.jpg|thumb|right|300px|CPC 464 with the CTM640 colour monitor. The monitor contains the computer's only power supply โ€” and the only mains voltage in the system.]]
Preventive maintenance for the '''[[Amstrad CPC 464]]''' (1984), covering the main PCB, the cassette sub-PCB and deck, the keyboard, the monitor that supplies the machine's power, and the connectors. Fault diagnosis is in the [[Amstrad CPC 464 Troubleshooting Guide]]; component values are in the [[Amstrad CPC 464 Capacitor Replacement Guide]].
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Part numbers, circuit references and alignment figures on this page are Amstrad's own, from the [[Amstrad CPC 464 Service Manual]] hosted on this wiki.<ref name="sm464">Amstrad Consumer Electronics plc, ''CPC464 Micro Computer / CTM640 Colour Monitor / GT64 Green Monitor Service Manual''. Hosted at [[Amstrad CPC 464 Service Manual]]. Source for the technical specification (page 2), the CPC464 Cabinet Parts List (page 2), the Cassette Mechanism Parts List and Cassette Deck Alignment Instructions (page 6), the Cassette PCB layout (page 7), the Basic Hardware Analysis flow chart (page 9), the Cassette &amp; Software Analysis chart (page 10) and the CPC464 Electrical Parts List (page 17).</ref>
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== The monitor is the power supply ==
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'''The CPC 464 has no mains connection and no internal power supply.''' The machine takes 5 V DC through a DC socket on the back, and Amstrad's own specification states that this is "supplied exclusively from screen system" โ€” the CTM640 colour monitor or the GT64 green monitor.<ref name="sm464" /> Mains enters the ''monitor'', not the computer.
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That changes how you approach a dead machine, and it changes the hazards:
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* '''The computer itself is safe to open.''' There is no mains voltage anywhere inside the keyboard unit. You can work on the main PCB, the cassette PCB and the keyboard with the DC lead disconnected and nothing worse than static to worry about.
* '''The monitor is not.''' The CTM640 and GT64 contain a CRT with a lethal anode charge and mains-derived bulk capacitors that hold charge after switch-off. Read [[CRT Discharge Procedure]] before opening either.
* '''A "dead CPC" is very often a dead monitor.''' Amstrad's own fault-finding chart sends you to the monitor's 5 V supply and the DC cord before anything on the computer board.<ref name="sm464" />
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Amstrad's safety-test specification for the monitors, for reference: a flash test at '''4 kV''' between the mains lead (live and neutral joined) and all accessible exterior metal, and an insulation-resistance test on the same points showing at least '''4 Mฮฉ'''.<ref name="sm464" />
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== Identifying your board ==
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The CPC 464 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.<ref name="cpcwikimb">[https://www.cpcwiki.eu/index.php/Mainboard_Versions "Mainboard Versions"], CPCWiki. Community catalogue of silkscreen markings, board dimensions, copyright dates and per-version changes for the CPC 464, 664 and 6128 main boards. Secondary source, compiled from observed boards.</ref>
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{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''Amstrad CPC 464 main PCB versions'''<ref name="cpcwikimb" />
! Version !! Silkscreen !! Size !! Notes
|-
| '''v1''' (ยฉ1983) || Z70100 (no MC code), 270100 MC0001A, or Z70100 MC0001A || 405 ร— 155 mm || Gate Array with a cooling plate; VCC2 fed through R138/R139
|-
| '''v2''' (ยฉ1984) || Z70200 with MC0001A, MC0002A/B/C/D, MC0003A, MC0008B/C/D || 405 ร— 152 mm || Separate solder pads for both the old and the new Gate Array; 6128-style 2 ร— 10-pin dual-foil keyboard connector
|-
| '''v3''' || Z70374 MC0044A, Z70374 MC0044B, Z70375 MC0044D, Z70378 MC0046A || 240 ร— 150 / 238 ร— 145 mm || Same parts packed tighter; joystick and stereo sockets moved to the left side
|-
| '''v4''' "cost-down" (ยฉ1988) || '''Z80329 MC0099A''' || 237 ร— 108 mm || 100-pin SMD ASIC (part 40226) combining the Gate Array, CRTC and some FDC, DRAM and reset logic
|}
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On the original board Amstrad's own parts list gives the Gate Array as '''IC116, marked 20RA043''', Amstrad part number 40007.<ref name="sm464" />
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== Opening the unit ==
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Tools: a Philips screwdriver and an anti-static strap.
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# Switch off and unplug the DC lead from the monitor.
# Disconnect any joystick, printer or expansion-port peripheral.
# Lay the keyboard face-down on a soft cloth and remove the underside screws. The count varies by board version; some are hidden under the model-name label.
# Lift the lower half of the case.
# Disconnect the keyboard cable. On v1 boards this is discrete wiring โ€” '''photograph the colour order before you unplug anything'''. From v2 onward it is a 2 ร— 10-pin dual-foil connector.<ref name="cpcwikimb" />
# Disconnect the cassette PCB at '''CD001''', the 8-way connector on the cassette board. Amstrad labels the conductors on the PCB layout: 1 INPUT, 2 PLAY ON (yellow), 3 SOUND IN (white), 4 DATA OUT (green), 5 DATA IN (blue), 6 GND (black), 7 +B (white), 8 +B (red).<ref name="sm464" />
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'''Almost all the analogue electronics are on the cassette PCB, not the main board.''' It carries IC301 (LA4140 audio power amplifier), IC302 (LA6324 quad op-amp for the cassette read chain), VR301 (the 20 kฮฉ volume control), RY301 (the tape motor relay), SP301 (the speaker), L301, D301, D302 (the red power LED, SLP-145B) and the whole 300-series resistor and capacitor population.<ref name="sm464" /> If you are chasing an audio or tape fault, that is the board you want.
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== Regular cleaning ==
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* Soft brush and low-pressure air for the main PCB, the keyboard mat and the cassette mechanism. Hold the cassette flywheel by hand if you use air near it.
* Clean the R/P head (Amstrad part '''170201'''), capstan and pinch roller with IPA on a '''foam''' swab. Cotton fibres left in the head gap are a known cause of intermittent reads.
* Clean the connectors โ€” the 6-pin DIN video socket J101, the 9-pin D joystick socket J102, the 3.5 mm socket J103 and the DC socket J104 โ€” with contact cleaner sparingly on a foam swab.<ref name="sm464" />
* Clean the keyboard rubber contact mats (Amstrad parts '''170008''' key board mat, '''170009''' digit mat, '''170010''' spacer) by rolling them gently in a damp lint-free cloth. Do not soak the silicone in solvents.


