Editing Amstrad CPC 664 Maintenance Guide

This guide documents preventive maintenance procedures for the '''[[Amstrad CPC 664]]''' (1985, Amstrad part number Z70200 / MC0030 family). The 664 inherits the keyboard, main PCB layout and audio chain of the [[Amstrad CPC 464|CPC 464]] and adds an integrated '''Hitachi-mechanism 3-inch floppy drive''' with a NEC uPD765A FDC and a 16 KB AMSDOS ROM. Almost all of the [[Amstrad CPC 464 Maintenance Guide|CPC 464 maintenance procedures]] apply equally to the 664; this guide concentrates on the floppy-drive maintenance, drive belt replacement, head alignment and AMSDOS ROM care that are specific to the 664 / 6128 family.

== Safety Warning ==

Same as the CPC 464: the '''system unit''' itself runs on regulated 5 V DC (and +12 V on the 664 for the drive motor) supplied by the matching monitor. There is no mains voltage inside the system unit; capacitor work on the main PCB and the disc-controller area is low-risk.

The '''CTM-644 / GT-64 / GT-65 monitor''' contains the CRT (15&ndash;25 kV anode) and mains-rectified bulk capacitors. Treat as lethal until measured otherwise &mdash; see [[Amstrad CPC 464 Maintenance Guide]] for the CRT discharge procedure.

== Identifying Your Unit ==

Most CPC 664 main PCBs are silkscreened with one of the following part-number ranges. The PCB rev is essentially identical across production:

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Amstrad CPC 664 main PCB revisions'''
! Silkscreen marking !! Gate Array !! CRTC type !! Notes
|-
| Z70200 / MC0030 (most common UK / EU 1985) || 40010 (CMOS) or 40007 (Ferranti, heatsinked) || HD6845SP (Type 0) || Original 1985 production
|-
| Z70200 / MC0030 later runs || 40010 || HD6845SP (Type 0) or UM6845R (Type 1) || Late 1985 production after 6128 launch
|-
| Schneider CPC 664 boards || same chip set as Amstrad, Schneider Computer Division part-number stamp || Type 0 or Type 1 || DACH region
|}

The 664 cabinet (parts 170301 family for the Amstrad UK version) is a flat all-in-one design with the keyboard at the front and the floppy drive bay at the rear-right. There is no cassette deck (vs the CPC 464) and no separate disc interface box (vs the CPC 464 + DDI-1).

== Opening the System Unit ==

Tools: Philips #1 and #2 screwdriver, anti-static strap.

# Power off the system and unplug the DC power from the monitor.
# Disconnect joystick, printer and expansion-port peripherals.
# Place the keyboard face-down on a soft cloth.
# Remove all screws on the underside of the case (typically 6&ndash;8).
# Lift the lower case carefully. The floppy drive and the keyboard membrane are both clipped to the upper case; the main PCB is on the lower case.
# Disconnect the floppy drive ribbon from the main PCB at the disc-controller area (typically a 26-pin or 34-pin header). Note pin 1 orientation &mdash; the red-striped wire goes to the pin marked '1' on both ends.
# Disconnect the keyboard ribbon at CP002.
# Optionally remove the floppy drive: 4 screws hold it to the upper case.

The floppy drive uses Hitachi part-number HD3.5R or HD3.5-1 (the Hitachi 3-inch single-sided mechanism, the same one used in the Amstrad CPC 6128 and the Sinclair ZX Spectrum +3). Replacement units can be sourced from another non-working 664 / 6128 / Spectrum +3, or modern hardware substitutes (Gotek + FlashFloppy firmware, Hxc emulator) can be fitted in the same bay using a 3-inch-to-Hxc adapter cable.

== Regular Cleaning ==

* Soft brush + low-pressure compressed air for the main PCB, the disc-controller area, the keyboard mat and the floppy drive head area.
* Clean the floppy R/W head with isopropyl alcohol on a foam swab. Do not use cotton-tipped swabs &mdash; cotton fibres in the head gap are a known cause of CRC errors and intermittent read failures.
* Clean the audio jack (J103), the 6-pin DIN video output (J101), the printer edge connector, the expansion edge connector and the joystick port (J102) with deoxidising contact cleaner sparingly on a foam swab.
* Clean the keyboard rubber-contact mats and the keyboard contact PCB as per [[Amstrad CPC 464 Maintenance Guide]] &mdash; the parts are identical.

