Restoring 486 pc from the junkyard (or 486 build #1)

Working on another PC from junkyard.

Page with Chaintech motherboard support information and bios updates.

Motherboard

Manufacture: Chaintech 4SPI
Chipset: SiS 85C496/7
BIOS String: 02/16/95-SiS-496-497/A/B-2A4IBC31-B2
BIOS Version: Award v4.50G

Y2K

Strange thing. After setting the date and time in bios and with a new CMOS battery I have noticed that after restart yar is set to 2094. So either it is some kind of BIOS y2k bug or issue with a motherboard.

Found someone wondering about same issue here.

This Vogon thread was helpful and lead to this page where some flash update was found.

From Chaintech FAQ:

ADDRESSING LARGE CAPACITY HARDDRIVES
One of the most frequently asked questions concerning 486 mainboards is the ability to address large capacity (>1GB) harddrives on these boards. Due to the limitations of the chipsets on these boards it is not possible to directly address these type of harddrives. It is necessary to use third party software such as OnTrack`s DiskManager (or similar) to address the total space of these harddrives. Due to the limitations of the 486 board`s chipsets it is also not possible to fully benefit from advanced features of these harddrives such as higher performance (PIO mode 4, Ultra DMA/33) and other Enhanced IDE`s benefits.

Y2K COMPLIANCE
None of the Chaintech 486 mainboard’s BIOS updates is fully Y2K compliant. In order to address this issue, Chaintech provides a utility, the TSR2000, which should be installed just before the year change 1999-2000. After the year change has passed, you can remove this utility. For more information on this Y2K issue please refer to the  Y2K section on this website.

All Chaintech Mainboards using a BIOS with a datecode of later than June 1996 are 100% Year 2000 Compliant !

See also WWW.AWARD.COM for more information on this issue

All Chaintech Mainboards using a BIOS with a datecode of earlier than June 1996 (mostly 486/386 models) can use our Chaintech TSR2000 software program to become 100% Year 2000 Compliant !

Under Windows 95/98 it is not necessary to use the TSR2000, even when using an older BIOS version.

Bios tools.

Fixes

CPU fan holder was broken, so I have 3d printed mount for a CPU heatsink holder and then hot-glued old fan case to it. Seems to work ok for the moment.

PCU fan was realllllllly noisy, so I have replaced the PSU fan with some other I had, much quieter.

Bios chip. Originaly it used M27C1001 UV-EPROM IC as BIOS ROM. I have tried to burn it with my Mini Pro programmer, but due to voltages it requires, I have failed.

So I have ordered couple of 27SF010 many time programmable Flash IC. It can be used as a direct replacement for M27C1001.

I have flashed it with latest bios for this motherboard that I have found here. It worked perfectly.

Turbo

Turbo button does switch MHz LCD from 100MHz to 16MHz, but turbo LED is always on.

I have tried enabling/disabling turbo using keyboard shortcut CTLR+ALT+- or + (or Shift+Ctrl+Alt++ or -). Turbo LED reacts to keyboard commands and goes on and off. After playing with keyboard, when switching turbo button, turbo LED also reacts. But after restart again, turbo button only changes frequency display, but turbo LED does not react until you send keyboard command. Strange.

So, turbo button reacts only after you send turbo command with keyboard.