== Safety Warning ==
== Keyboard maintenance ==


The CPC 464 system unit itself is powered from a regulated '''5 V DC, 2 A''' supply on a 2.1 mm centre-positive jack from the matching monitor. The system unit can be opened, cleaned and serviced without high-voltage risk.
The CPC 464 keyboard is a '''74-key''' assembly in QWERTY layout with a numeric cluster, cursor and copy cursor, large enter, shift, caps lock, tab, escape, delete, clear and control.<ref name="sm464" /> It is built up from keytops, silicone rubber contact mats (170008/170009/170010) and a flexible contact PCB in two halves (Amstrad parts '''170028''' and '''170029''').<ref name="sm464" />


The '''CTM-640 / CTM-644 colour monitor''', the '''GT-64 / GT-65 green monitor''' and any third-party CRT contain a '''lethal CRT anode charge''' (10&ndash;25 kV) and mains-side bulk capacitors. Any work that opens the monitor case must follow CRT-safety procedure:
Common faults:


# Power off and unplug the monitor mains lead.
* '''A whole row dead''' โ€” a broken membrane trace, or a fault in the cable between the contact PCB and the main board. Reseat the cable first, then check continuity along the row's track.
# Wait at least 30 minutes for the CRT and the PSU bulk capacitor to bleed.
* '''A single key dead''' โ€” dirty contact. Clean the carbon pill on the silicone dome and its matching pad on the membrane with IPA on a swab. '''Do not abrade the pill''' โ€” it is a conductive coating, not metal, and rubbing it off is permanent.
# Discharge the CRT anode through a 1 Mฮฉ / 10 W resistor between the chassis ground and the anode cap (slide the resistor under the rubber boot).
* '''A single key permanently active''' โ€” a short on the membrane, usually an old liquid spill that crystallised between adjacent traces. Clean the area with IPA. Scoring the membrane between the pads to isolate the trace is a last resort.
# Discharge the PSU bulk capacitor through a 1 kฮฉ / 5 W resistor before working on the primary side.
* '''Soft keys, no click''' โ€” a collapsed silicone dome. Replace from a donor mat.
# Verify both discharges with a multimeter.


Monitor work is covered in the monitor-specific service manuals; this guide concentrates on the system unit, the keyboard, the cassette mechanism and the routine work that touches both monitor and system unit.
Amstrad's own fault chart for "do all keys operate?" sends you to inspect the keyboard PCB for '''cracks, liquid spillage and distorted mounting''', then to check the connector lead and its termination.<ref name="sm464" />


== Identifying Your Board Revision ==
== Cassette deck maintenance ==


The CPC 464 main PCB went through four revisions identified by the silkscreen part-number marking. The chip set and capacitor positions differ between revisions, so identification is the first step before any work.
The deck is a single-motor mechanism. Amstrad's parts list gives every wear item a number:<ref name="sm464" />


<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:85%; text-align:left;"
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''CPC464 cassette mechanism โ€” service-relevant parts'''<ref name="sm464" />
|+'''Amstrad CPC 464 main PCB revisions'''
! Part !! Amstrad part no.
! Revision !! Silkscreen part number !! Form factor !! Gate Array !! Keyboard cable
|-
| '''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
|-
|-
| Original (1984) || Z70100 / Z70100 &mdash; MC0001A || Full size || 40007 (Ferranti, heatsinked) || Discrete wires
| Motor || 170208
|-
|-
| Revision 1 (1984) || Z70200 &mdash; MC002B / MC002D || Full size || 40007 or 40010 (CMOS) || Ribbon cable
| Motor Pulley || 170211
|-
|-
| Revision 2 (~1986) || Z70373 / Z70374 &mdash; MC004B / MC0044A || Half size || 40007 or 40010 || Ribbon cable
| Counter Belt || 170014
|-
|-
| Revision 3 / "cost-down" (~1988) || 28032? &mdash; MC0099 || ~1/4 size || 40226 (combines GA + CRTC + glue) || Ribbon cable
| Cassette Mechanism (complete) || 170012
|}
|}


Original and Revision 1 boards have ICs in DIL sockets; Revision 2 and 3 boards typically have the ICs soldered directly. The Revision 3 board is the most compact and uses the combined 40226 ASIC, which is the same ASIC family that appears in the 6128 and the cost-reduced [[Amstrad CPC 464|464]]/6128 Plus.
* '''Main belt (170204)''' โ€” the usual failure. Thirty-plus-year-old originals are almost universally either liquefied into a sticky black residue on the pulleys or stretched beyond useful tension. Symptom: the motor runs but the capstan does not turn, and tapes will not load. Amstrad publishes no replacement dimensions, only the part number, so '''measure your own pulleys''' before ordering a generic belt. Clean off the old residue with IPA first โ€” new belts will not grip through it.
* '''Pinch roller (809162)''' โ€” hardens and develops flats with age. Symptom: tape speed drifts under load, or the tape edge curls because the roller no longer presses evenly.
* '''Head and capstan cleaning''' โ€” IPA on a foam swab, annually or every fifty tapes. Do not over-saturate: IPA running down the capstan washes old lubricant out of the bearing.
* There is '''no service-adjustable speed control'''. Amstrad's only speed instruction is a check, not an adjustment.


