RetroTechCollection

Amstrad ALT-386SX Troubleshooting Guide

Amstrad's service manual for the Amstrad ALT-386SX has parts lists and schematics but no fault-finding charts, test points or voltage tables, and treats the power supply as a sealed unit.[1] The faults below are those owners have reported and fixed, cited as community experience, mostly from the oldcrap.org restoration of an ALT-386SX and the repairs described in its comments.[2] The Amstrad ALT-286 shares the supply, display, VGA board and keyboard, so most of this applies to it; see the Amstrad ALT-286 Troubleshooting Guide for its own reports. Procedures are in the Amstrad ALT-386SX Maintenance Guide.

Amstrad ALT-386SX (photo: MrCauldron, CC BY 3.0)

Power

edit
Power faults
Symptom Probable cause Action
Dead, or hard disk spins but no beep and no picture Power supply output low Recap the power supply; see the Amstrad ALT-386SX Capacitor Replacement Guide
12 V missing or intermittent Short cable from the supply to the main board Check the contacts in the 7-wire plug and socket
Runs on mains, not on battery Battery pack Check the pack and its terminals; see Battery Refurbishment

oldcrap.org found that every electrolytic capacitor in the machine's Rubycon RPS-07 supply had leaked, leaving the output voltages much lower than required; replacing them restored the correct levels.[2] Other owners report the same supply recapped with "some of the caps def bad", and a machine whose 12 V failed intermittently because contacts had failed in the 7-wire plug of the inch-long cable from the supply to the main board.[2]

Owners list the supply's outputs differently. One reader measured 5 V, 5 V, 12 V, −12 V and −19 V with two grounds on the main power connector; another, testing an ALT-286 supply on the bench, found +5 V, −12 V and −24 V but no +12 V after a recap.[2] Amstrad publishes no voltage table for the supply.

The rating label of the related ALT-286 gives the limits for an expansion card: +5 V at 0.6 A, +12 V at 0.1 A, −12 V at 0.02 A and −5 V at 0.02 A.[3]

Start-up and BIOS

edit

The BIOS is a Phoenix BIOS, entered with F2 during boot or Ctrl-Alt-S at the DOS prompt, and it reports power-on self-test failures as beep codes on the speaker.[2] The memory bay of an ALT-286 shows an EPROM carrying a Phoenix Technologies label.[4]

Start-up faults
Symptom Probable cause Action
Beep code for memory Memory switches set higher than the RAM fitted; SIMM missing; corroded tracks Set SW1–SW3 to the smallest size; check that column 0 has a pair of SIMMs; check the SIMM tracks for leak damage
"Invalid configuration information – please run setup program" Setup lost after the backup battery was disconnected or replaced Run setup with F2 and enter the drive type; F1 continues the boot
Setup screen appears with F2 but the machine hangs Unresolved in the reports Owners suggest checking every supply rail, recapping the supply and reseating the RAM and cables

The memory-size switches and the SIMM arrangement are tabled in the Amstrad ALT-386SX Maintenance Guide. oldcrap.org traced its memory errors to tracks dissolved by a leaking backup battery and rebuilt them with wire, checking each SIMM signal through to the VL82C202, VL82C203, VL82C204 and VL82C205 chips.[2]

Display

edit

If the machine boots (the disk and floppy can be heard) but the LCD is blank, check the display switches on the back (SW7 selects colour or black and white) and the connector of the VGA card before suspecting the panel. A reader whose screen flickered and went blank, with nothing on the external VGA port either, found no voltage on the VGA card's power connectors CN502–CN506; the author suggested the card's connector or the display switches.[2] The VGA board (PCB4, part 270563) is common to both models and uses Cirrus Logic CL-GD620 and CL-GD610 controllers.[1] The backlight is driven by the inverter board PCB7 (DC/AC).[1]

Disks

edit
  • Hard disk activity light on all the time, "Hard disk controller failure", long delays at boot and FDISK reporting read errors: one owner's original Sony SRD3080C-50 had failed, and a replacement IDE drive cured it.[2]
  • Hard disk not recognised after the backup battery was replaced: re-enter the drive type in setup. oldcrap.org's 80 MB Sony is type 24.[2]
  • See Hard Drive Maintenance and Repair and Floppy Drive Repair.

Sound

edit

A speaker that has become quiet points to a leaking surface-mount electrolytic. One owner, who had found the 33 µF capacitor C121 beside the memory connector leaking and the tracks under U144 corroded, replaced the capacitor that had damaged his board with a tantalum part and noted that it is in the speaker circuit, so low speaker volume is the warning sign. Another owner, whose speaker was barely audible, found a leaking surface-mount capacitor and replaced it with a standard electrolytic, and the sound returned.[2] The speaker circuit is on the peripheral schematic (p. 23), which serves both models.[1] Remove a leaking part promptly.

edit

References

edit
  1. ↑ 1.0 1.1 1.2 1.3 Amstrad plc, ALT286 / ALT386SX Laptop Computer V.FTZ Service Manual. Described at Amstrad ALT-286 / ALT-386SX Service Manual. Specification p. 2; electrical parts lists pp. 10–11; cabinet parts list p. 12; peripheral schematic p. 23; ALT386SX schematics pp. 24–26.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 Pawel Pieczul, "Amstrad ALT-386SX", oldcrap.org, 24 August 2020, with readers' comments to 2024. Retrieved 2026-10-01. The PSU recap, the configuration switches, the SIMM wiring, battery-leak repair, and further faults and fixes reported by owners in the comments.
  3. ↑ Bibliothèque nationale de France, Collection Charles Cros no. 1008, ALT-286 photograph 15 of 26 (rating label), Wikimedia Commons. Retrieved 2026-10-01.
  4. ↑ Bibliothèque nationale de France, Collection Charles Cros no. 1008, ALT-286 photograph 18 of 26 (memory bay), Wikimedia Commons. Retrieved 2026-10-01.


Retrieved from "https://wiki.retrotechcollection.com/index.php?title=Amstrad_ALT-386SX_Troubleshooting_Guide&oldid=21361"