Spotted this post. This could be connected to my issue.

What is wrong with my GA-486vs ( Solved ).

You mention EDO RAM (GM71C18163CJ6 is EDO RAM), the motherboard only supports FPM RAM. This would explain your inconsistent results.
Once you have FPM RAM, you might want to put a jumper on position 2-3 to get it running at full speed.
And after that add some cache for a decent performance boost.

Dorunkāku wrote on 2024-08-26, 17:24:

You mention EDO RAM (GM71C18163CJ6 is EDO RAM), the motherboard only supports FPM RAM. This would explain your inconsistent results.
Once you have FPM RAM, you might want to put a jumper on position 2-3 to get it running at full speed.
And after that add some cache for a decent performance boost.

I did suspect the RAM. Thanks for confirming this is likely the issue. I'll order some FPM ram.

Which jumper are you referring to regarding position 2-3?

Also, I note that I have no cache RAM and there are no jumper settings for 0 cache - only a minimum of 64k. I have it set at 64k with JP1, 2 and 3 set to OFF. Do I need cache installed? Should my settings work fine with 0 cache installed?

Thank you!

jarcher1701 wrote on 2024-08-26, 16:46:

The two memory sticks still in the board are labelled as 'GM71C18163CJ6'. These are Hynix and I suspect also EDO ram. Could EDO ram be the cause of the weird CPU identification problem?

Yes, as mentioned above this motherboard this board does not support EDO RAM and neither do most other 486 boards except later ones (usually PCI ones). It is most likely the cause of your problem.

jarcher1701 wrote on 2024-08-26, 16:46:

I did notice that the https://dosdays.co.uk/media/gigabyte/ga-486vs.pdf suggests "All of the items or discription regarding DX4 CPU in this manual don't support for those motherboards without 3.3V regurator. How do I know if there's a regulator or not?

There is a regulator, it's the LT1085CT chip near the CPU.

jarcher1701 wrote on 2024-08-26, 17:46:

Also, I note that I have no cache RAM and there are no jumper settings for 0 cache - only a minimum of 64k. I have it set at 64k with JP1, 2 and 3 set to OFF. Do I need cache installed? Should my settings work fine with 0 cache installed?

When you have no cache what you do is set any value with the jumpers (64k, 128k or 256k) and then make sure to set the "External cache" or "L2 cache" option in the BIOS to "Disabled". The BIOS won't enable cache until the end of the POST so it doesn't matter what value is set with the jumpers if you disable it in the BIOS.

I wanted to say: put a jumper on position 2-3 of J3 to make it run at full speed.

I have the same motherboard and had the same problem.
I think this motherboard only supports 5v CPU's
So I could only get the 486dx-33 thru 66 to work
also had a problem with adding cache. I could only get 64kb of motherboard cache to register.
an Intel over drive CPU should work.

Anyways, If you want to get it to work.
Just forget about motherboard cache and set the jumpers for 5v 486dx-33 and add and intel over drive CPU
486dx4-75
486dx4-100
Pentium over drive 83mhz

I would just get the Pentium Over drive.

Intel486dx33 wrote on 2024-08-27, 00:50:

I have the same motherboard and had the same problem. I think this motherboard only supports 5v CPU's So I could only get the 4 […]
Show full quote

I have the same motherboard and had the same problem.
I think this motherboard only supports 5v CPU's
So I could only get the 486dx-33 thru 66 to work
also had a problem with adding cache. I could only get 64kb of motherboard cache to register.
an Intel over drive CPU should work.

Anyways, If you want to get it to work.
Just forget about motherboard cache and set the jumpers for 5v 486dx-33 and add and intel over drive CPU
486dx-75
486dx-100
Pentium over drive 83mhz

I would just get the Pentium Over drive.

I have seen a few of your posts about this board. It seems you had a few issues with DX4 CPUs as well.

Do you think you had the version without a voltage regulator? It's the regulator that allows for 5V/3.3V switching. The board manual suggests that DX4 100s are fully supported with a regulator.

I did note that I have a Revision 6 and most manuals online seem to be 8a or 8b. I'm not sure how this affects compatibility with DX4-100 chips.

