It looks like my board with an AMD586dx5/133 is configured at "p24d/t"

Id question if your board supports the 586 at its native 133mhz at all. You couldn't even get it to post as a 100mhz?

I know some boards will take the chip but not fully get it to it's rated speed.

That bios is 1993/94. Amd586 was 95'.
I don't think iv seen many VLB 586s. Most are on PCI boards that where made around the time it cameout.

Tried reducing multiplier from "33/66/100" setting to 25MHz setting with rest of jumpers set as AMD 3.3v but no still, stuck at 20 23 on POST card.

SodaSuccubus wrote on 2020-06-03, 21:19:

Id question if your board supports the 586 at its native 133mhz at all. You couldn't even get it to post as a 100mhz? […]
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Id question if your board supports the 586 at its native 133mhz at all. You couldn't even get it to post as a 100mhz?

I know some boards will take the chip but not fully get it to it's rated speed.

That bios is 1993/94. Amd586 was 95'.
I don't think iv seen many VLB 586s. Most are on PCI boards that where made around the time it cameout.

That’s a nice motherboard.
Try jumper-7
P24D
3.3v
Write back
CPU speed = 33x4

Thanks - got a feeling may have tried that but not sure so will re-do.

Just going back to first principles, am I right in thinking this CPU should be set up as a DX2 486 at 3.3v and fed 33MHz? Then it internally multiplies the 33 by 4 to get 133?

My motherboard just clumps 33/66/100 on one jumper setting. Other options are 25, 40/80 and 50. These jumpers aren't included in the guide on what to set for CPUs

Intel486dx33 wrote on 2020-06-03, 21:24:

That’s a nice motherboard. Try jumper-7 P24D 3.3v Write back CPU speed = 33x4 […]
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That’s a nice motherboard.
Try jumper-7
P24D
3.3v
Write back
CPU speed = 33x4

I do wonder if the chip is faulty.
From what I read, even if the motherboard doesnt support it, a 5x86 133 with jumpers set to DX4 100 should just work in that mode? Is that correct?

I have tried the configurations above including the suggestion from Intel486dx33 (thanks btw)
I have also found some other jumper settings online specifically for the V4P895P3/SMT/V5.0 motherboard I am using for the 5x86 133 but the furthest I can get is a 20 23 error on the POST card - lots of the settings crap out far earier at d2 d3.
I tried running the board on the 25, 33 and 40 MHz bus speeds.
My amd 486 DX2 66 works fine (i have remembered to set to 3.3v each time I have the 5x86 in!)

Before I try and return, just wondering if there was anything else I should try?

(suggests motherboad does support http://www.elhvb.com/webhq/models/486vlb3/v4p895v5.htm - mine is the SMT 5.0 revision)

Is there perhaps any BIOS update available for your board?

My Asus PVI-486SP3 didn't want to boot an OS at 133MHz (max. 100MHz) until I updated the BIOS. After that, it also recognized it as being a 5x86 instead of a 486 DX4.

Just been looking into that as your notification came up 😉
Should the chip POST even if it an old BIOS if set as a DX4 100 or would that still likely fail?

Turns out the BIOS is older than the marking on the board would suggest.

Is a V4.0 board bios with ID AMIBIOS ID: 40-2004-428003-00101111-072594-OPTI802-H
The latest seems to be V5.2 with ID AMIBIOS ID: 40-2207-428003-00101111-072594-OPTI802-H

The BIOS is on a 28 DIP package. I can find what I think is the V5.2 file online and looks like is 64kb in size.

I've never programmed an EEPROM before - all previous PCs self flash 😉
Do I just need to get any 64kb dip 28 eeprom and a cheap programmer (that is large enough) from ebay/aliexpress?

Sorry, I forgot to check this topic again.

In my case it did still POST at 133MHz but it failed once the OS wanted to start. It did show the table with system specs but my boot disk didn't load, or it showed the "MS-DOS is starting" text and then the cursor started to move diagonally across the screen.

I have no experience with flashing chips with a programmer. I managed to do it on the machine itself by changing the CPU jumpers so the CPU would run in '3x' speed (because '2x' with the 5x86 makes it go '4x' instead), making it run at 100MHz. That allowed me to boot to DOS, so I could backup and flash the BIOS with Uniflash.

After that I could put the CPU back to '4x' mode and it booted fine. The BIOS then also showed the correct CPU identifier.

Be sure though to check the voltage settings of the BIOS chip when you want to flash it on the machine itself. Mine were, for some reason, set incorrectly (12V instead of 5V) so I'm very glad that I checked beforehand. I got some info about that from this topic: Re: Question about and need bios update for PVI-486SP3 and P/I-P6NP5

Thanks everyone for your help.
I have just got it working - was due to outdated bios version.

I built a tommyPROM eeprom writer https://github.com/TomNisbet/TommyPROM and then used a 28C512 eeprom. It is 32pin vs the original 28pin 27C512 EPROM on the board but the board had a 32 pin socket and the difference between the two chips pinout is basically VCC and the write pin.

Burnt the latest ROM (attached here - P895v14.zip) for anyone who needs it in future.

Doing that and the putting the jumpers in the position showed in the attached document (895JUMP.PDF) and that did it

**JUST REMEMBER TO CHANGE THE BOARD TO 3.3v - IT ISNT MENTIONED IN THAT DOCUMENT!**

Now running happily at 133MHz 😀

HandOfFate wrote on 2020-06-14, 00:03:

Sorry, I forgot to check this topic again. […]
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Sorry, I forgot to check this topic again.

In my case it did still POST at 133MHz but it failed once the OS wanted to start. It did show the table with system specs but my boot disk didn't load, or it showed the "MS-DOS is starting" text and then the cursor started to move diagonally across the screen.

I have no experience with flashing chips with a programmer. I managed to do it on the machine itself by changing the CPU jumpers so the CPU would run in '3x' speed (because '2x' with the 5x86 makes it go '4x' instead), making it run at 100MHz. That allowed me to boot to DOS, so I could backup and flash the BIOS with Uniflash.

After that I could put the CPU back to '4x' mode and it booted fine. The BIOS then also showed the correct CPU identifier.

Be sure though to check the voltage settings of the BIOS chip when you want to flash it on the machine itself. Mine were, for some reason, set incorrectly (12V instead of 5V) so I'm very glad that I checked beforehand. I got some info about that from this topic: Re: Question about and need bios update for PVI-486SP3 and P/I-P6NP5

Isn't the AMD 5x86 133ADZ supposed to run at 3.45Volts ?

I don't think 3.3V is enough to get a POST screen.

Mine would disagree with you 😉
POSTs fine with board on 3.3v

You are right to say the chip is labelled 3.45v but from what I read, most 3.3v boards actually supply a little over.

computerguy08 wrote on 2020-06-14, 22:06:

Isn't the AMD 5x86 133ADZ supposed to run at 3.45Volts ?

I don't think 3.3V is enough to get a POST screen.

Good to hear that it worked!

And thanks for the link to the breadboard EEPROM programmer. I might make one as well 😀

computerguy08 wrote on 2020-06-14, 22:06:

Isn't the AMD 5x86 133ADZ supposed to run at 3.45Volts ?

I don't think 3.3V is enough to get a POST screen.

Mine also works with the motherboard set to 3.3V. My Asus 486SP3 motherboard only has a jumper for changing it to 3.6V for Cyrix CPUs