After working with me about 6 years, my K6-2 450 CPU and mvp3 mainboard has been burnt yestoday, it was really a  
 spirited burn. Many chips has been detroyed. One of them smoked when been burnt.
The awful thing began with auto halt of machine. Maybe it was caused by a defective K6-2 475, it can't work at its frequency a long time ago, but a less frequency of 450. At last, it came at its end yesterday.
For my mistake, this caused the destroy of mainboard, I found the fan didn't work when plus power pin onto mainboard. So, I removed one of two power pins from mainboard. The unfortunate thing happend: a little chip began smoking. Many chips was so burned. No any necessity to fix all of them, the mainboard repairer man told me. And the CPU is dead too.
I got a impress lesson, don't operate anything on computer hardware which you are not sure when the power is on!