Dorunkāku wrote on 2024-08-26, 17:24:

You mention EDO RAM (GM71C18163CJ6 is EDO RAM), the motherboard only supports FPM RAM. This would explain your inconsistent results.
Once you have FPM RAM, you might want to put a jumper on position 2-3 to get it running at full speed.
And after that add some cache for a decent performance boost.

FPM RAM arrived. The board and CPU is now working fine.

Adding a jumper to J3 2-3 set the MHz correctly to 100. It took me a moment to realise that these are the turbo button pins - which explains the 48Mhz default without turbo enabled. Thanks!

I have no cache although I might be able to salvage from another board. Is there a good place to get this from - aside from eBay? Thanks!

Also, does anyone know if this board would support AMD 5x86 chips? The voltage is slightly different to the 3.3v setting of this board - 3.45. Do only later boards support this chip? Thanks!

You may use a interposer socket that drops power to 3.3 Volt. But...
Your 5x86 will run in write-through mode (L1-cache).
This will result in so much power being lost that you will be disappointed with the results.

It also looks like your BIOS won't setup the parameters (waitstates) right for your CPU.
And... where are your L2 cache modules?

jarcher1701 wrote on 2024-08-29, 18:56:

Also, does anyone know if this board would support AMD 5x86 chips? The voltage is slightly different to the 3.3v setting of this board - 3.45. Do only later boards support this chip? Thanks!

Well, your board has no support in the BIOS for that CPU or even any WB CPU's, it misses the core voltage support and it isn't mentioned in the manual. So, support...no.

Will it work? Yes I think so. You already got the AMD WB DX 100 working without it being supported. The lack of BIOS support for the 5x86 will cause it to be misidentified during POST, but that is just a cosmetic thing that can be fixed by a BIOS update.
The core voltage being 0.15 volt to low is insignificant.

According to the manual putting a jumper on pin 3-4 of JP24 will set 2x multiplier which will putthe 5x86 in 4x mode.

As for the cache: you are going to put 30 year old chips in 30 year old sockets. You might want to use contactspray or deoxit. Make sure the pins are straight and line up with the holes in the sockets. I recommend you go for the 8* 32Kx8 DATA plus 32Kx8 TAG option as shown here. So get 9 32Kx8 15ns chips (Maybe order some spares?). This will give you 256KB of L2 cache. Get them from Ebay or a reputable recycler. example

Good luck!

Dorunkāku wrote on 2024-08-30, 01:18:

Well, your board has no support in the BIOS for that CPU or even any WB CPU's, it misses the core voltage support and it isn't m […]
Show full quote

jarcher1701 wrote on 2024-08-29, 18:56:

Also, does anyone know if this board would support AMD 5x86 chips? The voltage is slightly different to the 3.3v setting of this board - 3.45. Do only later boards support this chip? Thanks!

Well, your board has no support in the BIOS for that CPU or even any WB CPU's, it misses the core voltage support and it isn't mentioned in the manual. So, support...no.

Will it work? Yes I think so. You already got the AMD WB DX 100 working without it being supported. The lack of BIOS support for the 5x86 will cause it to be misidentified during POST, but that is just a cosmetic thing that can be fixed by a BIOS update.
The core voltage being 0.15 volt to low is insignificant.

According to the manual putting a jumper on pin 3-4 of JP24 will set 2x multiplier which will putthe 5x86 in 4x mode.

As for the cache: you are going to put 30 year old chips in 30 year old sockets. You might want to use contactspray or deoxit. Make sure the pins are straight and line up with the holes in the sockets. I recommend you go for the 8* 32Kx8 DATA plus 32Kx8 TAG option as shown here. So get 9 32Kx8 15ns chips (Maybe order some spares?). This will give you 256KB of L2 cache. Get them from Ebay or a reputable recycler. example

Good luck!

Great. Thanks for the advice.

The current AMD 486 DX4100 is being identified as a "DX4-S". I assume it should say "AMD 486 DX4-100" or something similar - but the Bios doesn't recognise it, right. The same will be the case for a 5x86, as you say. How would I update the bios? Would I flash a new EMPROM. Are these Award Bios images freely available somewhere?

