Amstrad CPC 664 Maintenance Guide

CPC 664 with its colour monitor. The monitor supplies both the computer's 5 V and the disc drive's 12 V, on two separate leads.

Preventive maintenance for the Amstrad CPC 664 (1985), concentrating on the built-in 3-inch disc drive, which is what makes the 664 different from the CPC 464. Fault diagnosis is in the Amstrad CPC 664 Troubleshooting Guide; component values are in the Amstrad CPC 664 Capacitor Replacement Guide.

The 664 had an unusually short life. It was on sale from May to August 1985 before the 6128 replaced it, which is why it is scarcer than either the 464 or the 6128, and why the community knowledge base around it is thinner. The keyboard, audio chain and most of the main board are shared with the 464, so the CPC 464 maintenance procedures apply to everything outside the disc subsystem.

Part numbers, circuit references and alignment figures here are Amstrad's own, from the Amstrad CPC 664 Service Manual hosted on this wiki.

The monitor is the power supply

Like the 464, the CPC 664 has no mains connection and no internal power supply. Amstrad's specification lists two separate DC connections on the back of the machine: a 5 mm socket for the CPC664 5 V supply from the monitor, and a 5 mm plug and lead that goes out to the 12 V (disc) power socket on the monitor. The CTM644 colour monitor and GT65 green monitor provide both.

In the parts list these are J301 (DC jack, Amstrad part 170024 — the same part as the 464's J104) and CD301 (DC cord, part 170822). There is no five-pin DIN power connector on this machine; the 5-pin DIN on the back (J302, part 170819) is the external cassette recorder socket, and the 3.5 mm socket (J103) is stereo audio out.

Consequences for servicing:

• The computer is safe to open. No mains inside the keyboard unit.
• The monitor is not. CRT anode charge and mains-derived bulk capacitors persist after switch-off — see CRT Discharge Procedure.
• A drive that will not spin is very often a 12 V problem, not a drive problem. The 12 V comes down a separate lead from the monitor, and that lead is a single point of failure. Check it before opening the drive.

Identifying your board

The CPC 664 main board is Z70205, 475 × 155 mm, in two variants:

Amstrad CPC 664 main PCB variants

Silkscreen	Notes
Z70205 MC0005A	8-pin FDC data separator
Z70205 MC0005B	German Schneider boards. Usually carries a patch resistor R160 between pin 9 (A0) and pin 14 (/CASADDR) of IC105, which is not labelled on the PCB — do not mistake it for a previous owner's bodge

Z70200 is a CPC 464 board, not a 664 board. If your board is marked Z70200 you are looking at a 464.

Amstrad's parts list gives the key devices:

CPC664 — principal devices

Ref	Device	Amstrad part no.	Role
IC103	TMM-23256P-1952	40022	32 KB OS + Locomotive BASIC 1.1 ROM
IC204	TMM-23128P-1951	40015	16 KB AMSDOS ROM
IC111	Z8400APS	40080	Z80A CPU
IC116	HSG3130 / HSG3170	40010	Gate Array
IC108	HD6845SP	170106	CRTC
IC107	M5L8255AP-5	170105	Parallel I/O
IC102	AY-3-8912	40001	Sound generator
IC117–IC124	HM4864U-2	170110	64 KB DRAM, eight 64K × 1 devices
IC201	µPD765AC	40018	Floppy disc controller
IC202	FDC9216BT	40020	Data separator
IC301	LA4140	170111	Audio power amplifier
IC302	LA63585	170814	Cassette read chain

Opening the unit

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

1. Switch off and disconnect both DC leads from the monitor — the 5 V feed and the 12 V lead.
2. Disconnect joystick, printer and expansion-port peripherals.
3. Lay the keyboard face-down on a soft cloth and remove the underside screws.
4. Lift the case halves apart carefully; take photographs as you go rather than relying on memory.
5. Disconnect the disc drive cable. Amstrad's parts list calls the drive lead CD201 (part 170821). Note pin 1 orientation before unplugging.
6. Disconnect the keyboard cable.

The 664 keeps the cassette interface even though it has no cassette deck. IC301 (LA4140), IC302 (LA63585), the tape motor relay RY301, the speaker SP301, the volume control and the whole 300-series component population are all present, feeding the 5-pin DIN socket J302 for an external recorder. If you have read elsewhere that the 300-series capacitors are absent on a 664, that is wrong — Amstrad's own parts list has C301, C303, C304, C306, C308, C309, C311, C314, C315, C316 and C317 all fitted.

