Amstrad CPC 664 Troubleshooting Guide
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The Amstrad CPC 664 has no numbered self-test codes. Amstrad's service manual gives two charts for diagnosis: a basic hardware analysis for the computer and a four-page diagnostic flow chart for the disc drive, with measured thresholds.[1] The disc mechanism procedures are in the Amstrad CPC 664 Maintenance Guide. The keyboard, sound and ports follow the 464 design; see also the Amstrad CPC 464 Troubleshooting Guide.
Power first
[edit | edit source]The CPC 664 has no mains supply of its own. Its 5 V and the disc drive's 12 V both come from the CTM644 or GT65 monitor, on separate leads.[1] A computer that starts normally with a completely dead drive may simply have no 12 V. The monitors contain the mains supply and a CRT; see CRT Discharge Procedure.
A working 664 starts with "Amstrad 64K Microcomputer (v2)", the Amstrad and Locomotive Software copyright line, "BASIC 1.1" and "Ready".[2] A German Schneider machine shows "Schneider" in place of "Amstrad". The name is chosen by links LK1–LK3 on the main board, read through the 8255's port B: no links gives Amstrad, LK2 alone gives Schneider and LK1 with LK2 gives Awa, used on Australian machines. An unexpected name at start-up is a link setting, not a ROM fault.[3]
Amstrad's basic hardware analysis
[edit | edit source]| Symptom | Check | Amstrad's suspects |
|---|---|---|
| Red LED does not light | Monitor mains fuse; 5 V DC present on the cable from the monitor | Mains fuse; cable or plug assembly from the monitor. With 5 V present: internal connectors and soldered joints (faulty LED, broken PCB track, faulty connector), then the switch on the keyboard unit |
| LED lights, no start-up message | RGB video connector inserted; brightness turned up; any picture at all? | With a picture: video connector, cable assembly, ULA or PCB. No picture: try another monitor. Works on another monitor: the monitor's cable termination, internal connectors or brightness control. Still nothing: ULA, Z80A, 6845, crystal or RAM |
| No reaction to the keyboard | Keyboard connector | Keyboard connector |
| Some keys do not work | Keyboard PCB | Cracks, liquid spillage or distorted mounting; connector lead and termination |
| Program disc does not load | Try another disc | If another disc loads, replace the disc; if not, go to the disc flow chart |
| No sound | – | Audio amplifier or speaker, volume control, audio connector plug or socket, AY-3-8912 sound IC |
The ULA is the gate array, IC116 (HSG3130/3170, part 40010). The other suspects are the Z80A (IC111), the 6845 (IC108), the crystal (X101) and the eight HM4864U-2 DRAMs (IC117–124).[1] Amstrad's manual refers full CPU diagnostics to its RP1 Test Pack.[1]
Disc faults: Amstrad's diagnostic flow chart
[edit | edit source]The flow chart is marked for information only and was meant to be used with the alignment procedures; Amstrad's service agents returned faulty mechanisms rather than repairing them.[1] It needs a double-beam oscilloscope and the EME-CF2 test disc. The drive's test points are TP1 and TP2 (read signal at the filter outlet), TP3 and TP11 (signal ground), TP5 (track 00 sensor output) and TP9 (index).[1]
Top level (chart 3-A)
[edit | edit source]- Index period 200 ±5 ms? If not, go to the motor rotation chart.
- Self-read error? Go to the read error chart.
- Write error? Go to the write error chart.
- Interchangeable with other drives? If not, go to the interchangeability chart.
200 ms is one revolution at 300 rpm.[4]
Motor rotation (chart 3-B)
[edit | edit source]| Question | Action |
|---|---|
| Does the motor rotate? | If not: is power supplied? If not, check the wiring, including the 12 V lead from the monitor |
| Can it be adjusted with VR201? | If so, adjust to 200 ±1 ms |
| Does it rotate normally with a known-good motor? | If so, replace the motor; if not, replace the drive |
A motor that runs while the disc does not turn usually has a perished belt; see the Amstrad CPC 664 Maintenance Guide.
Read errors (chart 3-C)
[edit | edit source]Tested with the EME-CF2 disc:[1]
| Check | If it fails |
|---|---|
| Track 39 "2F" output 140 mV or more? | Is head touch OK? If not, replace the drive. If so, is head output 1 mV or more? If not, replace the head assembly; if so, replace the drive |
| Track 00 output 220 mV or less? | Follow the head checks above |
| Read/write errors on all tracks? | Follow the head checks above |
| Read error on one specific track only? | Replace the disc |
| Seek error? | Is the track 00 sensor output normal? If so, replace the drive; if not, replace the track 00 sensor |
A read error on a single track points to the disc, not the drive.