== Opening the System Unit ==
=== Azimuth adjustment ===


Tools: Philips #1 and #2 screwdriver, anti-static strap.
This is Amstrad's own procedure, and it is worth doing properly because a misaligned head is indistinguishable from a tired tape.<ref name="sm464" />


# Power off the system unit and unplug the DC power from the monitor.
Equipment: a test tape recorded with a '''constant 6 kHz tone''', and a valve/electronic voltmeter (Amstrad specifies a V.T.V.M.).
# Disconnect any joystick, printer or expansion-port peripherals.
# Place the keyboard face-down on a soft cloth.
# Remove all screws on the underside of the case. The number varies by revision (typically 6&ndash;8); some have additional screws beneath the model-name label.
# Carefully lift the lower half of the case. The cassette deck and main PCB remain attached to the upper half on most revisions.
# Disconnect the keyboard ribbon (or discrete wires on the original revision) from the main PCB at '''CP002'''. Note the orientation; on revisions with discrete wires, photograph the colour order before removing.
# Disconnect the cassette sub-PCB ribbon at '''CP001'''. The cassette sub-PCB carries IC301 (audio amp LA4140), IC302 (cassette read amp LA6324), the motor relay and the cassette head switches.


The volume potentiometer (VR301), the speaker and the cassette head connect to the cassette sub-PCB; the main PCB does '''not''' carry any of these. Both PCBs must be removed together if work on the cassette electronics is required.
# Set '''volume to maximum''' on the CPC464.
# Connect the meter to '''pin 7 of IC302''' (the LA6324 on the cassette PCB).
# Play the test tape and adjust the '''azimuth screw on the cassette head''' to read between '''330 mV and 520 mV'''.


== Regular Cleaning ==
=== Speed check ===


* Use a soft brush and low-pressure compressed air to clear dust from the main PCB, the keyboard mat and the cassette mechanism.
Put a standard tape in the mechanism and monitor the output on an oscilloscope, 100 ยตs range. Amstrad's tolerance statement is the useful part: '''a speed variation of ยฑ4% will not affect software loading.'''<ref name="sm464" /> If you are within that, the belt and pinch roller are not your fault.
* Avoid blowing dust into the cassette deck bearings or onto the keyboard contacts. Hold the cassette flywheel by hand if using compressed air near it.
* Clean the cassette R/P head, capstan and pinch roller with isopropyl alcohol on a foam swab. The R/P head is part 170201 in the IBM Amstrad service-spares catalogue. Foam swabs only &mdash; cotton fibres in the head gap are a known cause of intermittent reads.
* Clean the audio jack (J103), the 6-pin DIN video output (J101) and the joystick port (J102) with deoxidising contact cleaner sparingly on a foam swab.
* Clean the keyboard rubber-contact mats (parts 170008/170009/170010) by gently rolling them in a damp lint-free cloth. Do not use solvents on the silicone domes &mdash; they perish if exposed to acetone or IPA repeatedly.


== Keyboard Maintenance ==
=== Testing the cassette module on its own ===


The CPC 464 keyboard has a layered construction: '''hard plastic keytops''' (or flat keys on revisions 1+ where the keyboard ribbon connects through CP002), '''silicone rubber domes''' (parts 170008/170009/170010), and a flexible '''membrane contact PCB''' (parts 170028/170029).
The deck can be run independently of the CPU. Connect 5 V DC across points '''B(โˆ’)''' and '''C(+)''' on the cassette PCB and link '''E to G''' and '''H to F'''. The cassette will then operate in audio mode.<ref name="sm464" />


Common keyboard faults:
=== Amstrad's cassette fault chart ===


* '''Whole row dead''': membrane trace broken or contact PCB-to-main-PCB cable fault. Reseat the cable; if the row remains dead, check continuity along the membrane track for that row.
When tape loading fails, Amstrad's sequence is: '''check the connections to the tape deck โ†’ clean the tape head โ†’ check head alignment โ†’ check the switches on the cassette keys โ†’ check the tape motor control relay'''. If software loads but produces unusual results, the fault is on the computer board: RAM failure or ULA failure.<ref name="sm464" />
* '''Single key dead''': dirty contact. Open the keyboard, clean the relevant carbon pill on the silicone dome and the matching pad on the membrane with IPA on a swab. Do not abrade the carbon pill &mdash; it is conductive coating, not metal.
* '''Single key permanently active (stuck)''': membrane shorted, often by an old liquid spill that crystallised between two adjacent traces. Clean the trace area with IPA. If the short remains, isolate the trace by carefully scoring the membrane between the two adjacent pads &mdash; this is a last resort.
* '''Soft keys / no click''': silicone dome collapsed. Replace the dome from a donor keyboard; modern silicone replacement sets exist on the after-market.


The CPC 464 has no key matrix scan code reported in the BIOS to identify a stuck key (unlike a PC). The classic diagnostic is to type a known sequence at the BASIC prompt and look for additional characters appearing.
'''A useful thing that is not a fault:''' Amstrad states plainly that physical damage to a software tape stops it loading altogether โ€” "there will be no 'half' working programs. They either load โ€” or they don't."<ref name="sm464" />


== Cassette Deck Maintenance ==
== Power ==


The integrated cassette deck is a single-motor design driven by a rubber main belt (part 170204). The belt drives the flywheel (part 809156), which drives the capstan; a separate idler (part 809155) drives the take-up reel during play and rewind. Maintenance points:
The machine takes '''5 V DC''' on a DC jack socket, '''J104''', Amstrad part number '''170024'''. Amstrad's specification describes it as a "5 mm socket for CPC464 power supply (supplied exclusively from screen system)"; community documentation gives the mating plug as 2.1 mm.<ref name="sm464" /><ref name="grim464">[https://www.grimware.org/doku.php/documentations/hardware/amstrad.cpc464 "Amstrad CPC464"], Grimware โ€” hardware documentation for the CPC464 including the 5 V 2 A power requirement, the 2.1 mm DC plug, and the 50-way expansion connector pinout. Secondary source.</ref> The supply comes from the matching monitor, which contains a dedicated 5 V regulator stage for the computer.


