Amstrad 6128
The Amstrad CPC 6128 is the 128 KB, disc-based model of the Amstrad CPC range. It has the architecture of the Amstrad CPC 464 and 664 with 128 KB of RAM in two banks, a built-in 3-inch disc drive and CP/M Plus. Amstrad released it in the United States on 13 June 1985 and in Europe on 15 August 1985, where it replaced the 664; the UK prices were £299 with a green monitor and £399 with a colour monitor. The 6128 Plus replaced it in 1990.[1] It was sold with either the GT65 green monitor or the CTM644 colour monitor.[2]
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| CPC 6128 with its colour monitor | |
| Specifications | |
|---|---|
| Developer | Amstrad |
| Manufacturer | Amstrad Consumer Electronics plc |
| Type | Home computer |
| Released | 13 June 1985 (US), 15 August 1985 (Europe) |
| Discontinued | 1990 |
| Intro price | £299 with green monitor, £399 with colour monitor |
| CPU | Zilog Z80A at 4 MHz |
| Memory | 128 KB RAM in two 64 KB banks |
| Storage | Built-in 3-inch disc drive |
| Display | 160 × 200 (16 colours), 320 × 200 (4) or 640 × 200 (2) from 27 |
| Sound | General Instrument AY-3-8912, three voices |
| Graphics | 6845 CRT controller with gate array |
| ROM | 48 KB (operating system, Locomotive BASIC 1.1 and disc extensions) |
| Input | 74-key keyboard |
| Power | 5 V and 12 V DC from the monitor |
| OS / Firmware | Amstrad firmware, Locomotive BASIC 1.1, AMSDOS, CP/M 2.2 and CP/M Plus |
| Predecessor | Amstrad CPC 664 |
| Successor | Amstrad 6128 Plus |
| Model no. | CPC 6128 |
Power
The CPC 6128 has no mains connection and no power supply of its own. Amstrad's specification gives the supply as "Screen System: 240V AC 50Hz (keyboard and disc drive power supplied by screen system)", with a 5 mm socket for the 5 V supply, "supplied exclusively from monitor", and a 5 mm plug and lead to the 12 V disc power socket on the monitor.[2] The computer needs both. A 6128 that starts but cannot read a disc may simply have its 12 V lead unplugged. The monitors contain the mains supply and a CRT; the service manual gives a parts list, alignment instructions and a voltage chart for each, and CRT Discharge Procedure covers the hazard.[3]
Hardware
Amstrad's specification lists a Z80A at 4 MHz; 128 KB of RAM in two 64 KB banks, with over 41 KB available in BASIC and 61 KB of TPA under CP/M Plus; 48 KB of ROM containing BASIC, the operating system and the disc extensions; a 6845 CRT controller; an AY-3-8912 (three voices, eight octaves); an 8255 parallel interface; and a 74-key keyboard.[2] The external sockets are edge connectors for expansion and the Centronics printer, a second-drive socket (DI-2 lead), a 9-pin joystick socket, a 6-pin DIN for RGB or luminance video, a 5-pin DIN for an external cassette recorder (CL1 lead) and a 3.5 mm stereo output. Up to 252 additional 16 KB ROMs can be added. The keyboard unit measures 510 × 48 × 170 mm and weighs 2.0 kg.[2]
The parts list for the original board names the Z8400APS CPU (IC111), the TMM-23256P-1953 system ROM (IC103), the TMM-23128P-1851 AMSDOS ROM (IC204), the HSG3130/3170 gate array (IC116), a PAL16L8AC (IC118), sixteen MSM3764-20RS DRAMs (IC119–134), the µPD765AC-2 disc controller (IC201), the FDC9216BT data separator (IC202) and a 16 MHz crystal (X101).[3] The specification page prints the disc controller as "7653"; the parts list shows it is a µPD765AC-2.
