Hi marbury, welcome to Vogons!

Recently I had the exact same symptoms on another 486 board, using a Cyrix 486DX2-66 CPU.
This CPU supports L1 cache in Write-Back mode and the problem went away when I used another CPU that has L1 cache Write-Through support only.
Later I found an error in the jumper setting for Cyrix CPUs and now my Cx486DX2 is running happily in WB mode on my board. 😀

Is your Intel 486DX4 a WB version? Should have &EW stamped on top.
If so, try to force the WT mode by closing jumper JC1. This should allow a normal floppy boot when lack of L1 cache WB support by the motherboard or BIOS is the problem.

But if your DX4 has a &E marking, then it is a WT only version and the above solution won’t help.

Good luck,
Jan

marbury wrote on 2023-01-10, 17:42:

Hi, […]
Show full quote

Hi,

I recently obtained a 486 setup

• FIC 486 PIO2 board
• intel 486DX4 100 (iconv=435)
• 64MB RAM
• GPU: S3 Trio64V+
• Floppy: Mitsumi D353M3D (floppy cable is a twisted one)
• Cache ICs: 4 x tmtech 12512A-20k TC3787D 9530

When I start the system and try to boot from the first DOS install disk the following happens in order:

1. POST beep
2. Memory check (OK)
3. primary master found: Clouddisk 2GB
4. Floppy Seek
5. system config table shown with expected data
6. Floppy starts to turn with 2 short head move sounds
7. THE END - Floppy Light stays on

What I have tried so far:

• disable cache in BIOS
• disable cache in BIOS and remove ICs
• switch S3 PCI card for a Trident ISA card
• change CPU voltage between 3.3, 3.45, 3.6V
• change cache amount jumper
• remove and reinstall the CPU
• removed every ram stick and installed each one alone
• removed the GPU and booted without (expected 1fast, 2slow beeps but frozen at same point)
• removed and reinstalled the CPU

Other things:

• when there is no floppy in the drive it complains that there is no bootable disk. When I then insert the boot floppy it freezes after the 2 short seeks
• when I remove the floppy it does not boot
• I tried different things to flash the boot image to a floppy on mac and tried different floppies, too: dd if=image of=/dev/disk6 (without bs, with bs=512, bs=1024, conv=sync) and also balenaEtcher
• I used the dos setup image to install dos in virtual box which worked
• I tested a Win95 boot disk. Same thing.

So I am out of ideas here. I hope you good people have an idea otherwise I am screwed 🙁

Hi,

The CPU is properly cooled?
Do you see 100MHz in the first screen? Just to make sure that it is really external 33MHz. DX4 would also support 50MHz * 2, but that is more difficult.
Did you try to reset all BIOS settings to default?
Do you have a 5 volts cpu to test? DX-33 or DX/2-66 would be best, those are the most compatible CPUs 😀

Chkcpu wrote on 2023-01-10, 18:33:

Is your Intel 486DX4 a WB version? Should have &EW stamped on top. If so, try to force the WT mode by closing jumper JC1. This s […]
Show full quote

Is your Intel 486DX4 a WB version? Should have &EW stamped on top.
If so, try to force the WT mode by closing jumper JC1. This should allow a normal floppy boot when lack of L1 cache WB support by the motherboard or BIOS is the problem.

Good luck,
Jan

Yeah it's an &EW "version" and according to the S-spec number (SK0096) it is a "A80486DX4WB-100"

YOU ... ARE ... MY ... HERO ... this actually worked! So now the DX4 runs in P24D mode (isn't that the P Overdrive?). I would have never suspected that THAT is the solution. I read all spec sheets up and down and was just about to give up ...

I think I love you 😁

Cheers,
Stefan

CoffeeOne wrote on 2023-01-10, 18:41:

Hi, […]
Show full quote

Hi,

The CPU is properly cooled?
Do you see 100MHz in the first screen? Just to make sure that it is really external 33MHz. DX4 would also support 50MHz * 2, but that is more difficult.
Did you try to reset all BIOS settings to default?
Do you have a 5 volts cpu to test? DX-33 or DX/2-66 would be best, those are the most compatible CPUs 😀

Just wanted to answer you as well even though the problem is solved 😀 .. Yeah it's cooled properly and actually was in the x3 setting. Now it's in P24D setting with WT on even though the CPU is listed as WB. Anyway. Thanks for help.