The disc drive

What is actually fitted

Amstrad's specification describes the drive as "a 3" system, conforming to the Hitachi/Panasonic standard", software-configured for a 12 ms step rate and 30 ms settling time. The mechanism fitted is from the Matsushita EME series — the CPC664 and the early DDI-1 and CPC6128 used the EME-150A on PCB 30001, which is the PCB number Amstrad's own service manual refers to throughout. Later machines in the family used the EME-155, EME-156 and EME-156V. All are single-sided, 40 track, 180 KB per side, 300 rpm, and all except the late EME-157 need both 5 V and 12 V.

The FD-1 is the second-drive add-on for the 664, using the same mechanism family. A 3-inch disc is double-sided in the physical sense — both surfaces are usable, and each side has its own reusable write-protect clip — but the drive only reads the side facing it, so you flip the disc by hand.

Amstrad's own position on the mechanism

Printed twice in the manual, in a box: "Service Agents must not carry out any repair or adjustment to the Drive mechanism and its associated PCB 30001 during warranty. Faulty mechanism must be returned to AMSTRAD for exchange." That was Amstrad's commercial policy in 1985, not a statement that the drive is unserviceable. It does mean the manual gives no component values for the drive PCB — the parts list carries the matching note that no part numbers are given for any part on that PCB. What it does give is the mechanical parts breakdown, the alignment checks and the replacement procedures below, all of which remain usable.

Mechanism parts

Amstrad's exploded view numbers the following:

CPC664 3-inch drive mechanism

No.	Part
1	Head Assembly
2	Stepper Motor
3	Stepper Motor Rotation Bolt
4	Spindle Motor
5	Flywheel
6	Pulley
7	Read/Write Protect / Index / LED P.C.B.
8	Track 00 Sensor Assembly
9	Spring
10	Loading Unit

The drive belt runs on the underside of the loading unit, from the pulley (6) on the spindle motor to the flywheel (5).

Drive belt

The perished belt is the characteristic 664 fault. After thirty-odd years the original is usually either liquefied into black gum on both pulleys or stretched past useful tension. Symptom: the motor runs, the disc does not spin, and the machine reports a read failure on a known-good disc.

Amstrad publishes no belt dimensions. The community specification for the CPC664 / 6128 / FD-1 3-inch drive belt is 3 mm wide, 0.6 mm thick, 230 mm outer circumference — often advertised as "115 mm", which is the flat length. Measure your own pulleys before ordering.

Procedure, following Amstrad's own spindle-motor sequence:

1. Remove the drive from the case and take off the top cover.
2. If the old belt has liquefied, clean both pulleys thoroughly with IPA. New belts will not grip through the residue.
3. Fit the new belt over pulley and flywheel, and turn it by hand to confirm it sits centred and does not slip.
4. Check the index period afterwards. Amstrad's spindle-motor procedure ends with "adjust VR201 so index frequency is 200 ± 2 ms" — see below.

Spindle speed — VR201

This is the single most useful thing in the 664 manual and it is widely missed: the spindle speed is adjustable, on the drive's own control PCB, at VR201.

• Target: index period 200 ± 1 ms in the diagnostic flow chart, 200 ± 2 ms in the spindle-motor replacement procedure. 200 ms is one revolution at 300 rpm.
• If the motor rotates but the period is out and VR201 will not bring it in, Amstrad's chart sends you to substitute a known-good motor: if the drive then runs correctly, replace the motor; if not, replace the drive.
• If the motor does not rotate at all, check that power is arriving before anything else.

Set the speed after any belt change. A belt that grips but runs slow decodes as read errors, not as a mechanical fault.

Stepper and head

• The head carriage runs on a rod, moved by the stepper through a lead screw. Amstrad's head-replacement procedure involves removing the control PCB, unplugging the stepper and LED PCB, freeing the loading unit, then sliding the head off the rod — and it ends with "check alignment of Azimuth Burst / Track 00 Positioning". Do not take the head off casually.
• After replacing the stepper motor, index and positioning must be checked and amended as necessary.
• The Track 00 sensor assembly (8) is an optical part. Dust in it produces a track-0 fault that looks like a stepper failure.

Alignment checks

Amstrad gives a real alignment procedure. Equipment: a double-beam oscilloscope and the EME-CF2 test disk.

Amstrad's alignment checks

Check	Track used
Radial adjustment	Track 19
Adjustment of the index burst	Track 39
Azimuth check	Track 39

Drive test points

TP	Signal
TP1, TP2	Read signal of filter outlet
TP3, TP11	Signal ground
TP5	Track 00 sensor output
TP9	Index signal

Amstrad's framing is worth repeating: "If the wave patterns do not appear this confirms a fault with the mechanism. Before attempting any replacement check these waveforms thoroughly."