Main board versions
CPCWiki's catalogue of photographed boards records three 6128 board versions.[4]
| Version | Silkscreen | Size | Notes |
|---|---|---|---|
| 1 | Z70210 MC0009A–C, MC0012A/B; Z70270 MC0016A | 320 × 155 mm | 8-pin data separator; pads for both the old and new gate array |
| 2 (©1985) | Z70290 MC0020A–I, MC0023D–G, MC0026B, MC0057A | 320 × 155 mm | 24-pin data separator; pads for the new gate array only |
| 3, cost-down (1988) | Z80330 MC0100A | 310 × 145 mm | 100-pin surface-mount gate array combining the gate array, PAL, CRTC and some floppy, DRAM and reset logic; can take four 64K × 4 RAM chips |
Amstrad's amendment manual has two later CPC6128 sections with their own board drawings.[5]
Disc system
The drive is a 3-inch unit to the Hitachi/Panasonic standard; the software is set for a 12 ms step rate and 30 ms settling time, and the system controls at most two drives. The discs are single-sided in use, 40 tracks of 512-byte sectors; the user turns the disc over, and each side has its own write-protect clip.[2] The parts list gives the drive as a Compact Floppy Disc Drive EME-155 (FDD201).[3] CPCWiki records that early 6128s used the earlier EME-150A.[6]
AMSDOS and CP/M Plus on the 6128 use two formats: SYSTEM, with 9 sectors per track, two reserved tracks and 169K of file space, and DATA only, with no reserved tracks and 178K. Amstrad notes that CP/M applications generally assume an 80-column screen, which the 6128 provides.[2]
Amstrad's service policy was that the drive mechanism and its board, PCB30001, went back for exchange; the manual gives no part numbers for that board but includes its circuit diagram.[3] The usual fault is a perished drive belt; CPCWiki gives the replacement as 3 mm wide, 0.6 mm thick and 230 mm in outer circumference, and describes the removal procedure for the 6128.[7]
Capacitors
The parts list gives twelve electrolytic capacitors on the original board.[3]
| Value | Circuit reference | Amstrad part no. |
|---|---|---|
| 100 µF / 16 V | C315 | 20028 |
| 100 µF / 10 V | C301, C304 | 20028 |
| 47 µF / 10 V | C136, C303, C306 | 1400244 |
| 22 µF / 10 V | C308 | 20025 |
| 1 µF / 50 V | C309, C311, C314, C317, C318 | 20062 |
Documentation
- Amstrad CPC 6128 Service Manual – Amstrad's service manual for the CPC 6128, CTM644 and GT65
- Amstrad CPC 464 / CPC 6128 / GT65 / CTM644 / MP3 / CT1 Service Manual Amendment – later 6128 boards
- Amstrad 464 Plus / 6128 Plus / GX4000 Service Manual – the 6128 Plus
Related pages
- Amstrad CPC 464 · Amstrad CPC 664
- Amstrad CPC 664 Maintenance Guide and Amstrad CPC 664 Troubleshooting Guide – the 664 uses the same disc system design
- Floppy Drive Repair · Capacitor Failure Symptoms · CRT Discharge Procedure
References
- ↑ Wikipedia, "Amstrad CPC", sections "CPC 6128" and "CPC 664". Retrieved 2026-10-01. Gives the US and European release dates, the launch prices, the replacement of the 664 and the 1990 replacement by the 6128plus.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Amstrad Consumer Electronics plc, CPC6128 Micro Computer / CTM644 Colour Monitor / GT65 Green Monitor Service Manual, back page "Technical Specification". Described at Amstrad CPC 6128 Service Manual.
- ↑ 3.0 3.1 3.2 3.3 3.4 Amstrad Consumer Electronics plc, CPC6128 Micro Computer / CTM644 Colour Monitor / GT65 Green Monitor Service Manual, p. 2 "Contents" and p. 21 "Electrical Parts List". Described at Amstrad CPC 6128 Service Manual.
- ↑ CPCWiki, "Mainboard Versions". Retrieved 2026-10-01. Community catalogue of board markings, sizes and per-version changes.
- ↑ Amstrad plc, CPC464 / CPC6128 / GT65 / CTM644 / MP3 / CT1 Amendment Service Manual, contents and pp. 11–24. Described at Amstrad CPC 464 / CPC 6128 / GT65 / CTM644 / MP3 / CT1 Service Manual Amendment.
- ↑ CPCWiki, "Amstrad FDD part". Retrieved 2026-10-01. Lists the Matsushita mechanisms used in the CPC range and their differences.
- ↑ CPCWiki, "Changing the drive belt". Retrieved 2026-10-01.