Sounds like heat damage to the CPU. You may be able to tweak a higher stable speed by lowering the bus speed and raising the multiplier. Current thinking though is that higher bus speeds are better than higher total clock speeds.
Take the chip back to the supplier, ask for a replacement - if he quibbles (cf Dixons managers) point out that no thermal paste/contact was supplied. Just to make your day I'll add that my K6II-500 clocks to 550 (actually 551.24) happily. To be honest my Voodoo3 graphics chip is more of a heat problem.
On the topic of memory testing, software based testers can't always detect faults. The only really reliable way to do it is with a memory test scope (can a general oscilloscope be used?) . Hewlett Packard do some particularly fine ones.
#From: ilug-admin at linux.ie [mailto:ilug-admin at linux.ie]On Behalf Of
#Following Padraig's advice, I ran memtest86. I let it run for 17
#hours (got to
#test 6) with no errors occurring. When I reset the speed, I set the CPU bus
#clock to 100Mhz, then I just turned down the CPU multiplier to 4x.
#I'm more starting to feel like an idiot to have bought the thing. I never
#guessed to was going to be so much of a problem temp. wish.
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