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Amstrad ALT-386SX Maintenance Guide

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ALT386SX main PCB, top view (Amstrad service manual p. 16)

The Amstrad ALT-386SX is a 7 kg mains and battery portable with an internal mains power supply, a 12 V NiCd battery pack, a rechargeable backup battery on the main board, a hard disk, a floppy drive and a backlit LCD. Most of its parts, including the supply, the display, the VGA board, the keyboard and the battery pack, are shared with the Amstrad ALT-286, and the procedures below apply to both apart from the main and memory boards. Amstrad's service manual gives parts lists and schematics but no procedures; the procedures below come from owners' restoration reports, cited as community experience.[1][2] Faults are in the Amstrad ALT-386SX Troubleshooting Guide and capacitors in the Amstrad ALT-386SX Capacitor Replacement Guide.

Safety

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Warning: the power supply inside the case runs from the mains, and its heatsinks are live.

  • Unplug the mains lead and remove the battery pack before opening the case.
  • The power supply board in oldcrap.org's photographs is marked RPS-07M-1 and carries two fuses, F1 "250V T2A" and F2 "250V 2A", and a printed warning that the heatsink presents a risk of electric shock and should be tested before touching.[2] Treat the supply's reservoir capacitor as charged until you have measured it.
  • The rating label of an ALT-286, which uses the same supply, gives the mains input as 120–240 V, 50/60 Hz, 60 W, rated current 730–440 mA.[3]
  • After any repair, Amstrad's safety tests are a 1.5 kV RMS flash test for 3 seconds between the mains poles and all accessible metal, an insulation test at the same voltage requiring more than 4 MΩ, and a mains-lead earth resistance of no more than 0.5 Ω.[1]

Battery pack

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The BAT-1 pack, rated 12 V 2400 mAh NiCd, shared by both models

The removable pack is type BAT-1, rated 12 V 2400 mAh NiCd, and is the same part (270450) for both models.[3][1] Amstrad's specification gives two hours' use and a two-hour "Quick Charge"; New Computer Express found that the pack charges slowly while the machine runs from the mains and quickly with it switched off.[1][4]

Backup battery on the board

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Owners describe the backup battery on the main board leaking and corroding the tracks and vias around it; one owner traced further damage under U144 to the surface-mount capacitor C121 beside the memory connector, which had also leaked.[2] oldcrap.org's repair cleaned the board with vinegar, rinsed it with water, removed the worst-affected chips, scraped back the solder resist to expose the tracks, mapped the damage from photographs and rebuilt the broken tracks with fine wire, then sealed them with PCB lacquer.[2]

The original cell is rechargeable and the board charges it. In the comments, the author agreed that the non-rechargeable button cell he had fitted should come out because the board would try to charge it; another reader suggested a series diode to block the charge current, and another owner fitted a 300 mAh NiMH pack.[2] Replace the cell with a rechargeable one, or block the charging path before fitting a primary cell. Relocating the new cell away from the board, as one owner did, keeps any future leak off the tracks.[2]

One owner who had replaced the backup battery and the hard disk saw "Invalid configuration information – please run setup program" at start-up; pressing F1 let the machine boot.[2]

Configuration switches

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Two sets of switches on the back of the machine set the memory size, clock and display. On oldcrap.org's machine, OFF is switch up and ON is switch down:[2]

ALT-386SX memory size switches
SW1 SW2 SW3 Memory
OFF ON ON 512 KB
ON OFF ON 1 MB
OFF ON OFF 2 MB
ON OFF OFF 4 MB
Other switches
Switch Function ON OFF
SW4 Page mode Always ON –
SW5 Wait states – Always OFF
SW6 Clock 8 MHz 16 MHz
SW7 Display Colour Black and white
SW8 Serial Enabled Disabled
SW9 Pipeline Always ON –
SW10 Drive B type – Always OFF

For a first power-up after repair, the author recommends the smallest memory setting and the internal display. If the switches claim more memory than is fitted, the BIOS reports it with a beep code.[2] The parts list gives a 10-way DIP switch (SW101, KSP10) and a 2-way DIP switch (SW501, KSP02).[1]

Memory

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The memory bay under the base of an ALT-286, with four SIMMs, the BIOS EPROMs and an empty socket

The SIMMs sit in a bay under a cover in the base.[3] On the ALT-386SX they are on the ROM/RAM board, organised as two columns (0 and 1) of two rows: each column needs a pair of SIMMs, one in row 1 for data bits 0–7 and one in row 2 for bits 8–15, and column 0 must always be filled because the machine boots from it.[2] oldcrap.org gives a table of the SIMM signals to the VL82C202, VL82C203, VL82C204 and VL82C205 chips, some of them through resistors in the R321–R340 range on the underside of the board, for checking continuity after corrosion.[2]

Hard disk and floppy drive

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Amstrad fitted a 40 MB voice-coil disk with 25 ms access to the ALT386SX.[1] oldcrap.org's machine has a Sony SRD3080C-50 of 80 MB, set as BIOS drive type 24, and a TEAC FD-235HF floppy drive.[2] One owner whose Sony drive had failed (its activity light stayed on and FDISK reported read errors) fitted a 1 GB Quantum Fireball IDE drive that has the same small three-pin power connector, and set a user-defined geometry in the BIOS to get about 500 MB under MS-DOS 5.0.[2] See Hard Drive Maintenance and Repair and Floppy Drive Repair.

Display

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The LCD is a backlit 640 × 480 panel, 223 × 169 mm, with 32 grey scales.[1] oldcrap.org's machine has an Epson EG9005-F-LS-2 panel; New Computer Express also names Epson.[2][4] The backlight is driven from the LCD inverter board (PCB7, DC/AC, part 270356FTZ) with its transformer T701 (FN-1051).[1] The display has contrast and brightness knobs and an invert switch that reverses the grey scale.[4]

Fan and keyboard

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  • The cabinet parts list includes a fan motor, type 0410-12 (UN-7, part 270505). Clean its blades and the vents with a soft brush and low-pressure air.[1]
  • The 85-key keyboard is a single unit (UN-2, part 270465). Amstrad supplied a set of country keycaps with a key puller (part 270445).[1][4]

Tools

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  • Cross-head screwdrivers and an anti-static strap
  • Digital multimeter
  • Fine-tip soldering iron, desoldering braid and thin insulated wire for track repairs
  • Isopropyl alcohol, white vinegar and distilled water for leak damage
  • See Recommended Tools.
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References

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  1. ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 Amstrad plc, ALT286 / ALT386SX Laptop Computer V.FTZ Service Manual. Described at Amstrad ALT-286 / ALT-386SX Service Manual. Technical specification and safety tests p. 2; LCD inverter PCB p. 3; electrical parts lists pp. 10–11; cabinet parts list p. 12; exploded view p. 13.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 Pawel Pieczul, "Amstrad ALT-386SX", oldcrap.org, 24 August 2020, with readers' comments to 2024. Retrieved 2026-10-01. Parts fitted, configuration switches, PSU recap, SIMM wiring and battery-leak repair on one ALT-386SX; further repairs reported by owners in the comments.
  3. ↑ 3.0 3.1 3.2 Bibliothèque nationale de France, Collection Charles Cros no. 1008, ALT-286 photographs 15, 18 and 19 of 26, on Wikimedia Commons. Retrieved 2026-10-01. The rating label, the memory bay and the BAT-1 battery label.
  4. ↑ 4.0 4.1 4.2 4.3 Keith Pomfret, "Heavy weight lightweight", New Computer Express no. 92 (1990). Transcribed at CPCrulez. Retrieved 2026-10-01.


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