Amstrad PC1640 Maintenance Guide
The Amstrad PC1640 shares its case, cell tray, floppy drives and supply-in-the-monitor layout with the Amstrad PC1512, and the Amstrad PC1512 Maintenance Guide covers those parts in detail. What differs on the PC1640 is set out below: the display switches, the three monitors and their supply settings, the hard disc models and the internal fourth slot. Amstrad's service manual is the source for the settings below.[1]
Safety
[edit | edit source]Warning: each monitor holds a mains switch-mode supply for the whole computer and a CRT.
- Discharge the tube before working inside a monitor; see CRT Discharge Procedure.
- Amstrad's PC1640 safety tests after servicing are a 1.5 kV RMS flash test for 3 seconds between the mains poles and exposed metal, an insulation test at the same voltage requiring more than 4 MΩ, and an earth continuity test requiring the mains lead to be under 0.5 Ω.[1] The PC1512 manual specifies 3 kV for its monitors.[2]
- All three monitors use a 3.15 A mains fuse, F501.[1]
Display switches
[edit | edit source]The ten DIP switches on the back of the system unit, marked "Display selector", configure the internal graphics adaptor and must match the monitor; a PC1640 that runs but shows nothing may simply have its switches set for another display. Amstrad's chart on page 19 of the service manual:[1]
| Monitor | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| PC-MD | Off | Off | On | Off | On | On | On | Off | Off | Off |
| PC-CD | Off | Off | Off | On | On | On | On | Off | Off | Off |
| PC-ECD | Off | On | On | Off | Off | On | On | On | Off | Off |
The same page names each start-up mode set by SW1–SW5. The DISPLAY command on the system discs accepts these names and can override the switches.[1]
| Mode | SW1 | SW2 | SW3 | SW4 | SW5 | Display | Description |
|---|---|---|---|---|---|---|---|
| MDTEXT | Off | Off | On | Off | On | PC-MD | MDA or Hercules; recommended for the PC-MD |
| MDMONO | Off | Off | On | Off | Off | PC-MD | EGA monochrome |
| CDMONO | Off | Off | Off | On | On | PC-CD | CGA-compatible 80 column; recommended for the PC-CD |
| CDCOLOR | Off | Off | Off | On | Off | PC-CD | EGA-compatible 80 column |
| ECD200 | On | On | On | Off | Off | PC-ECD | EGA, 200 lines |
| ECD350 | Off | On | On | Off | Off | PC-ECD | EGA, 350 lines; recommended for the PC-ECD |
For every mode SW8 is on for the PC-ECD and off for the PC-MD or PC-CD, and SW9 and SW10 are off.[1] On the 9-way video plug, SW8 decides whether pin 2 is grounded or carries the secondary red signal.[3] John Elliott's switch page prints CDCOLOR with SW5 on, the same as CDMONO; Amstrad's chart has SW5 off for CDCOLOR.[4] SW10 on disables the internal adaptor, and SW6 and SW7 then tell the BIOS which add-in card is fitted.[4] An owner who could not get a picture after a repair found the switches had been knocked; setting them back for the PC-MD restored the display.[5]
Backup cells and case
[edit | edit source]The clock and configuration memory run from four AA cells in a tray under the monitor, as on the PC1512.[3] On a Schneider PC 1640, cells left in the tray leaked down onto the main board around the CPU, corroding the CPU and 8087 sockets; the CPU had failed.[6] Remove old cells, clean the tray and check the board under it; see Battery Explosion, Capacitor or Corrosion Damage.
The case opens with seven screws: two under the stand-offs, two under the plate over the card slots and three holding the cards. One owner found the fan under the hard disc with its blades detached.[7] Check that fan on hard disc models. Besides the three slots under the rear cover there is a fourth slot inside the case, intended for a hard card.[8][9]
Floppy and hard discs
[edit | edit source]The FD-3 drive procedures are on pp. 3–14 of the PC1640 manual, with a Dysan 224/2A CE diskette listed for alignment; the checks are the same as in the PC1512 guide.[1] The floppy cable is soldered to the main board. Drive A: is jumpered DS0 and drive B: DS1, and the motor-on line is shared, so drive A:'s motor turns when B: is used. The built-in controller does not support high-density discs; a Gotek emulator works as drive B: with 720K or 360K images.[10][11]
Hard disc models used a 20 MB drive from Alps (175037) or Tandon (60001); Amstrad says hard disc units must not be opened.[1] To reinstall the system software, page 18 gives HDFORMAT, FDISK, FORMAT C:/S and CONFIG, run from system discs 1 and 4. Amstrad allows one bad sector per megabyte, 200K on a 20 MB disc; CHKDSK reports them and HDFORMAT does not reduce them.[1] DOS Days records the hard disc models as fitted with a hard card, a MiniScribe RLL drive and controller on one card.[11] For a replacement, DOS Days got an XT-CF-Lite working at base address 300h, control block 328h, "2x8-bit" bus type and interrupts disabled, with its ROM at DE00h; see Hard Drive Maintenance and Repair.[10]
Power supply checks
[edit | edit source]Each monitor sets the computer's rails to the same targets, with its own presets.[1]
| Rail | Target | PC-MD preset | PC-CD and PC-ECD preset |
|---|---|---|---|
| +5 V | 5.10 V ±0.02 V | VR505 | VR604 |
| +12 V | 12.15 V ±0.02 V | VR504 | VR603 |
| −5 V | 5 V ±0.05 V (magnitude) | VR501 | VR601 |
| −12 V | 12.0 V ±0.05 V (magnitude) | VR502 | VR602 |
| +12 V protection | Trips at 4.5 A through a dummy load | VR507 | VR606 |
| Monitor +12 V | 12.0 V at test point E | VR503 | – |
The rails can be measured at the 14-way DIN plug: +5 V on pins 3 and 5, +12 V on pin 11, −12 V on pin 9, −5 V on pin 13, 0 V on pins 2, 4, 8, 10 and 12.[3] The rest of each alignment table covers that monitor's picture. The PC-ECD has a cooling fan; check that it turns.[8]
Processor upgrade
[edit | edit source]The 8086 can be replaced with an NEC V30 in the same socket. DOS Days measured an average gain of about 22% across a set of benchmarks at the same 8 MHz clock.[12] John Elliott notes that Windows 3.0's colour drivers need a V30 on the PC1640.[13]
Checklist for a newly acquired PC1640
[edit | edit source]- Remove the AA cells and inspect the tray and the board beneath it.