Cheers,
Stefan

Allright, to leave this here in case anyone (or me) needs it again later:

I updated my bios to the latest version 115c701 and now I can boot with the correct jumper settings instead of forcing WT. So it might be that the bios version was just too old. Also 1.15c701 should support the AM5x86-p75 I will get soon

• Bios file used from here: https://theretroweb.com/motherboards/s/fic-48 … -pio2#downloads
• awdflash v5.33 used from here: https://www.wimsbios.com/awardflasher.jsp#gsc.tab=0 (*)

(*) newer version might work as well but I couldn't flash with any 7 or 8 version since it flat-out refused the bios file

Hi Stefan,

Great to hear that my L1 cache WB idea paid off! 😀

I was about to suggest a BIOS update when I saw you today message. Yeah, the VT498G chipset has support for L1 cache WB and I'm glad a BIOS update fixed it.
You choose the version 115c701 BIOS, but have you seen Question about FIC486 PIO2 BIOS?
These 4 BIOSes from April 1996 look the same but are for different board variations.
Just to make sure you picked the right one. 😉

The Am5x86-P75 should work as well with this board and 04/1996 BIOS.

Cheers, Jan

Chkcpu wrote on 2023-01-11, 18:01:

Hi Stefan, […]
Show full quote

Hi Stefan,

Great to hear that my L1 cache WB idea paid off! 😀

I was about to suggest a BIOS update when I saw you today message. Yeah, the VT498G chipset has support for L1 cache WB and I'm glad a BIOS update fixed it.
You choose the version 115c701 BIOS, but have you seen Question about FIC486 PIO2 BIOS?
These 4 BIOSes from April 1996 look the same but are for different board variations.
Just to make sure you picked the right one. 😉

The Am5x86-P75 should work as well with this board and 04/1996 BIOS.

Cheers, Jan

Hey,
that’s a very good point. No I didn’t see that post yet. Thank you. My bios says 106C701 and the logic chip says PC87332VLJ-5. that makes me feel like I did right? For some reason by checking this c701 and all the codes the bios gave me that the 115c701 is the correct one? If I flashed the right one then my research was successful. If I flashed the wrong one then I am just dumb 😉
Flashing a bios always makes me nervous. That did not change in over 30 years.
But my board still hast the y2k bug (according) to this one benchmark tool where I forgot the name. But this tool also told me that my dx4100 is supposed to be an am5x86 P-75. I mean I am waiting for DHL to bring me one but that tool couldn’t know yet 😁
Is there a better 115c701 out there with the y2k fix or is the bench tool just wrong?

Cheers, Stefan

Allright. I think I found the beta bios talked about in the other thread. At least the README there has the same content. The file is: 1175C701. And it's a beta Bios from 1997. I will see if I can flash this. The only gripe I have with the awdflash tool is that it hangs really often after loading the file and I then have to restart the PC. At least I wouldn't know how to exit the tool and try again.

marbury wrote on 2023-01-11, 22:45:

Hey, that’s a very good point. No I didn’t see that post yet. Thank you. My bios says 106C701 and the logic chip says PC87332VLJ […]
Show full quote

Chkcpu wrote on 2023-01-11, 18:01:

Hi Stefan, […]
Show full quote

Hi Stefan,

Great to hear that my L1 cache WB idea paid off! 😀

I was about to suggest a BIOS update when I saw you today message. Yeah, the VT498G chipset has support for L1 cache WB and I'm glad a BIOS update fixed it.
You choose the version 115c701 BIOS, but have you seen Question about FIC486 PIO2 BIOS?
These 4 BIOSes from April 1996 look the same but are for different board variations.
Just to make sure you picked the right one. 😉

The Am5x86-P75 should work as well with this board and 04/1996 BIOS.

Cheers, Jan

Hey,
that’s a very good point. No I didn’t see that post yet. Thank you. My bios says 106C701 and the logic chip says PC87332VLJ-5. that makes me feel like I did right? For some reason by checking this c701 and all the codes the bios gave me that the 115c701 is the correct one? If I flashed the right one then my research was successful. If I flashed the wrong one then I am just dumb 😉
Flashing a bios always makes me nervous. That did not change in over 30 years.
But my board still hast the y2k bug (according) to this one benchmark tool where I forgot the name. But this tool also told me that my dx4100 is supposed to be an am5x86 P-75. I mean I am waiting for DHL to bring me one but that tool couldn’t know yet 😁
Is there a better 115c701 out there with the y2k fix or is the bench tool just wrong?

Cheers, Stefan

Yes, the 115C701 BIOS appears to be the correct one for your 486-PIO2 board.

I’ve looked into this BIOS for known bugs and CPU support, and all looks fine. No Year 2094 bug and proper Am5x86 support. 😀
The supposed y2k bug could be a 31-12-1999 -> 01-01-2000 transition issue, but can be disregarded as we are now living well into the 21th century. 😉

I’ve also tried to check the 1175C701 beta BIOS but all my tools refused to open this BIOS. MODBIN.EXE issued a “Bad table” warning and UNAWARD.EXE couldn’t find the decompression module.
Because others report using the BIOS just fine, this beta BIOS probably is fine. But unless you own an (E)EPROM programmer, I would advise against flashing it and just stay with the 115C701 BIOS.