* '''Main belt (170204)''': replaces about every 10&ndash;20 years; 35-year-old original belts are almost universally either liquefied (turned into a sticky black residue on the pulleys) or stretched. Symptom: tape will not load, motor runs but capstan does not turn. Replace the belt with a 67&times;1.2&nbsp;mm square-section drive belt of equal length.
If you intend to run the machine without an Amstrad monitor you need a stand-alone 5 V supply of adequate current. '''Check the polarity of your own board and your own plug before connecting anything''' โ€” the CPC464's power connector CP001 feeds +5 V and 0 V straight to the rails, and Amstrad's circuit diagram shows no reverse-polarity protection diode on that input.<ref name="sm464" />
* '''Pinch roller (809162)''': hardens with age. Symptom: tape speed drifts under load, or tape edge curls because the pinch roller is no longer compressing evenly. Replace with a modern silicone-rubber pinch-roller of matching diameter.
* '''Capstan and head cleaning''': clean every 50 tapes or annually, whichever comes first. IPA on a foam swab. Do not over-saturate &mdash; IPA running down the capstan can wash old lubricant out of the bearing.
* '''Speed adjustment''': the cassette motor (part 170208) has no service-adjustable speed pot; speed is set by the motor governor and the belt tension. A speed error of &plusmn;4% will not affect software loading per the official service manual; greater errors require pinch-roller and belt replacement before suspecting the motor.
* '''Azimuth''': adjusted by the screw on the R/P head. Insert a test tape recorded at 6 kHz constant tone, set volume to maximum, and adjust the azimuth screw to read 330&ndash;520 mV at pin 7 of IC302 (LA6324). This is per the official service-manual procedure.


The cassette sub-PCB carries two electrolytic capacitors that age (C322 470ยตF/10V on the motor relay, C315 100ยตF/16V on the audio output). See [[Amstrad CPC 464 Capacitor Replacement Guide]].
The first check on an unreliable machine โ€” random crashes, failure to start โ€” is '''5 V at J104''' with a meter, before suspecting anything on the board.


== Power Supply ==
== Connector care ==
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{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+'''CPC464 external connectors'''<ref name="sm464" />
! Ref !! Amstrad description !! Part no. !! Notes
|-
| '''J101''' || DIN socket, 6 pin || 170025 || RGB, sync, composite video and luminance+sync to the monitor. Bent pins are the common failure.
|-
| '''J102''' || Joystick socket, 9 pin || 170023 || Amstrad's pin names: 1 UP, 2 DOWN, 3 LEFT, 4 RIGHT, 5 SPARE, 6 FIRE 2, 7 FIRE 1, 8 COMMON, 9 COM 2<ref name="sm464" /><ref name="grim464" />
|-
| '''J103''' || Input/Output socket, 3.5 mm || 170022 || Stereo sound output. Line level โ€” not enough to drive headphones directly.
|-
| '''J104''' || DC jack socket || 170024 || 5 V in from the monitor
|-
| Printer port || PCB edge connector || โ€” || 34 physical contacts, but wired to '''36-pin Centronics numbering''' with pins 18 and 36 absent โ€” which is why Amstrad's own schematic labels it "36 way". Pin 9 is ground rather than D7, so the CPC has '''only 7 data bits'''; some printers need a converter.<ref name="cpcprn">[https://www.cpcwiki.eu/index.php/Connector:Printer_port "Connector: Printer port"], CPCWiki โ€” documents that the 34-pin edge connector uses 36-pin Centronics numbering with pins 18 and 36 absent, and that pin 9 is ground (or logic low on late cost-down models), giving 7 data bits. Secondary source.</ref>
|-
| Expansion port || PCB edge connector, 50 way || โ€” || '''Pin 1 = SOUND''' (from the AY-3-8912), '''pin 27 = +5 V''', '''pin 49 = GND''', '''pin 50 = CPUCLK''' (4 MHz). The connector for the DDI-1 disc interface, ROM boxes and other add-ons.<ref name="sm464" /><ref name="grim464" />
|}


The CPC 464 system unit takes '''5 V DC, 2 A''' on a 2.1 mm centre-positive jack at '''J104'''. This is normally supplied by the matching monitor: the CTM-640/CTM-644 colour monitors and the GT-64/GT-65 green monitors include a regulated 5 V supply specifically for the system unit. The DC cord is part 170316.
Clean edge fingers and the mating contacts with a soft eraser or contact cleaner. The CPC's edge fingers are exposed at the back of the case with no cover, so they oxidise faster than most contemporaries.


If the CPC 464 is to be used with a third-party display, a stand-alone 5 V DC supply of at least 2 A capacity with a centre-positive 2.1 mm DC plug is required. A 2.5 mm or 5.5 mm plug, or a polarity-reversed PSU, will not damage the system unit (the input is reverse-protected) but will not power it.
== Capacitor health ==


The original monitor PSUs and their 5 V regulator stages age; if the system unit shows random crashes or fails to start, verify '''5.0 V &plusmn;5%''' at J104 with a multimeter before suspecting the system unit.
The CPC464 carries '''thirteen aluminium electrolytics''' in total. '''Only two of them are on the main board''' โ€” C101 and C102, both 47 ยตF/10 V. The other eleven are all in the 300-series and live on the cassette PCB, including the largest, '''C322 (470 ยตF/10 V)'''.<ref name="sm464" /> Full values, circuit references and Amstrad part numbers: [[Amstrad CPC 464 Capacitor Replacement Guide]].


== Connector Care ==
The board also carries three '''polystyrene''' capacitors (C302, C305, C312). Polystyrene deforms at soldering temperatures an electrolytic shrugs off โ€” if you replace one, work fast and keep the iron off the body.


