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Amstrad CPC 664 Maintenance Guide

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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 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 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

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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 (15–25 kV anode) and mains-rectified bulk capacitors. Treat as lethal until measured otherwise — see Amstrad CPC 464 Maintenance Guide for the CRT discharge procedure.

Identifying Your Unit

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

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

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

  1. Power off the system and unplug the DC power from the monitor.
  2. Disconnect joystick, printer and expansion-port peripherals.
  3. Place the keyboard face-down on a soft cloth.
  4. Remove all screws on the underside of the case (typically 6–8).
  5. 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.
  6. 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 — the red-striped wire goes to the pin marked '1' on both ends.
  7. Disconnect the keyboard ribbon at CP002.
  8. 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

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  • 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 — 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 — the parts are identical.

Floppy Drive Maintenance

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

Drive belt

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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:

  1. Remove the floppy drive from the case.
  2. Remove the drive's metal top cover (2–4 screws).
  3. 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).
  4. 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.
  5. Slip the new belt onto both pulleys. Modern replacement belts for the CPC 664 / 6128 / +3 are available from dedicated Amstrad shops — 54 mm × 1 mm flat rubber drive belt is the most common spec, but verify by direct measurement of the pulleys.
  6. Verify the belt sits centred on both pulleys, and rotate by hand to confirm there is no slip.

Pinch roller and head pressure

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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 — the alignment is set at the factory and is not field-adjustable.

Worm drive / stepper lubrication

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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 5–10 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:

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

Head Alignment

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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

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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 | (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

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The CPC 664 takes 5 V DC at 2 A and +12 V DC at ≈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

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  • 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

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The 664 main PCB inherits all the 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.

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  • Philips #1 and #2 screwdrivers.
  • Anti-static strap.
  • Digital multimeter.
  • IPA + foam swabs for head and connector cleaning.
  • 54 mm × 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.
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References

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