In practice, for a machine you are restoring rather than servicing under warranty: alignment rarely drifts on its own. If the drive reads commercial discs but not discs you wrote on another machine, the other machine is the misaligned one. Work through belt, speed, head cleanliness and the Track 00 sensor before suspecting alignment.

Head cleaning

IPA on a foam swab. Do not use cotton — fibres in the head gap cause CRC errors and intermittent reads. Amstrad's note in the error section is blunt: "Always ensure the head is clean."

AMSDOS ROM

AMSDOS lives in a separate 16 KB ROM at IC204 (TMM-23128P-1951, Amstrad part 40015), alongside the 32 KB OS+BASIC ROM at IC103 (part 40022).

• Socket contact failure is the common AMSDOS fault, not chip failure. Mask ROMs do not degrade. Reseat before suspecting anything.
• Unexpected disc behaviour is almost never the ROM. Check the disc, the drive cable and the mechanism first.
• Community-developed replacements (ROMDOS, PARADOS) fit the same socket and add features such as larger formats and faster access.

Capacitor health

The CPC664 carries twelve aluminium electrolytics across five values, and five polystyrene capacitors. Values, circuit references and Amstrad part numbers: Amstrad CPC 664 Capacitor Replacement Guide.

Note two things:

• The 664's ceramic decoupling runs C101–C128 and C201–C213 — the 200-series is the disc interface section, which the 464 does not have.
• Amstrad gives no values for anything on the drive's own PCB 30001. Anything you read elsewhere claiming specific capacitor values for the 664's drive board did not come from Amstrad. Read them off your own board.

The polystyrene capacitors (C302, C305, C312, C318, C319) deform at soldering temperatures an electrolytic tolerates easily. Work quickly and keep the iron off the body.

Regular cleaning

• Soft brush and low-pressure air for the main PCB, the disc-controller area and the keyboard mat.
• Clean the drive head with IPA on a foam swab.
• Clean the 6-pin DIN video socket, the 9-pin D joystick socket, the 3.5 mm audio socket, the 5-pin DIN cassette socket and the printer and expansion edge connectors with contact cleaner sparingly on a foam swab.
• Keyboard rubber mats and contact PCB: identical to the 464, and the Amstrad CPC 464 Maintenance Guide procedure applies unchanged.

Recommended tools

• Philips screwdrivers and an anti-static strap.
• Digital multimeter — the 12 V disc feed is the first thing to check on a non-spinning drive.
• Oscilloscope, ideally double-beam, if you intend to use Amstrad's alignment checks.
• IPA and foam swabs.
• Replacement drive belt — measure your own pulleys; the community figure is 3 mm × 0.6 mm × 230 mm.
• Small trim tool for VR201.
• A known-good 3-inch disc for testing.
• Fine-tip soldering iron and solder wick for capacitor work.
• A Gotek with FlashFloppy, or an HxC, if the original mechanism is beyond economic repair.
• See Recommended Tools and Floppy Drive Repair.

Technical specification

From Amstrad's own specification page.

CPC664 — Amstrad's published specification

Item	Figure
Processor	Z80A at 4 MHz
RAM / ROM	64 KB RAM (over 41 KB available to the user) / 32 KB ROM for BASIC and OS
Video / sound / I/O	6845 CRT controller · AY-3-8912 (3 voice, 8 octave) · 8255 parallel I/O
Keyboard	74 keys
Disc drive	3 inch, 12 ms step rate, 30 ms settling time, maximum 2 drives
Disc formats	Single sided, double density, 512-byte sectors, 40 tracks, 2:1 interleave. SYSTEM 9 sectors/track, 2 reserved tracks, 169 KB · DATA 9 sectors/track, no reserved tracks, 178 KB · IBM 8 sectors/track, 1 reserved track, 154 KB
Expansion	Up to 252 additional 16 KB ROMs
Keyboard unit	580 × 70 × 170 mm, 2.4 kg
CTM644 monitor	375 × 340 × 365 mm, 10.6 kg
GT65 monitor	305 × 315 × 335 mm, 6.3 kg
Mains	240 V AC 50 Hz — at the monitor; keyboard and disc drive power both come from the screen system

Related pages

• Amstrad CPC 664 · Amstrad CPC 664 Troubleshooting Guide · Amstrad CPC 664 Capacitor Replacement Guide
• Amstrad CPC 664 Service Manual — the source for the part numbers, alignment figures and procedures on this page
• Amstrad CPC 464 Maintenance Guide — the keyboard, audio and cleaning sections apply unchanged to the 664
• Amstrad DDI-1 / FD-1 Service Manual — the same 3-inch drive family, as the external unit
• Floppy Drive Repair · CRT Discharge Procedure · Capacitor Failure Symptoms · Recommended Tools