Amstrad ALT-386SX


Amstrad User Group

There is no Service Manual available on the Internet. If you have one and want to share, please let me know.




Somehow I forgot to make pictures of the motherboard. So this is only front of a dirty board after dismantling the machine. Now the computer is all assembled.

BIOS entry key is F2 during boot or CTRL-ALT-S from DOS prompt.

Power Supply

Rubycon RPS-07

ROM/RAM Module

Graphics Card

ISA Interposer Board

Hard Disk Drive

80 MB Sony SRD3080C-50. HDD Type in BIOS is 24.

Floppy Disk Drive


Display/Keyboard Adapter Board

LED Panels

Display & Backlight Inverter Board


Epson EG9005-F-LS-2




Fixing ALT-386SX

Phoenix BIOS Beep Codes

When BIOS boots, it reports errors of the power-on self tests in a form of audio beeps on the built-in speaker. The meaning of the error code can be found on the BIOS Central web page.

Checking the Configuration Switches

There are two sets of switches at the back of the computer. For first boot it is probably best to set the smallest memory size and internal display. When there is less memory available than configured, BIOS will report a beep error code. OFF = switch is UP, ON = switch is DOWN.

SW1SW2SW3Memory Size
SW4Page modeAlways ON
SW5Wait statesAlways OFF
SW6Clock8 Mhz16 Mhz
SW9PipelineAlways ON
SW10Drive B: TypeAlways OFF

Recapping Power Supply

All electrolytic capacitors used in the Rubycon power supply are of poor quality and they all leaked. The effect was that the output voltages were much lower than required. Replacing the capacitors restored the correct voltage levels.

Checking SIMM Connectivity

When there are memory problem reported by the BIOS, it makes sense to check the SIMM connectivity to the chipset, especially when there was a battery leak that could have damaged the PCB traces.

SIMM modules are organised in Columns (0, 1 – also called banks) and Rows (1, 2).

Stored data bits are divided between rows: bits 0-7 are stored in row 1 and bits 8-15 in row 2. Therefore two SIMMs must always be inserted into row 1 and 2. Column 0 is used as a lower memory location and must be always populated with SIMMs, as it is used to boot the machine. Column 1 is optional and may be used for a memory extension.

SIMMs are wired to four chips on the motherboard, VL82C202 (Memory Controller), VL82C203 (Address Buffer), VL82C204 (Data Buffer), VL82C205 (Page Mode / Interleave Controller). Some of the signals are connected through a resistor soldered to the bottom side of the ROM/RAM board. If a resistor is present, when checking the connectivity of the traces, please locate and use the connection after the resistor, not at the SIMM.

SIMM Column
Chip Pins
Data Bits 8-15D0-D7*1VL82C204D8-D15
Data Bits 0-7D0-D7*2VL82C204D0-D7
Column Address Strobe/CAS01R337VL82C205CAS0L
Column Address Strobe/CAS02R338VL82C205CAS0H
Column Address Strobe/CAS11R339VL82C205CAS1L
Column Address Strobe/CAS12R340VL82C205CAS1H
Address Bits 0-7A0-A7**R321-R328VL82C203MA0-MA7
Address Bits 8-9A8-A9**R329-R330VL82C202MA8-MA9
Address Bits 10-11A10-A11**n/c
Write Enable/WE0*R331VL82C205RAMWA
Write Enable/WE1*R332VL82C205RAMWB
Data Parity OutQP*1VL82C204MDPOUT0
Data Parity OutQP*2VL82C204MDPOUT1

Pinouts of the chips used in the table above:

Fixing a Battery Leak Damage

Leaking CMOS battery can cause severe damage to the board. It can oxidate and dissolve traces and vias.

The board can be cleaned with vinegar. Vinegar should not be left on the board for too long and can be removed with clean water (possibly with some baking soda added).

In order to fix the traces, the most damaged chips should be removed from the board to reveal more damage to the traces beneath the chips.

Now it is best to use some super fine grade sanding paper to remove the varnish and reveal all the traces.

Making photos of the board and using a paint application to draw multiple colors on top of the traces will tremendously help in checking the connectivity and fixing broken traces.

Traces can be fixed with a special ultra-thin wire. It is possible to solder the wire directly into the vias on the board. The mesh looks messy, but does the job. Before soldering the SMD chips back to the board, use PCB coating varnish to protect the uncovered traces. When all soldering is done, use more coating on all the uncovered traces and soldering points.