I bought a couple of AMD-X5-133ADZ CPUs from ebay. Unfortunately, one appears to be dead. The other one seems to work. I tried it at 33 FSB, and then at 40 FSB. No problems. I then tried setting the FSB to the next highest setting on the Asus 486 board, which is the undocumented 48 FSB setting. Understandably, I see no BIOS POST on the screen, and so I tried:
* BIOS options set to "fail safe".
* Mobo's wait state jumpers set to 1 Wait and > 33 MHz. BTW, I'm using a PCI video card.
* Mobo's CPU jumper set to write thru cache (not WB).
One thing I could try next is to set the mobo's CPU voltage jumper to 3.6V, which is the Cyrix CPU option. Will this kill the 3.45V AMD CPU, or give it the necessary extra juice in order to run it at this crazy 48 FSB setting? Damn nuisance about the other CPU. It must be dead, because both CPUs are identical, and one works while the other doesn't. Both CPUs had badly bent pins on arrival. 😒
Edit: For the 48 MHz FSB test, I tried removing the PCI video card, and replacing it with a VLB card. No POST. The VLB card works OK, because if I drop the mobo's FSB back down to 40 MHz, the BIOS POST reports that the 133 MHz chip is running at 160 MHz (4x multi * 40 = 160).