First post, by Durandal
I was given a Cyrix 5x86-133 and decided to test it today. The only 486 board I currently own is from a Japanese IBM motherboard that is only really identified by the part number 66G3602, I believe it's out of an IBM PS/V Type 2410 PC. It came with a 486DX2 66MHz and has been working perfectly since I got it, running IBM PC DOS J6.3/V from a 2GB compact flash card (450mb~ C: partition I think) with no issues.
I made sure the 5x86's pins were all straight, inserted it into the CPU socket, connected the cooling fan and powered it up... only to be greeted by a "DIVIDE OVERFLOW" error message when booting from that same J6.3/V CF card. Googling didn't really help, a lot of vague things about software issues or straight-up hardware incompatibility.
Then I tried booting from a Win98 DOS boot floppy, which let's me select which version to load (with or without CD-ROM support) but both options just hang after the floppy seeks a few times. The cursor flashes indefinitely and I have to either turn off the PSU or reboot with CTRL-ALT-DEL. I also tried a DOS 6.22 boot floppy and it got to "Starting MS-DOS..." then it halted completely with a flashing cursor, CTRL-ALT-DEL didn't even work.
So what's going on here? Is the board simply incompatible? Due to it being made by IBM Japan I can't find any information about the board online which means no known jumper settings. There are jumpers spread across the board however they aren't labeled by anything except numbers (J1, J2, etc.). And I'm not sure it's relevant, but in the middle of the CPU socket it has "80486DX2 OD" silkscreened on the PCB, thought I'd mention it anyway.
The only information I found regarding putting CPU upgrades in this specific board was this:
My hunch was that the board was feeding the CPU 5V instead of 3.5V, but near the bottom of that page they mention using an AMD-x5-133ADY "P75" CPU in this motherboard which is a 3.45V CPU, so it must be able to lower itself automatically assuming that person doesn't have some sort of jumper chart.
Any suggestions? 😕 😕 😕