* '''J101''' (6-pin DIN female): RGB, sync, luminance, ground. Bent pins are a common DIN-socket failure mode. Inspect before reseating the monitor cable.
== ROM health ==
* '''J102''' (DB-9 male): joystick. Compatible with Atari-pin joysticks; the CPC adds Fire 3 on pin 5 (undocumented) and Joystick 2 ground on pin 9.
* '''J103''' (3.5 mm stereo jack): line-level audio output. Not strong enough to drive headphones directly &mdash; pass through an amplifier or low-impedance amplified speakers.
* '''J104''' (2.1 mm DC socket, centre positive): 5 V power input.
* '''Printer port''' (PCB edge connector, 34-pin): Centronics-compatible parallel printer port. The CPC has '''only 7 data bits''' (D7 is pulled to ground); some printers reject this and require a third-party 8-bit converter cable. Outputs are TTL-compatible.
* '''Expansion port''' (PCB edge connector, 50-pin): general-purpose system bus &mdash; the connector for the DDI-1 external floppy interface, the silicon disc, the multiface 2, ROM-boxes and aftermarket interfaces. Pin 1 carries the AY-3-8912 SOUND output, pins 27/49 carry +5 V and GND.


When reseating PCB edge connectors, clean the gold-plated fingers on the PCB and the contacts in the mating connector with a soft eraser or a deoxidising contact cleaner. Edge-connector contacts oxidise faster on the CPC 464 than on most contemporaries because the PCB-edge fingers are exposed at the rear of the case.
The operating system and Locomotive BASIC 1.0 live in a single 32 KB mask ROM at '''IC103''', marked '''TMM-23256P-1950''', Amstrad service part '''170102'''.<ref name="sm464" /> The corresponding Amstrad custom-chip number is '''40009''' for the English-language firmware; '''40037''' is Spanish and '''40050''' French.<ref name="cpcparts">[https://www.cpcwiki.eu/index.php/Amstrad_part_numbers "Amstrad part numbers"], CPCWiki โ€” catalogue of Amstrad 40xxx custom-chip numbers, including 40009 (CPC464 English firmware), 40037 (Spanish), 40050 (French), 40022 (CPC664 firmware) and 40015 (AMSDOS). Secondary source.</ref>


== Capacitor Health ==
Mask ROM has no UV-degradation path and does not fail with age. The common ROM-related fault is a bad socket contact, not a bad chip. If the machine boots to corrupted characters or hangs at the prompt, reseat IC103 before suspecting it.


Most CPC 464 capacitor faults do not cause symptoms while the system is unpowered, but they accumulate as the system ages: the 470 ยตF/10 V electrolytic on the cassette motor relay (C322 on the cassette sub-PCB) is the most common to fail. Aluminium electrolytic capacitors throughout the system are now 35+ years old and at the point where pre-emptive replacement is reasonable. Full procedure and parts list: [[Amstrad CPC 464 Capacitor Replacement Guide]].
== Recommended tools ==


== ROM Health ==
* Philips screwdrivers and an anti-static strap.
* Digital multimeter โ€” the single most useful tool on this machine, because so many faults resolve to 5 V not arriving.
* IPA and '''foam''' swabs for the cassette head and capstan.
* Oscilloscope and an electronic voltmeter, if you intend to do the azimuth and speed checks properly.
* A 6 kHz constant-tone test tape.
* Replacement main belt โ€” measure your own pulleys; Amstrad publishes only the part number (170204).
* Fine-tip soldering iron and solder wick for capacitor work.
* A stand-alone 5 V supply, if you want to test the computer without its monitor.
* See [[Recommended Tools]] for the general workshop kit.


The CPC 464 holds its operating system (Amstrad Firmware v1.0, part 40009) and Locomotive BASIC 1.0 in a single 32 KB mask ROM at IC103 (TMM-23256P-1950). Mask ROM is more robust than EPROM: there is no UV-degradation path. The most common ROM-related fault is a bad socket, not a bad chip. Reseat IC103 if the system boots to a corrupted character pattern or hangs at the prompt.
== Technical specification ==


The English-language firmware part number is '''40009'''; Spanish firmware is '''40037'''; French firmware is '''40050''' (paired with an AZERTY keyboard mat).
From Amstrad's own specification page.<ref name="sm464" />


== Recommended Tools ==
{| class="wikitable styled-table" style="width:85%; text-align:left;"
|+'''CPC464 โ€” Amstrad's published specification'''<ref name="sm464" />
! Item !! Figure
|-
| Processor || Z80A at 4 MHz
|-
| RAM / ROM || 64 KB RAM (over 42 KB available to the user) / 32 KB ROM
|-
| Video / sound / I/O || 6845 CRT controller ยท AY-3-8912 (3 voice, 7 octave) ยท 8255 parallel I/O
|-
| Keyboard || 74 keys
|-
| Keyboard unit || 580 ร— 70 ร— 170 mm, 2.4 kg
|-
| CTM640 monitor || 375 ร— 340 ร— 365 mm, 10.6 kg
|-
| GT64 monitor || 305 ร— 315 ร— 335 mm, 6.3 kg
|-
| Mains || 240 V AC 50 Hz โ€” '''at the monitor'''; keyboard and datacorder are powered from the screen system
|}


* Philips #1 and #2 screwdrivers.
'''There is no cooling fan.''' No fan or fan motor appears anywhere in Amstrad's parts lists, and the machine is passively cooled.<ref name="sm464" />
* Anti-static strap.
* Digital multimeter.
* IPA + foam swabs for the cassette head and capstan.
* Soft brush + compressed air.
* 67&times;1.2 mm square-section drive belt for the cassette mechanism.
* Modern silicone replacement pinch roller (matching the OEM 13 mm pinch roller).
* Soldering iron with fine tip + solder wick for capacitor work.
* Replacement 5 V / 2 A centre-positive PSU (optional, for use without an Amstrad monitor).
* DDI-1 / DDI-3 / equivalent disk interface, if disk operation is required.


