Tzzantaru wrote on 2025-05-30, 18:41:

Hello again,

So, good news and bad news.

Good news is that I found someone that was kind enough to help me write the new chips. Bad news is that the motherboard is still giving me the cold shoulder.

Hi Tzzantaru,

The plot thickens.

I also asked the person to make a backup of the original chip and also the new chip #1 (that I've tried to blindly write the bios on the board itself by hot swap). I attached both backups, maybe they'll give any kind of idea, although I doubt it.

Well, these BIOS dumps actually revealed a lot!

To start with the backup of the original chip, at first glance the BIOS looked completely scrambled but the bootblock, including the decompression engine, was intact. At closer inspection I found 16KB blocks that held a correct section of a compressed module, but at the wrong place. Other 16KB blocks appeared to be cleared/empty.
Checking the backup from the hotflash, the scrambling was even worse.

The backup of the original flashchip represents the state of the BIOS after your last blind bootblock recovery attempt.
On a 128KB Award BIOS like yours, the start of the compressed main BIOS module (original.tmp) should be at offset 0000h in the BIOS file. However, I found the first 16KB of this module at offset 4000h!! So I’m beginning to think you have a stuck address-line on your board!

This would also explain the lack of video from your ISA card, because when the bootblock recovery code try’s to initialize the video card by calling its initialization routine, it first checks for the AA55h Video ROM signature at address C000:0000h. If it can’t find this signature at this address, it sends out a beep code and skips the video init.
With a stuck address line, this check will always fail because the video ROM presence check is send to the wrong address!
A stuck address line would also prevent a correctly programmed BIOS from functioning.

That the whole bootblock was still intact can also be explained by the fact that Awdflash.exe normally keeps this section of the flashchip write protected. Only when it detects that the bootblock needs to be updated as well, it will write to this flashchip section.

So, where to look for a suspect address line? Although the BIOS ROM and ISA bus are connected to the Southbridge, the RAM is connect to the Northbridge. My bet would be a faulty connection or shortcircuit near or in the RAM slots, or a damaged trace to the northbridge.

I hope this helps you further,
Jan

Hi again,

Maybe I’m double guessing myself, but after my previous message I’ve been looking further into this possible stuck address line issue.

Seeing that the Southbridge controls the BIOS ROM, ISA bus, and IDE ports from a common address and data bus (probably via buffers), I’ve been hypothesizing if the stuck or floating address line could be here.
The Southbridge is connected to the Northbridge via the PCI bus, so their address and data lines are physically separated. Although a stuck address line on the Northbridge’s memory bus could still be translated over the PCI bus to the Southbridge, I now think it is more likely that the problem is actually on the Southbridge’s address bus to the BIOS and ISA bus.

Because I found a 16KB shift in addressing a section of the BIOS, the most suspect address line is A14. This is pin 21 on the VT82C586B, pin 29 on the BIOS chip, and pin A17 on the ISA bus https://en.wikipedia.org/wiki/Industry_Standard_Architecture
Maybe you can find a broken connection or shortcircuit with another line here.

Note that address line A14 must be high when accessing the top 16KB of the BIOS. This is where the bootblock is so addressing this part of the BIOS is not affected if A14 is stuck high.

I’m curious what you will find.
Cheers, Jan

Hello Jan

Thank you for the reply.

I have read both posts and I'm now trying to understand everything and make some notes of the things I need to check. First of all I'm not really that competent in this department but I'm trying to research and read and educate myself on the matter.
Fortunately I have the vast internet at my disposal and lately Chat GPT does an awesome job of explaining things 😀)
Unfortunately I only own a multimeter and though I know my way around it to check stuff, apparently I also need an oscilloscope for what I need to verify going forward (or at least find someone with one and lend it 😁).

I did have a little time at work today to make a list of address lines between the bios chip and northbridge and/or southbridge and/or ISA slot but since I need an oscilloscope for the majority of tests, this is going to take a while.

One thing I'm trying to understand now. The first new chip that I've tried to hot swap and flash was empty but somehow the board was able to write the bootblock part perfectly and then mess the rest of the bios files. Why?
I'm still trying to figure out what handles the write process for the whole flashing. What manages the file transfer between the floppy and the chip?

Also, I'm 99% sure that there is no physical damage to the board/traces as I've always took care of the components. Never scratched the board, never hit it with anything, never dropped anything on it. I was always careful when removing it from the case and putting it in storage. There are no caps that leaked so there's no damage from that.
I never damaged any board that I handled so my intuition would say that the problem is a component that's just given up due to age. Problem is I need to find out which one and hope that it's not the northbridge/southbridge as I don't think I could find a replacement for them and it's going to cost a truckload of money to replace.

I appreciate your answers and advices

Thank you