jakethompson1 wrote on 2025-08-13, 01:30:

newbie1 wrote on 2025-08-13, 01:14:

Wonder if anyone can help me. I have an Ebay ASUS VL/I-486SV2G motherboard that I'm trying to setup. It has an Award BIOS chip v4.50G. I can boot into the BIOS settings OK and move around the various setup options. But when I went install DOS 6.22 I got an error "can't enable A20", and I also lost the keyboard control ...no response from the keyboard and the same from 2 other keyboards. So I tried a spare AMI 486 BIOS chip in the socket and was actually able to use the keyboard outside of the BIOS setup screens. I can't continue to use that BIOS chip because it's meant for a different chipset, but it seems clear that the problem is with the Award BIOS chip the board came with. Can anyone tell me what my options are to get this board working. Any help much appreciated.

If the CPU is jumpered so that WB/WT# puts it in L1 write-back mode, but the other control lines related to L1 write back aren't jumpered correctly or wired correctly on the board, it can cause bizarre symptoms like that. Is yours a rev 1.x? See ASUS VL/I-486SV2G(X4) REV. 1.8 conversion and jumpers guide

Yes it's a rev 1.4. I'll check the link you sent. Thanks for your help.

The guide seems to be about preparing the board for an Am586. I'm just using a plain old i486 dx2/66. I downloaded a manual from Asus for rev 1.7 and also another from Retroweb for rev 1.0, but neither are a perfect match for the jumpers on my board, so I just followed the silk screened settings on the board for cpu type, bus speed etc., and according to that it's setup for a 486-66. Should I look at replacing the BIOS chip or burning a new one?

It's a plain &E 486DX2-66 not &EW on the label, right?

If so I agree, it should "just work," don't have any ideas other than (1) the previous owner put the wrong BIOS on, or (2) something is wrong with the KBC since it uses a discrete one.

It wouldn't just be bit-rot with an old BIOS chip that worked originally and no longer does, as the BIOS code is protected by a checksum.

Yes, just a very plain 486DX2-66. Not quite sure what the '&EW' was in your message, but anyway that wasn't written on it.

Retroweb has a copy of the original BIOS that I've downloaded and I'm trying to find a version of awdflash that will work with the eprom my bios is on. Seems to be an obscure one. So anyway I thought I would try to flash the bios again. Any thoughts?

About wrong BIOS... Long time ago I had a video card which was flashed the wrong BIOS by a previous owner. A Riva 128 made by MIRO with additional connectors for VIVO was flashed with the BIOS of ELSA Victory Erazor. Overall, things were ok unless using higher resolution modes. Found the proper BIOS for the card.
Many years ago several friends bricked their PCs by flashing the wrong BIOS; I managed to fix that.

newbie1 wrote on 2025-08-13, 03:48:

Yes, just a very plain 486DX2-66. Not quite sure what the '&EW' was in your message, but anyway that wasn't written on it.

Retroweb has a copy of the original BIOS that I've downloaded and I'm trying to find a version of awdflash that will work with the eprom my bios is on. Seems to be an obscure one. So anyway I thought I would try to flash the bios again. Any thoughts?

You cannot flash the BIOS chip on that motherboard with command line tools like awdflash. Like most boards of that era, you need to erase the chip with UV light and write the new BIOS with an EPROM programmer like the TL866 or similar (or just write the BIOS to a new chip and replace the old one if you don't want to erase it, but you still need a programmer).

Thanks for that info. I'll look into the TL866. I'd probably go for just writing it to a new chip, but the markings on the BIOS chip are STM M27C512-15F1. Do I need to find the exact same chip type to write the new BIOS or is there an equivalent? Are the programmers fairly easy to use?

newbie1 wrote on 2025-08-13, 13:16:

Thanks for that info. I'll look into the TL866. I'd probably go for just writing it to a new chip, but the markings on the BIOS chip are STM M27C512-15F1. Do I need to find the exact same chip type to write the new BIOS or is there an equivalent? Are the programmers fairly easy to use?

Yes, the software of these programmers is really easy to use, either the old TL866 or its newer variant the T48 are solid choices. For the chip, any 27C512 will work fine (150ns or less), people usually recommend the Winbond W27C512 since it is electrically erasable, meaning you don't need UV light to erase it.