Jan

Good to know you have managed to resolve the issue. I am currently experiencing the same problem with a VL/I-486SV2GX4 board - it seems to POST fine but then refuses to boot from floppy - I hear 2 short sounds and it hangs there. This thread reminds me I might need to update the BIOS and see what happens 😀

MMaximus wrote on 2023-01-12, 18:42:

Good to know you have managed to resolve the issue. I am currently experiencing the same problem with a VL/I-486SV2GX4 board - it seems to POST fine but then refuses to boot from floppy - I hear 2 short sounds and it hangs there. This thread reminds me I might need to update the BIOS and see what happens 😀

Hi, so you are using a CPU (like Am5x86) in L1 WB mode, too? Which revision of this board do you have? But anyway the latest BIOS revision with the write-back fix is highly recommended for that board.

I'm not sure about the revision, I got this board in a job lot. At the moment I'm using a 486SX33 for troubleshooting purposes 😀 I need to check the revision # (if it's indicated on the PCB) and the BIOS version

MMaximus wrote on 2023-01-12, 19:31:

I'm not sure about the revision, I got this board in a job lot. At the moment I'm using a 486SX33 for troubleshooting purposes 😀 I need to check the revision # (if it's indicated on the PCB) and the BIOS version

Update helped a lot here. I still suffer the occasional hangs though and have reverted back to WT until the two 5x86‘s have arrived that I have ordered. Then I will try again and see. Maybe the CPU is not as fresh as advertised. Seller said the board/CPU have been tested but I bet he just switched it on and when the POST happens he was fine with it. The initial jumper config was far from working. Anyway got a brand new old stock AT case today, the 52x CDRW works and tomorrow I get a new old stock serial mouse. Then the build is done yeah. Maybe I should sell it for a grand and build another 😁

Chkcpu wrote on 2023-01-12, 16:14:

Yes, the 115C701 BIOS appears to be the correct one for your 486-PIO2 board. […]
Show full quote

marbury wrote on 2023-01-11, 22:45:

Hey, that’s a very good point. No I didn’t see that post yet. Thank you. My bios says 106C701 and the logic chip says PC87332VLJ […]
Show full quote

Chkcpu wrote on 2023-01-11, 18:01:

Hi Stefan, […]
Show full quote

Hi Stefan,

Great to hear that my L1 cache WB idea paid off! 😀

I was about to suggest a BIOS update when I saw you today message. Yeah, the VT498G chipset has support for L1 cache WB and I'm glad a BIOS update fixed it.
You choose the version 115c701 BIOS, but have you seen Question about FIC486 PIO2 BIOS?
These 4 BIOSes from April 1996 look the same but are for different board variations.
Just to make sure you picked the right one. 😉

The Am5x86-P75 should work as well with this board and 04/1996 BIOS.

Cheers, Jan

Hey,
that’s a very good point. No I didn’t see that post yet. Thank you. My bios says 106C701 and the logic chip says PC87332VLJ-5. that makes me feel like I did right? For some reason by checking this c701 and all the codes the bios gave me that the 115c701 is the correct one? If I flashed the right one then my research was successful. If I flashed the wrong one then I am just dumb 😉
Flashing a bios always makes me nervous. That did not change in over 30 years.
But my board still hast the y2k bug (according) to this one benchmark tool where I forgot the name. But this tool also told me that my dx4100 is supposed to be an am5x86 P-75. I mean I am waiting for DHL to bring me one but that tool couldn’t know yet 😁
Is there a better 115c701 out there with the y2k fix or is the bench tool just wrong?

Cheers, Stefan

Yes, the 115C701 BIOS appears to be the correct one for your 486-PIO2 board.

I’ve looked into this BIOS for known bugs and CPU support, and all looks fine. No Year 2094 bug and proper Am5x86 support. 😀
The supposed y2k bug could be a 31-12-1999 -> 01-01-2000 transition issue, but can be disregarded as we are now living well into the 21th century. 😉

I’ve also tried to check the 1175C701 beta BIOS but all my tools refused to open this BIOS. MODBIN.EXE issued a “Bad table” warning and UNAWARD.EXE couldn’t find the decompression module.
Because others report using the BIOS just fine, this beta BIOS probably is fine. But unless you own an (E)EPROM programmer, I would advise against flashing it and just stay with the 115C701 BIOS.

