386SX-20 clone build log

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386SX-20 clone build log

Postby Washerman » Sat Jan 09, 2016 1:27 pm

TL;DR version: I'm building a replica of my first IBM-compatible 386SX-20. Now skip to photos :D

Long version: Back in 1991, my family's computer was the very outdated Apple II (and a clone at that). By that time I'd had 2 years of using Macs, and badly wanted to play the cool games my friends with IBM-compatible machines had.

Eventually I was told to pick a reasonably priced computer. My hardware budget could afford at best a tower containing a 386SX 20MHz, with 4MB RAM, an 80MB WD Caviar hard disk, Tseng 1MB video card and 14" Super VGA monitor. The CPU was an AMD, and I had no spare cash for a 387SX. Floppies were 5.25" Teac and 3.5" Panasonic. The Windows 3.0 supplied came with the mouse, a Z-Nix bundle. To get to this point I'd spent ages poring over specs and builds based on Australian PC User magazines, the Trading Post/Sydney Morning Herald advertisements, and any scrap of computer media I could find. The machine was put together by "L+C Computers" in Parramatta, who had the best prices at the time, but are long since gone.

Given how much time I'd spent on this machine, it's a wonder that 10 years later it was found to be taking up too much room, served no purpose, and was put on the kerb (no doubt the scrappers got it first). In fact at the same time the Apple II clone went as well. Everything was still pretty mint, no rust or yellowing. How I miss those machines!

Fast forward 15 years, and the hunt to build as close a replica as possible to the 386SX was on. I wasn't getting anywhere until one day I came across an AT clone with the same faceplate (seems to be a common one). Some time during its life this machine was built into a 486/DX4 100, with 64MB RAM (4x 16MB 30pin SIMMs), Tseng 4000/W32i VLB, and Adaptec 1542 SCSI. Basically that means I'm downgrading this machine! :geek: Managed to get the whole thing free as part of a mass cleanout. The Seagate drive in this one has died, but that's no problem. The only differences I can pick so far are that it has a rocker power switch (mine had a round push button), ventilation holes in the bottom of the case (original was solid), the molded faux 3.5" slot cover (why was this a thing? I have flat ones to replace it) and the rear backplane can be removed (original was one piece or welded). This is missing a top cover, but I've got an AT donor case for that. The shots don't show it, but the inside of the case is rusted at the front corner.

386SX20 Before
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386SX20 AT PSU
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386SX20 PSU build date
_DSC1883.JPG (669.76 KiB) Viewed 3754 times

386SX inside cover
_DSC1907.JPG (468.82 KiB) Viewed 3754 times

386SX clean fascia
_DSC1939.JPG (428.18 KiB) Viewed 3754 times

The 486 configuration does boot, and so I'll use that in a desktop machine, to replace a 486DX2/66. The board has some minor battery damage, but a PO has modded an off-board CR2032 solution, which is very thoughtful.

386SX 486 board
_DSC1920.JPG (997.12 KiB) Viewed 3754 times

386SX 486 battery mod
_DSC1897.JPG (586.89 KiB) Viewed 3754 times

To match the old specs, I've purchased a 386SX20 board from Russia (Intel chip), used 4MB RAM from my parts stash, had a Tseng 1MB card sent by dacow (thanks! :D), bought 2x 80MB WD Caviar 280s (these are fragile units), and will reuse the Teac 5.25" (mine had a green light like this one), and just cleaned up a couple of Panasonic 3.5"s. Also bought the same old mouse, a Honeywell AT kb (one of these was hooked up to the original in its life). Have DOS 5.0, Windows 3.0 ready to go as well.

386SX motherboard test
_DSC1815.JPG (1.22 MiB) Viewed 3754 times

386SX test run
_DSC1814.JPG (805.86 KiB) Viewed 3754 times

Fired up the old combo with an Eagle IDE controller (probably Acer-based, can't recall what the original had), and it works! Played some Star Goose, Omega Chess, and tried Wolf3D but didn't get far with that. Contents of the HD haven't been touched since 1992!!! Seems slower than I remember, but then back in the day I was in awe of having an IBM-compatible, so that probably explains it.

To-do list:

  1. Fix rust on the case, and prime/spray
  2. Install 386SX setup into case
  3. Back up 80MB drive
  4. Wipe and install DOS/Windows/Office
  5. Install Mediavision Pro 3D
  6. Buy Toshiba XM-3501B 4x CD-ROM - this was fitted to the computer in 1994

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Re: 386SX-20 clone build log

Postby dacow » Sat Jan 09, 2016 5:48 pm

Love the faux 3.5" plates, no idea who thought they were a good idea though. What happened with Wolf3D? Did you have an issue with it or you just didn't play it much?

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Re: 386SX-20 clone build log

Postby Washerman » Sat Jan 09, 2016 7:47 pm

Ah, I only had a little time, so fired it up, and tied to load a save game for fun - it crashed the game, and I didn't go back to start a new game. I've got a fair few games to run on the SX, so once it's built up, the fun will begin :D

One point on this build, though, I won't be looking for a 14" CRT, unless one *accidentally* crosses my path ;)

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Re: 386SX-20 clone build log

Postby mwd » Sun Jan 10, 2016 1:20 pm

Nice machine. That 486 heat sink hack job looks interesting! Is that a DX4/100 overdrive?

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Re: 386SX-20 clone build log

Postby Washerman » Mon Jan 11, 2016 1:08 pm

I was curious about the Borg-looking CPU, but now you mention it I think it is an Overdrive! Seems to have the original heatsink ripped off and replaced with a smaller one. Pics of the OD processor on the 'Net show the components through the heatsink fins. I was previously under the impression it was an AMD. I'll put up some pics of the 486 desktop build when it comes up on the roster ;)

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Re: 386SX-20 clone build log

Postby monaro327 » Mon Jan 11, 2016 3:22 pm

Is a pretty ghetto looking CPU.

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