Write errors (chart 3-D)
[edit | edit source]| Check | Action |
|---|---|
| Is the error continuous? | If not, work through the seek and read failure checks |
| Write waveform present at TP1, TP2? | If not, is the head connector open or short? Open: repair the head connector. Short: replace the control PCB |
| Waveform OK, error persists | Amplifier system: replace the control PCB. Head system: replace the drive |
Interchangeability
[edit | edit source]If a drive works with its own discs but not with discs from other machines, Amstrad's chart runs an off-track media test in each direction (fail: adjust positioning), then checks index timing against a 0–1000 µs window (fail: adjust index timing; pass: the media has failed).[1]
Soft, write and seek errors
[edit | edit source]The software-errors page sets out what to try before blaming the drive:[1]
- Soft errors come from short bursts of external noise or from small off-tracking and write-timing shifts. Re-read the track ten times or more; if that fails, step the head to the adjacent track in the same direction as the last move, return, and re-read. If that fails too, the error cannot be recovered.
- A write error is normally caught by the write-check read on the next rotation. Repeat the write; if it still fails after more than ten attempts, try another track and then another disc. If the error moves with the disc, discard the disc; if it stays, the drive is defective.
- Seek errors come from the stepper motor or its drive circuit, or from incorrect carriage torque. Recalibrate to track 00 and seek again.
The same page notes that the drive is not ready until two revolutions after a disc is inserted, and to keep the head clean.[1]
AMSDOS error messages
[edit | edit source]When AMSDOS meets a hardware problem it follows the message with "Retry, Ignore or Cancel?".[2]
| Message | Amstrad's explanation |
|---|---|
| Unknown command | The command is not spelt correctly |
| Bad command | The command cannot be carried out: syntax error or unsuitable hardware configuration |
| filename already exists | Renaming to a name already in use |
| filename not found | The file does not exist |
| Drive x: directory full | No more room in the disc directory |
| Drive x: disc full | No more room on the disc |
| Drive x: disc changed, closing filename | The disc was changed with files still open |
| filename is read only | The file is set read-only (set and cleared under CP/M) |
| Drive x: disc missing | No disc, or the disc is not seated and spinning; eject, re-insert and press R |
| Drive x: disc is write protected | The disc's write-protect hole is open |
| Drive x: read fail | Hardware error reading the disc; eject, re-insert and press R |
| Drive x: write fail | Hardware error writing the disc |
| Failed to load CP/M | Read error loading CP/M, or the disc is not a valid system disc |
CP/M loads only from a SYSTEM-format disc, the format that reserves two tracks for it; DATA-format discs have no reserved tracks.[1]
Other faults
[edit | edit source]- Sound: Amstrad's suspects are the audio amplifier (IC301, LA4140) or speaker, the volume control, the audio connector and the AY-3-8912 (IC102).[1] The 300-series audio circuit holds most of the board's electrolytic capacitors; see the Amstrad CPC 664 Capacitor Replacement Guide.
- CRTC differences: Amstrad fitted 6845 CRTCs from several makers, which CPCWiki groups into types with small behavioural differences. The 664 parts list specifies the Hitachi HD6845SP (type 0).[1][5] Some demos that rely on undocumented CRTC behaviour run differently from one type to another; that is not a fault.
- Keyboard, printer and expansion port: as on the 464; see the Amstrad CPC 464 Troubleshooting Guide.
Related pages
[edit | edit source]- Amstrad CPC 664 · Amstrad CPC 664 Maintenance Guide · Amstrad CPC 664 Capacitor Replacement Guide
- Amstrad CPC 664 Service Manual
- Amstrad CPC 464 Troubleshooting Guide
- Floppy Drive Repair · Capacitor Failure Symptoms · Recommended Tools
References
[edit | edit source]- ↑ 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 Amstrad Consumer Electronics plc, CPC664 Micro Computer / CTM644 Colour Monitor / GT65 Green Monitor Service Manual. Described at Amstrad CPC 664 Service Manual. Basic hardware analysis p. 4; software errors p. 7; diagnostic flow chart pp. 8–11; alignment checks pp. 12–15; electrical parts list p. 21; technical specification on the back page.
- ↑ 2.0 2.1 Amstrad Consumer Electronics plc, CPC664 User Instructions, chapter 1 (start-up display) and chapter 5, pp. 13–15 "Reference guide to AMSDOS Error Messages". Scan at archive.org.
- ↑ CPCWiki, "LK-selectable Brand Names". Retrieved 2026-10-01.
- ↑ CPCWiki, "Amstrad FDD part". Retrieved 2026-10-01. Drive speed (300 rpm, 200 ms index period) and the VR201 adjustment on the EME-150A.
- ↑ CPCWiki, "CRTC". Retrieved 2026-10-01. Lists the CRTC parts Amstrad used and their type numbers.