== Related Pages ==
== Related pages ==


* [[Amstrad CPC 464]]
* [[Amstrad CPC 464]] ยท [[Amstrad CPC 464 Troubleshooting Guide]] ยท [[Amstrad CPC 464 Capacitor Replacement Guide]]
* [[Amstrad CPC 464 Troubleshooting Guide]]
* '''[[Amstrad CPC 464 Service Manual]]''' โ€” the source for the part numbers, alignment figures and fault charts on this page
* [[Amstrad CPC 464 Capacitor Replacement Guide]]
* [[Amstrad CPC 664]] โ€” the successor, with a built-in 3-inch disc drive
* [[Amstrad CPC 664]] &mdash; successor with built-in 3" floppy drive
* [[Amstrad DDI-1 / FD-1 Service Manual]] โ€” the external 3-inch disc option for the 464
* Amstrad CPC 6128 &mdash; 128 KB successor
* [[CRT Discharge Procedure]] ยท [[Capacitor Failure Symptoms]] ยท [[Recommended Tools]]
* [[Recommended Tools]]


== References ==
== References ==


* [https://archive.org/details/Amstrad_CPC464_Service_Manual_1985_Amstrad_Consumer_Electronics Amstrad CPC464 Service Manual] (1985, Amstrad Consumer Electronics). Source for the cabinet parts list (170001&ndash;170124), cassette mechanism parts list (170201&ndash;170212 + 809155&ndash;809175), cassette deck alignment procedure (azimuth at IC302 pin 7), electrical parts list with full IC numbering (IC101&ndash;IC125 main board, IC301&ndash;IC302 cassette), and the main PCB layout.
<references />
* [https://www.grimware.org/doku.php/documentations/hardware/amstrad.cpc464 Amstrad CPC 464 hardware documentation], Grimware. Source for the four motherboard revisions (Z70100, Z70200, Z70373, 28032?), Gate Array variants (40007 / 40010 / 40226 cost-down ASIC), connector pinouts, and dimensions.
* [https://cpctech.cpcwiki.de/docs/cpcrev.html CPC hardware revisions], CPCWiki / cpctech.org.uk. Per-revision IC list for the CPC 464.


{{Navbox-Amstrad|state=collapsed}}
{{Navbox-Amstrad|state=collapsed}}

Latest revision as of 11:05, 27 September 2026

CPC 464 with the CTM640 colour monitor. The monitor contains the computer's only power supply โ€” and the only mains voltage in the system.

Preventive maintenance for the Amstrad CPC 464 (1984), covering the main PCB, the cassette sub-PCB and deck, the keyboard, the monitor that supplies the machine's power, and the connectors. Fault diagnosis is in the Amstrad CPC 464 Troubleshooting Guide; component values are in the Amstrad CPC 464 Capacitor Replacement Guide.

Part numbers, circuit references and alignment figures on this page are Amstrad's own, from the Amstrad CPC 464 Service Manual hosted on this wiki.[1]

The monitor is the power supply

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The CPC 464 has no mains connection and no internal power supply. The machine takes 5 V DC through a DC socket on the back, and Amstrad's own specification states that this is "supplied exclusively from screen system" โ€” the CTM640 colour monitor or the GT64 green monitor.[1] Mains enters the monitor, not the computer.

That changes how you approach a dead machine, and it changes the hazards:

  • The computer itself is safe to open. There is no mains voltage anywhere inside the keyboard unit. You can work on the main PCB, the cassette PCB and the keyboard with the DC lead disconnected and nothing worse than static to worry about.
  • The monitor is not. The CTM640 and GT64 contain a CRT with a lethal anode charge and mains-derived bulk capacitors that hold charge after switch-off. Read CRT Discharge Procedure before opening either.
  • A "dead CPC" is very often a dead monitor. Amstrad's own fault-finding chart sends you to the monitor's 5 V supply and the DC cord before anything on the computer board.[1]

Amstrad's safety-test specification for the monitors, for reference: a flash test at 4 kV between the mains lead (live and neutral joined) and all accessible exterior metal, and an insulation-resistance test on the same points showing at least 4 Mฮฉ.[1]

Identifying your board

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The CPC 464 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.[2]

Amstrad CPC 464 main PCB versions[2]
Version Silkscreen Size Notes
v1 (ยฉ1983) Z70100 (no MC code), 270100 MC0001A, or Z70100 MC0001A 405 ร— 155 mm Gate Array with a cooling plate; VCC2 fed through R138/R139
v2 (ยฉ1984) Z70200 with MC0001A, MC0002A/B/C/D, MC0003A, MC0008B/C/D 405 ร— 152 mm Separate solder pads for both the old and the new Gate Array; 6128-style 2 ร— 10-pin dual-foil keyboard connector
v3 Z70374 MC0044A, Z70374 MC0044B, Z70375 MC0044D, Z70378 MC0046A 240 ร— 150 / 238 ร— 145 mm Same parts packed tighter; joystick and stereo sockets moved to the left side
v4 "cost-down" (ยฉ1988) Z80329 MC0099A 237 ร— 108 mm 100-pin SMD ASIC (part 40226) combining the Gate Array, CRTC and some FDC, DRAM and reset logic

On the original board Amstrad's own parts list gives the Gate Array as IC116, marked 20RA043, Amstrad part number 40007.[1]

Opening the unit

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Tools: a Philips screwdriver and an anti-static strap.

  1. Switch off and unplug the DC lead from the monitor.
  2. Disconnect any joystick, printer or expansion-port peripheral.
  3. Lay the keyboard face-down on a soft cloth and remove the underside screws. The count varies by board version; some are hidden under the model-name label.
  4. Lift the lower half of the case.
  5. Disconnect the keyboard cable. On v1 boards this is discrete wiring โ€” photograph the colour order before you unplug anything. From v2 onward it is a 2 ร— 10-pin dual-foil connector.[2]
  6. Disconnect the cassette PCB at CD001, the 8-way connector on the cassette board. Amstrad labels the conductors on the PCB layout: 1 INPUT, 2 PLAY ON (yellow), 3 SOUND IN (white), 4 DATA OUT (green), 5 DATA IN (blue), 6 GND (black), 7 +B (white), 8 +B (red).[1]

Almost all the analogue electronics are on the cassette PCB, not the main board. It carries IC301 (LA4140 audio power amplifier), IC302 (LA6324 quad op-amp for the cassette read chain), VR301 (the 20 kฮฉ volume control), RY301 (the tape motor relay), SP301 (the speaker), L301, D301, D302 (the red power LED, SLP-145B) and the whole 300-series resistor and capacitor population.[1] If you are chasing an audio or tape fault, that is the board you want.