== Floppy Drive Maintenance ==

The Hitachi 3-inch drive in the CPC 664 has three known wear items:

=== Drive belt ===

The drive belt is a thin (0.5 mm) flat rubber band that drives the disc spindle from a small pulley on the spindle motor. After 30+ years, the original belt is almost universally either liquefied (a sticky black residue on both pulleys) or stretched past usable tension. This is by far the most common 664 fault.

Symptom: '''disc not detected'''. The drive motor runs but the disc does not spin, or spins for a fraction of a second and stops. The system reports "Read fail" or hangs at CAT.

Procedure:
# Remove the floppy drive from the case.
# Remove the drive's metal top cover (2&ndash;4 screws).
# Locate the rubber belt running between the spindle motor pulley (at the front-left of the drive) and the disc spindle pulley (at the centre).
# If the original belt has liquefied, clean both pulleys thoroughly with IPA on a swab. The liquefied residue is a sticky black gum that can stop the new belt from gripping.
# Slip the new belt onto both pulleys. Modern replacement belts for the CPC 664 / 6128 / +3 are available from dedicated Amstrad shops &mdash; '''54 mm &times; 1 mm flat rubber drive belt''' is the most common spec, but verify by direct measurement of the pulleys.
# Verify the belt sits centred on both pulleys, and rotate by hand to confirm there is no slip.

=== Pinch roller and head pressure ===

Less common than the belt but eventually relevant. The pinch roller is the small rubber wheel that presses the disc against the spindle when a disc is inserted. After many disc insertions, the rubber hardens and develops flat spots, causing the disc to slip at high speed.

* Replacement pinch rollers for the Hitachi mechanism are available as modern silicone-rubber parts.
* Head load pressure: the head is sprung-loaded; do not adjust the spring tension by bending the bracket &mdash; the alignment is set at the factory and is not field-adjustable.

=== Worm drive / stepper lubrication ===

The stepper motor moves the head radially across the disc via a fine-pitch worm-drive lead screw. The worm drive needs '''light machine oil''' (e.g. clock oil or sewing-machine oil) every 5&ndash;10 years. Symptom of dried lubrication: stepper makes a chattering sound and the head fails to seek properly, often reporting "Track 0 error" or "Disk error" when accessing a known-good disc.

Procedure:
# Remove the drive's top cover.
# Locate the worm drive (a 2&ndash;3 mm-diameter threaded brass rod connecting the stepper motor to the head carriage).
# Apply a single drop of clock oil to the lead screw at the head carriage end and the stepper end.
# Move the head fully in and out by hand a few times to distribute the oil.
# Avoid getting oil on the head itself or on any belt or pulley.

== Head Alignment ==

The Hitachi 3-inch drive has factory-set head alignment that does not normally drift. Alignment is checked with a calibrated alignment disc (commercially '''Dysan 224/2A''' was the contemporary standard; modern equivalents are rare). For most field service:

* If the drive reads commercial diskettes reliably but fails to read user-formatted diskettes, the user-format diskettes were probably written by a misaligned drive. Reformat fresh diskettes from the suspect drive and test those.
* If the drive cannot read any commercial diskettes, suspect: drive belt (most common), head dirt, stepper lubrication, or in rare cases the head itself failed. Alignment is the last suspect.

If alignment is genuinely off, the procedure requires a service-grade alignment disc, a service-grade oscilloscope and the Hitachi alignment procedure from the drive service manual. This is normally beyond field service and the drive is typically retired in favour of a replacement.

== AMSDOS ROM Care ==

The CPC 664 fits a separate '''16 KB AMSDOS ROM''' (Amstrad part number 40015) at a dedicated socket on the main PCB, in addition to the main 32 KB OS+BASIC ROM at IC103 (40012). AMSDOS is the firmware that implements disc I/O and the |&nbsp;(bar) commands.

Common issues:
* '''AMSDOS ROM socket loose''': remove the ROM, clean the socket pins with IPA, refit firmly. Symptom: system boots to BASIC but CAT, LOAD"!", etc. report "ROM not present" or hang.
* '''AMSDOS ROM corrupted''': mask ROMs do not fail with age; if AMSDOS reports unexpected behaviour, suspect a bad disc, a bad drive cable, or a CRT/screen-corruption issue presenting as fake error messages. Verify by booting with a known-good test disc.
* '''Bypass / replacement''': community-developed ROM-based replacements for AMSDOS (e.g. ROMDOS, PARADOS) can be loaded into the AMSDOS socket. These add features such as 80-track double-sided support, larger directory entries, and faster sector access.