Thanks for the cache advice. I'll look into it.

jarcher1701 wrote on 2024-08-30, 21:36:

The current AMD 486 DX4100 is being identified as a "DX4-S". I assume it should say "AMD 486 DX4-100" or something similar - but the Bios doesn't recognise it, right. The same will be the case for a 5x86, as you say. How would I update the bios? Would I flash a new EMPROM. Are these Award Bios images freely available somewhere?

Hi jarcher1701,

The BIOS on this board is in an EPROM chip and can’t be flashed in the board. I know only of a few late 486 PCI boards that had a Flash EEPROM chip and could use a Flashing Utility, but all other 486's like your GA-486VS need an external programmer to program the BIOS chip. Luckily the EPROM is in a socket and can be easily replaced.

Your original 64KB 28-pin DIP BIOS chip is probably a 27C512 or equivalent UV-EPROM. These chips need to be erased by UV-light, hence the quarts window on top, before you can re program them.
So it is much easier to buy a new (E)EPROM to program the updated BIOS and keep the original EPROM as backup.

For these BIOS experiments I advise to use a Winbond W27C512 EEPROM. These are compatible with 27C512 UV-EPROMs but can be electrically erased for re-programming. No hassle with UV-light anymore.
But you still need an external programmer to program the BIOS in the (E)EPROM chip, or find somebody to do this for you. 😉

For proper AMD 486DX4 and Am5x86 support, you indeed need a BIOS update.
Did you see this thread from 2 years ago?
160mhz CPU on VLB Motherboard ?
I adapted an 11/28/95 SiS471 BIOS for the GA-486VS and you can download this GA-486VS Rev. J.1 BIOS from my second reply in this thread.
This BIOS supports all socket 3 CPUs, including the Cyrix 5x86 and Am5x86 in L1 cache WB and x4 multiplier mode. It’s also free of the year 2094 and 2GB HDD display limit bugs and supports drives up to 8GiB.

Further down in this thread, TheMobRules uploaded a Rev. J.2 version of this BIOS with a tweak that increases memory performance considerably.
I recommend this Rev. J.2 BIOS for your GA-486VS upgrade.

Cheers, Jan

Chkcpu wrote on 2024-09-01, 17:55:

Hi jarcher1701, […]
Show full quote

jarcher1701 wrote on 2024-08-30, 21:36:

The current AMD 486 DX4100 is being identified as a "DX4-S". I assume it should say "AMD 486 DX4-100" or something similar - but the Bios doesn't recognise it, right. The same will be the case for a 5x86, as you say. How would I update the bios? Would I flash a new EMPROM. Are these Award Bios images freely available somewhere?

Hi jarcher1701,

The BIOS on this board is in an EPROM chip and can’t be flashed in the board. I know only of a few late 486 PCI boards that had a Flash EEPROM chip and could use a Flashing Utility, but all other 486's like your GA-486VS need an external programmer to program the BIOS chip. Luckily the EPROM is in a socket and can be easily replaced.

Your original 64KB 28-pin DIP BIOS chip is probably a 27C512 or equivalent UV-EPROM. These chips need to be erased by UV-light, hence the quarts window on top, before you can re program them.
So it is much easier to buy a new (E)EPROM to program the updated BIOS and keep the original EPROM as backup.

For these BIOS experiments I advise to use a Winbond W27C512 EEPROM. These are compatible with 27C512 UV-EPROMs but can be electrically erased for re-programming. No hassle with UV-light anymore.
But you still need an external programmer to program the BIOS in the (E)EPROM chip, or find somebody to do this for you. 😉

For proper AMD 486DX4 and Am5x86 support, you indeed need a BIOS update.
Did you see this thread from 2 years ago?
160mhz CPU on VLB Motherboard ?
I adapted an 11/28/95 SiS471 BIOS for the GA-486VS and you can download this GA-486VS Rev. J.1 BIOS from my second reply in this thread.
This BIOS supports all socket 3 CPUs, including the Cyrix 5x86 and Am5x86 in L1 cache WB and x4 multiplier mode. It’s also free of the year 2094 and 2GB HDD display limit bugs and supports drives up to 8GiB.

Further down in this thread, TheMobRules uploaded a Rev. J.2 version of this BIOS with a tweak that increases memory performance considerably.
I recommend this Rev. J.2 BIOS for your GA-486VS upgrade.

Cheers, Jan

Thank you so much. That's really helpful.