Jan

The borked image might be the reason awdflash crashes then. I suspected something like this and wouldn’t have flashed it anyway. Yes it’s a transition error. It’s set to 2023 just fine. But perfectionist me would have liked to get rid of that error as well. Anyway. Whenever you are in Munich you have earned yourself a coffee 😉

Stefan

CoffeeOne wrote on 2023-01-12, 19:17:

MMaximus wrote on 2023-01-12, 18:42:

Good to know you have managed to resolve the issue. I am currently experiencing the same problem with a VL/I-486SV2GX4 board - it seems to POST fine but then refuses to boot from floppy - I hear 2 short sounds and it hangs there. This thread reminds me I might need to update the BIOS and see what happens 😀

Hi, so you are using a CPU (like Am5x86) in L1 WB mode, too? Which revision of this board do you have? But anyway the latest BIOS revision with the write-back fix is highly recommended for that board.

I can confirm my board is rev 2.0 - I've just updated the BIOS to the latest ​one (VL/I-486SV2GX4 Beta BIOS 0402.001) sourced on the philscomputerlab website. I've doubled checked every jumper setting and they all seem correct, but the system still hangs when trying to boot from floppy 🤔

MMaximus wrote on 2023-01-13, 12:40:

CoffeeOne wrote on 2023-01-12, 19:17:

MMaximus wrote on 2023-01-12, 18:42:

Good to know you have managed to resolve the issue. I am currently experiencing the same problem with a VL/I-486SV2GX4 board - it seems to POST fine but then refuses to boot from floppy - I hear 2 short sounds and it hangs there. This thread reminds me I might need to update the BIOS and see what happens 😀

Hi, so you are using a CPU (like Am5x86) in L1 WB mode, too? Which revision of this board do you have? But anyway the latest BIOS revision with the write-back fix is highly recommended for that board.

I can confirm my board is rev 2.0 - I've just updated the BIOS to the latest ​one (VL/I-486SV2GX4 Beta BIOS 0402.001) sourced on the philscomputerlab website. I've doubled checked every jumper setting and they all seem correct, but the system still hangs when trying to boot from floppy 🤔

Beta BIOS 0402.001 is NOT the version with the write back fix, but it 's not related to your floppy problem.
I guess your jumper settings are wrong. Do not forget to set JP5 and JP6.

MMaximus wrote on 2023-01-13, 12:40:

CoffeeOne wrote on 2023-01-12, 19:17:

MMaximus wrote on 2023-01-12, 18:42:

Good to know you have managed to resolve the issue. I am currently experiencing the same problem with a VL/I-486SV2GX4 board - it seems to POST fine but then refuses to boot from floppy - I hear 2 short sounds and it hangs there. This thread reminds me I might need to update the BIOS and see what happens 😀

Hi, so you are using a CPU (like Am5x86) in L1 WB mode, too? Which revision of this board do you have? But anyway the latest BIOS revision with the write-back fix is highly recommended for that board.

I can confirm my board is rev 2.0 - I've just updated the BIOS to the latest ​one (VL/I-486SV2GX4 Beta BIOS 0402.001) sourced on the philscomputerlab website. I've doubled checked every jumper setting and they all seem correct, but the system still hangs when trying to boot from floppy 🤔

Hello,

Did you give up on this topic?

CoffeeOne wrote on 2023-01-29, 21:32:

MMaximus wrote on 2023-01-13, 12:40:

CoffeeOne wrote on 2023-01-12, 19:17:

Hi, so you are using a CPU (like Am5x86) in L1 WB mode, too? Which revision of this board do you have? But anyway the latest BIOS revision with the write-back fix is highly recommended for that board.

I can confirm my board is rev 2.0 - I've just updated the BIOS to the latest ​one (VL/I-486SV2GX4 Beta BIOS 0402.001) sourced on the philscomputerlab website. I've doubled checked every jumper setting and they all seem correct, but the system still hangs when trying to boot from floppy 🤔

Hello,

Did you give up on this topic?

Thanks for checking - I actually haven't managed to resolve the issue even though all the jumper settings seem correct to me. Maybe I could upload a picture of the board if you don't mind checking it, in case you could see something I haven't noticed?

MMaximus wrote on 2023-01-30, 17:54:

CoffeeOne wrote on 2023-01-29, 21:32:

MMaximus wrote on 2023-01-13, 12:40:

I can confirm my board is rev 2.0 - I've just updated the BIOS to the latest ​one (VL/I-486SV2GX4 Beta BIOS 0402.001) sourced on the philscomputerlab website. I've doubled checked every jumper setting and they all seem correct, but the system still hangs when trying to boot from floppy 🤔

Hello,

Did you give up on this topic?

Thanks for checking - I actually haven't managed to resolve the issue even though all the jumper settings seem correct to me. Maybe I could upload a picture of the board if you don't mind checking it, in case you could see something I haven't noticed?

Yes, you can upload a good picture of your board.