Regular cleaning

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  • Soft brush and low-pressure air for the main PCB, the keyboard mat and the cassette mechanism. Hold the cassette flywheel by hand if you use air near it.
  • Clean the R/P head (Amstrad part 170201), capstan and pinch roller with IPA on a foam swab. Cotton fibres left in the head gap are a known cause of intermittent reads.
  • Clean the connectors โ€” the 6-pin DIN video socket J101, the 9-pin D joystick socket J102, the 3.5 mm socket J103 and the DC socket J104 โ€” with contact cleaner sparingly on a foam swab.[1]
  • Clean the keyboard rubber contact mats (Amstrad parts 170008 key board mat, 170009 digit mat, 170010 spacer) by rolling them gently in a damp lint-free cloth. Do not soak the silicone in solvents.

Keyboard maintenance

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The CPC 464 keyboard is a 74-key assembly in QWERTY layout with a numeric cluster, cursor and copy cursor, large enter, shift, caps lock, tab, escape, delete, clear and control.[1] It is built up from keytops, silicone rubber contact mats (170008/170009/170010) and a flexible contact PCB in two halves (Amstrad parts 170028 and 170029).[1]

Common faults:

  • A whole row dead โ€” a broken membrane trace, or a fault in the cable between the contact PCB and the main board. Reseat the cable first, then check continuity along the row's track.
  • A single key dead โ€” dirty contact. Clean the carbon pill on the silicone dome and its matching pad on the membrane with IPA on a swab. Do not abrade the pill โ€” it is a conductive coating, not metal, and rubbing it off is permanent.
  • A single key permanently active โ€” a short on the membrane, usually an old liquid spill that crystallised between adjacent traces. Clean the area with IPA. Scoring the membrane between the pads to isolate the trace is a last resort.
  • Soft keys, no click โ€” a collapsed silicone dome. Replace from a donor mat.

Amstrad's own fault chart for "do all keys operate?" sends you to inspect the keyboard PCB for cracks, liquid spillage and distorted mounting, then to check the connector lead and its termination.[1]

Cassette deck maintenance

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The deck is a single-motor mechanism. Amstrad's parts list gives every wear item a number:[1]

CPC464 cassette mechanism โ€” service-relevant parts[1]
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 170014
Cassette Mechanism (complete) 170012
  • Main belt (170204) โ€” the usual failure. Thirty-plus-year-old originals are almost universally either liquefied into a sticky black residue on the pulleys or stretched beyond useful tension. Symptom: the motor runs but the capstan does not turn, and tapes will not load. Amstrad publishes no replacement dimensions, only the part number, so measure your own pulleys before ordering a generic belt. Clean off the old residue with IPA first โ€” new belts will not grip through it.
  • Pinch roller (809162) โ€” hardens and develops flats with age. Symptom: tape speed drifts under load, or the tape edge curls because the roller no longer presses evenly.
  • Head and capstan cleaning โ€” IPA on a foam swab, annually or every fifty tapes. Do not over-saturate: IPA running down the capstan washes old lubricant out of the bearing.
  • There is no service-adjustable speed control. Amstrad's only speed instruction is a check, not an adjustment.

Azimuth adjustment

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This is Amstrad's own procedure, and it is worth doing properly because a misaligned head is indistinguishable from a tired tape.[1]

Equipment: a test tape recorded with a constant 6 kHz tone, and a valve/electronic voltmeter (Amstrad specifies a V.T.V.M.).

  1. Set volume to maximum on the CPC464.
  2. Connect the meter to pin 7 of IC302 (the LA6324 on the cassette PCB).
  3. Play the test tape and adjust the azimuth screw on the cassette head to read between 330 mV and 520 mV.

Speed check

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Put a standard tape in the mechanism and monitor the output on an oscilloscope, 100 ยตs range. Amstrad's tolerance statement is the useful part: a speed variation of ยฑ4% will not affect software loading.[1] If you are within that, the belt and pinch roller are not your fault.

Testing the cassette module on its own

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The deck can be run independently of the CPU. Connect 5 V DC across points B(โˆ’) and C(+) on the cassette PCB and link E to G and H to F. The cassette will then operate in audio mode.[1]

Amstrad's cassette fault chart

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When tape loading fails, Amstrad's sequence is: check the connections to the tape deck โ†’ clean the tape head โ†’ check head alignment โ†’ check the switches on the cassette keys โ†’ check the tape motor control relay. If software loads but produces unusual results, the fault is on the computer board: RAM failure or ULA failure.[1]

A useful thing that is not a fault: Amstrad states plainly that physical damage to a software tape stops it loading altogether โ€” "there will be no 'half' working programs. They either load โ€” or they don't."[1]

Power

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The machine takes 5 V DC on a DC jack socket, J104, Amstrad part number 170024. Amstrad's specification describes it as a "5 mm socket for CPC464 power supply (supplied exclusively from screen system)"; community documentation gives the mating plug as 2.1 mm.[1][3] The supply comes from the matching monitor, which contains a dedicated 5 V regulator stage for the computer.

If you intend to run the machine without an Amstrad monitor you need a stand-alone 5 V supply of adequate current. Check the polarity of your own board and your own plug before connecting anything โ€” the CPC464's power connector CP001 feeds +5 V and 0 V straight to the rails, and Amstrad's circuit diagram shows no reverse-polarity protection diode on that input.[1]

The first check on an unreliable machine โ€” random crashes, failure to start โ€” is 5 V at J104 with a meter, before suspecting anything on the board.