- Note the DIP switch settings before touching anything, and check them against the monitor fitted.
- Open the monitor, discharge the tube and inspect the supply area; see the Amstrad PC1640 Capacitor Replacement Guide.
- Measure the rails at the DIN plug.
- On hard disc models, check the fan under the hard disc.
- Clean the floppy heads and check the drive select jumpers.
Related pages
[edit | edit source]- Amstrad PC1640 · Amstrad PC1640 Troubleshooting Guide · Amstrad PC1640 Capacitor Replacement Guide
- Amstrad PC1512 Maintenance Guide
- Amstrad PC1640 Service Manual · Amstrad PC1640 VDU Tests Manual
- Floppy Drive Repair · Hard Drive Maintenance and Repair · 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 Amstrad plc, PC1640 Personal Computer, PC-MD Monochrome Display, PC-CD Colour Display, PC-ECD Enhanced Colour Display Service Manual. Hosted as File:Amstrad PC1640 Service Manual.pdf, described at Amstrad PC1640 Service Manual. Safety tests p. 2; servicing note p. 3; FD-3 maintenance pp. 3–14; hard disc installation p. 18; switch settings p. 19; bad sectors and RP5-2 p. 20; monitor alignment instructions pp. 40, 41 and 47.
- ↑ Amstrad plc, PC1512 Personal Computer, PC-MM Monochrome Monitor, PC-CM Colour Monitor Service Manual. Hosted as File:Amstrad PC1512 Service Manual.pdf, described at Amstrad PC1512 Service Manual. Safety test p. 2.
- ↑ 3.0 3.1 3.2 Amstrad, PC1640 Technical Reference Manual, section 1, transcribed by John Elliott: seasip.info. Retrieved 2026-10-02. Section 1.9 (clock and four AA cells), 1.20 (9-way video connector and switch 8), 1.21 (power connector).
- ↑ 4.0 4.1 John Elliott, "PC1640 DIP switches", seasip.info, 12 April 2003. Retrieved 2026-10-02. SW1–SW5 combinations including secondary-adapter modes, SW6–SW7 fonts, SW8 monitor type, SW9 32K EGA ROM, SW10 disabling the internal adaptor.
- ↑ jarcher1701, austfox, modem7 and others, "Amstrad PC1640 – Faulty Floppy Disk Controller or Disk Drive", Vintage Computer Federation Forums, October–December 2023. Retrieved 2026-10-02. Community repair thread: the floppy controller error traced to C124 and R181, the LK1–LK3 bypass, a blank screen after the repair cured by resetting the DIP switches for the PC-MD.
- ↑ Wobblestone, "Amstrad 1640 (germany: Schneider PC 1640) with battery damage, works 'a little', has address problems", Vintage Computer Federation Forums, November–December 2024. Retrieved 2026-10-02. Community repair report: AA cell leakage onto the CPU area, corroded sockets, a dead CPU, and a later address-line fault after the socket was replaced.
- ↑ weedeewee, reply in "How to withdraw hard disk from amstrad pc1640", VOGONS, 25 November 2021. Retrieved 2026-10-02. Community instructions: seven case screws and lifting the top half; the fan under the hard disc with its blades fallen off.
- ↑ 8.0 8.1 DOS Days, "Amstrad PC1512 and PC1640". Retrieved 2026-10-02. The fourth internal ISA slot for a hard card, the AA cell tray, the drive select jumpers, the 14-pin DIN pinout.
- ↑ John Elliott, "Amstrad XTs: Models", seasip.info, 19 April 2013. Retrieved 2026-10-02. Four full-sized ISA slots on the PC1640, one hidden inside the case.
- ↑ 10.0 10.1 DOS Days, "The Amstrad PC1640 Project – Part 2", 18 August 2026. Retrieved 2026-10-02. The soldered floppy cable, the Gotek as drive B:, the shared motor line, no high-density support, the XT-CF-Lite configuration that worked, memory parity errors.
- ↑ 11.0 11.1 DOS Days, "The Amstrad PC1640 Project – Part 1", 17 August 2026. Retrieved 2026-10-02. Drive A: jumpered DS0 and drive B: DS1, the Amstrad-branded drive boards, the main board revisions.
- ↑ DOS Days, "The Amstrad PC1640 Project – Part 3", 20 August 2026. Retrieved 2026-10-02. The V30 fitted in place of the 8086 and the benchmark comparison, the clock arrangement with the 24 MHz crystal, the 16.25 MHz dot clock.
- ↑ John Elliott, "Amstrad XTs: Questions and answers", seasip.info, 26 June 2019. Retrieved 2026-10-02. Windows versions on Amstrad XTs and the V30 requirement for colour drivers, NVR, system discs.