Learn something new everyday, didn't know this myself and the p5a series is my favorite....thought only the ''+'' were affected. Found this on the web somewhere, if your test with a slower/older cpu works please confirm. Perhaps the mod i linked to earlier will also fix this problem?
it depends on the chip to some extent the first few batchs of 500, 533 and 550 chips will run fine on the any P5A but the newer batch's sence around the time the + line of chips came out do not. I know some people running these combos and there fine I also now some people who tryed these combo's and they did not work ?
Any way this is what I do Know
AMD made a change to the core instruction set to all newer K6 chips that makes them incompatible with the ICC chip on the revision 1.5 and 1.6 P5A and P5A-B motherboards and the 1011_4 beta will show the correct speed and chip and even identifiy the + chips correctly but the problem is not with the bios it's with the Hardware on the board as in the ICC chip
if your getting really low benchmark results as in your system is benching like a P200 then you have this problem and no bios or tweak program is going to fix it I tryed them all on 3 diffurent Asus P5A's rev. 1.6 motherboards with 2 diffurent K6-2-500's and a K6-3+ 450
pop the same chips in a POS Amptron all in wonder, a FIC 503+, and a Acorp Ali5 and they run fine and bench normal put then in a P5A boots fine acts'like it's running fine just kinda slow bench them and it says there running like P100's ?
you can try the beta bios and all the tweak prog's out there but I'd bet it's not going to help.
asus tx97-e, 233mmx, voodoo1, s3 virge ,sb16
asus p5a, k6-3+ @ 550mhz, voodoo2 12mb sli, gf2 gts, awe32
asus p3b-f, p3-700, voodoo3 3500TV agp, awe64
asus tusl2-c, p3-S 1,4ghz, voodoo5 5500, live!
asus a7n8x DL, barton cpu, 6800ultra, Voodoo3 pci, audigy1