Connector care

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CPC464 external connectors[1]
Ref Amstrad description Part no. Notes
J101 DIN socket, 6 pin 170025 RGB, sync, composite video and luminance+sync to the monitor. Bent pins are the common failure.
J102 Joystick socket, 9 pin 170023 Amstrad's pin names: 1 UP, 2 DOWN, 3 LEFT, 4 RIGHT, 5 SPARE, 6 FIRE 2, 7 FIRE 1, 8 COMMON, 9 COM 2[1][3]
J103 Input/Output socket, 3.5 mm 170022 Stereo sound output. Line level โ€” not enough to drive headphones directly.
J104 DC jack socket 170024 5 V in from the monitor
Printer port PCB edge connector โ€” 34 physical contacts, but wired to 36-pin Centronics numbering with pins 18 and 36 absent โ€” which is why Amstrad's own schematic labels it "36 way". Pin 9 is ground rather than D7, so the CPC has only 7 data bits; some printers need a converter.[4]
Expansion port PCB edge connector, 50 way โ€” Pin 1 = SOUND (from the AY-3-8912), pin 27 = +5 V, pin 49 = GND, pin 50 = CPUCLK (4 MHz). The connector for the DDI-1 disc interface, ROM boxes and other add-ons.[1][3]

Clean edge fingers and the mating contacts with a soft eraser or contact cleaner. The CPC's edge fingers are exposed at the back of the case with no cover, so they oxidise faster than most contemporaries.

Capacitor health

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The CPC464 carries thirteen aluminium electrolytics in total. Only two of them are on the main board โ€” C101 and C102, both 47 ยตF/10 V. The other eleven are all in the 300-series and live on the cassette PCB, including the largest, C322 (470 ยตF/10 V).[1] Full values, circuit references and Amstrad part numbers: Amstrad CPC 464 Capacitor Replacement Guide.

The board also carries three polystyrene capacitors (C302, C305, C312). Polystyrene deforms at soldering temperatures an electrolytic shrugs off โ€” if you replace one, work fast and keep the iron off the body.

ROM health

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The operating system and Locomotive BASIC 1.0 live in a single 32 KB mask ROM at IC103, marked TMM-23256P-1950, Amstrad service part 170102.[1] The corresponding Amstrad custom-chip number is 40009 for the English-language firmware; 40037 is Spanish and 40050 French.[5]

Mask ROM has no UV-degradation path and does not fail with age. The common ROM-related fault is a bad socket contact, not a bad chip. If the machine boots to corrupted characters or hangs at the prompt, reseat IC103 before suspecting it.

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  • Philips screwdrivers and an anti-static strap.
  • Digital multimeter โ€” the single most useful tool on this machine, because so many faults resolve to 5 V not arriving.
  • IPA and foam swabs for the cassette head and capstan.
  • Oscilloscope and an electronic voltmeter, if you intend to do the azimuth and speed checks properly.
  • A 6 kHz constant-tone test tape.
  • Replacement main belt โ€” measure your own pulleys; Amstrad publishes only the part number (170204).
  • Fine-tip soldering iron and solder wick for capacitor work.
  • A stand-alone 5 V supply, if you want to test the computer without its monitor.
  • See Recommended Tools for the general workshop kit.

Technical specification

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From Amstrad's own specification page.[1]

CPC464 โ€” Amstrad's published specification[1]
Item Figure
Processor Z80A at 4 MHz
RAM / ROM 64 KB RAM (over 42 KB available to the user) / 32 KB ROM
Video / sound / I/O 6845 CRT controller ยท AY-3-8912 (3 voice, 7 octave) ยท 8255 parallel I/O
Keyboard 74 keys
Keyboard unit 580 ร— 70 ร— 170 mm, 2.4 kg
CTM640 monitor 375 ร— 340 ร— 365 mm, 10.6 kg
GT64 monitor 305 ร— 315 ร— 335 mm, 6.3 kg
Mains 240 V AC 50 Hz โ€” at the monitor; keyboard and datacorder are powered from the screen system

There is no cooling fan. No fan or fan motor appears anywhere in Amstrad's parts lists, and the machine is passively cooled.[1]

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References

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  1. โ†‘ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 Amstrad Consumer Electronics plc, CPC464 Micro Computer / CTM640 Colour Monitor / GT64 Green Monitor Service Manual. Hosted at Amstrad CPC 464 Service Manual. Source for the technical specification (page 2), the CPC464 Cabinet Parts List (page 2), the Cassette Mechanism Parts List and Cassette Deck Alignment Instructions (page 6), the Cassette PCB layout (page 7), the Basic Hardware Analysis flow chart (page 9), the Cassette & Software Analysis chart (page 10) and the CPC464 Electrical Parts List (page 17).
  2. โ†‘ 2.0 2.1 2.2 "Mainboard Versions", CPCWiki. Community catalogue of silkscreen markings, board dimensions, copyright dates and per-version changes for the CPC 464, 664 and 6128 main boards. Secondary source, compiled from observed boards.
  3. โ†‘ 3.0 3.1 3.2 "Amstrad CPC464", Grimware โ€” hardware documentation for the CPC464 including the 5 V 2 A power requirement, the 2.1 mm DC plug, and the 50-way expansion connector pinout. Secondary source.
  4. โ†‘ "Connector: Printer port", CPCWiki โ€” documents that the 34-pin edge connector uses 36-pin Centronics numbering with pins 18 and 36 absent, and that pin 9 is ground (or logic low on late cost-down models), giving 7 data bits. Secondary source.
  5. โ†‘ "Amstrad part numbers", CPCWiki โ€” catalogue of Amstrad 40xxx custom-chip numbers, including 40009 (CPC464 English firmware), 40037 (Spanish), 40050 (French), 40022 (CPC664 firmware) and 40015 (AMSDOS). Secondary source.


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