== Power Supply ==

The CPC 664 takes '''5 V DC at 2 A''' and '''+12 V DC at &asymp;0.6 A''' through the DC cord from the matching monitor. The CTM-644 colour monitor and the GT-65 green monitor both supply both rails on a multi-pin DC plug.

Unlike the 464 (which uses a single-pin 2.1 mm DC plug), the 664 / 6128 use a '''DIN-5 power cable''' or a stereo-3.5 mm-style multi-conductor cable, depending on the monitor.

If using a third-party display, a stand-alone '''5 V/2 A + 12 V/1 A''' dual-output PSU is required. The 12 V rail powers the floppy drive motor and stepper; the system unit and the floppy drive logic both run on 5 V.

== Connector Care ==

* '''Floppy drive ribbon''': the connector at the drive end is a 26-pin or 34-pin BERG header. Pin 1 is marked with a red stripe on the ribbon. Always align stripe-to-stripe; reversing the cable does not normally damage the drive but the drive will not respond.
* '''AMSDOS ROM socket''': inspect the IC socket for bent pins or oxidation. Reseat the ROM if disc commands are unreliable.
* '''Drive power tap''': on most 664s the drive power comes from the same connector as the main PCB power. If the drive motor fails to spin, verify +12 V at the drive power connector with a multimeter.
* '''Expansion port''' (50-pin PCB edge): same as CPC 464 with the exception that internal FDC means /EXP-FDC handshake is now slightly different.

== Capacitor Health ==

The 664 main PCB inherits all the [[Amstrad CPC 464 Capacitor Replacement Guide|CPC 464 capacitors]] in the non-cassette area, with the following changes:

* '''Cassette sub-PCB caps (C301, C303, C304, C306, C322, C315) are absent''' on the 664 because there is no cassette deck.
* The disc-controller area adds bypass capacitors near the NEC uPD765A FDC, near the AMSDOS ROM socket, and on the drive power input. Specific designators vary by board run; the most-failing positions in field service are the '''470 µF/16 V''' on the drive +12 V input and the '''10 µF / 22 µF''' caps near the FDC chip.

Full list with values and recap procedure: [[Amstrad CPC 664 Capacitor Replacement Guide]].

== Recommended Tools ==

* Philips #1 and #2 screwdrivers.
* Anti-static strap.
* Digital multimeter.
* IPA + foam swabs for head and connector cleaning.
* '''54 mm &times; 1 mm flat rubber drive belt''' (or measured equivalent).
* Modern silicone replacement pinch roller for the Hitachi 3-inch mechanism.
* Clock oil for the stepper worm drive.
* Soldering iron with fine tip + solder wick for capacitor work.
* 3-inch test diskette known to be good (an "Amsoft Demo" disc or a community-archived disc image).
* Optional: Gotek + FlashFloppy or Hxc emulator if the original Hitachi mechanism is beyond repair.

== Related Pages ==

* [[Amstrad CPC 664]]
* [[Amstrad CPC 664 Troubleshooting Guide]]
* [[Amstrad CPC 664 Capacitor Replacement Guide]]
* [[Amstrad CPC 464 Maintenance Guide]] &mdash; the keyboard and audio sections apply identically to the 664
* [[Recommended Tools]]

== References ==

* [https://archive.org/details/Amstrad_CPC664_Service_Manual_1985_Amstrad_Consumer_Electronics Amstrad CPC664 Service Manual] (1985, Amstrad Consumer Electronics). Authoritative source for the disc drive parts list, the disc-area schematic and the electrical parts list.
* [https://www.amstrad-noob.com/2020/02/08/replacing-the-fdd-drive-belt-on-the-new-cpc-664/ Replacing the FDD drive belt on the new CPC 664], Amstrad noob. Field-experience source for the drive belt replacement procedure.
* [https://www.cpcwiki.eu/index.php/Service_Manuals Service Manuals], CPCWiki. Index of CPC service-manual PDFs including the 664-specific volumes.

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