You will probably need to try some different CPU jumper settings on the motherboard.

Ones that look like they may work according to the documentation may not work with the AMD 5x86.

Setting it to an Intel setting may help.

Do you have the documentation for the motherboard?

The only documentation I have regarding the jumper settings on the motherboard is this PDF from The Retro Web : https://theretroweb.com/motherboard/manual/pa … 3a528225905.pdf

I feel like the only relevant jumpers would be the RNA/RNB/RNC: CPU Type jumper and the JP11: Clock jumper.

JP11: Clock
2-3 486DX50, 1-2 All others (SX/DX/DX2/Overdrive)

RNA/RNB/RNC: CPU Type
(RN=Resistor network, a single-inline 6pin little item)
RN is placed in one, and only one, of the three sockets.
RNA 486DX, 486DX2
RNB 487SX, Overdrive
RNC 486SX

Currently, JP11 is set on 1-2 for "all others" and the CPU Type is set to RNA, as the PNY Quickchip 133 manual recommands the motherboard jumpers to be set as 486 DX 33 MHz, 5 volts.

Do you think I should set the CPU Type to RNB?

Thanks again!

OK so changing the the CPU Type resistor network on the mobo to RNB and RNC doesn't seem to change anything.

Hi juicylink,

Problems with running an Am5x86-133 CPU on these early 1991/1992 486 boards like your PAT48SA is usually due to an incompatible BIOS.

Looking at https://theretroweb.com/motherboards/s/tmc-my … t48sa#downloads I see two AMI BIOS versions. The 121291 has 486SX and 486DX support, and the latest 111192 version adds 486DX2 support to that.
Experience shows that these 1991 and 1992 core AMI BIOSes can run an iDX4, although they will be indicated as ‘486DX or 487SX’ by the BIOS.

So what I would try first is to run the PNY Quickchip at x3 muliplier mode. On page 19 of the manual are three different dip-switch setting options to try. At least one of these settings will cause the Quickchip to behave exactly like an iDX4.

When this works, you can reach 100MHz CPU speed on a 33MHz bus and you know the CPU is good.

I will keep my fingers crossed, 😉
Jan

Hi Jan!

Thank you for the insightful tip. Unfortunately, I have tried the x3 combinations as well as the extra x3 combinations found here:
https://web.archive.org/web/19990913211357/ht … ddsettings.html and none of them worked. 🙁

Could a BIOS upgrade do the trick? Mine is indeed from 1992 and might be too old for x3 or x4 cpus. Can they be easily upgraded? I found out that there was an universal BIOS called XTIDE floating out there. Could it help with the cpu compatibility?

Thanks again!

Troubleshooting a non-boot issue with a specific CPU calls for a check of that CPU in another 486 board first, so you know the CPU is good. If not, it’s time to get a refund. 😉

Basically a BIOS update could help. However there are no newer BIOS versions for your PAT48SA than the 1992 BIOS you already have, so a later BIOS for a comparable board with the same SiS 85C461 chipset must be found.
Looking at https://theretroweb.com/bios/?chipsetId=415 a number of SiS461 080893 AMI BIOSes are out there but these BIOSes have no dedicated iDX4 support either. So these 1993 BIOSes will probably not help for running the Am5x86.

Before I embark on a wider search for a BIOS upgrade, I like to know if your PNY QuickChip is good. 😉

Then there is the issue of actually upgrading the BIOS. On these 486 boards the BIOS is usually stored in a 64KB UV-EPROM chip like a 27C512 or equivalent that (hopefully) is mounted in a 28-pin DIP socket. 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 advice to use a W27C512 EEPROM. These are compatible with 27C512 UV-EPROMs but can be electrically ereased for re-programming. No hassle with UV-light anymore.

In any case, you need an external programmer to program the BIOS in the (E)EPROM chip. If you don’t have this equipment, maybe someone who has can do this for you.
Note that BIOS Flashchips that can be erased and re-programmed in the motherboard by using a flash tool came several years later (1995).

The XTIDE Universal BIOS is a small add-on ROM for (larger) IDE Harddisk access only and it doesn’t replace the motherboard BIOS.

Cheers, Jan

Thanks again, Jan.

You're right, I better go test the Quickchip on another board. Unfortunately, I don't know anyone in my entourage who has a compatible board. I'll try my luck on my local Vintage computer enthusiast Facebook group.

I just checked for a t48 programmer and they seem to be on the expensive side, so I'll see if I can borrow one or build one of the Arduino chip programmer projects if the Quickchip works on another board.