At 11:09 AM 04/01/2001 Catherine Williamson wrote:
>A friend asked me to fix her Cyrix computer which continued
>to overheat . . . .
>So I reduced the speed from pr166+ to pr90+ and also lowered
>the voltage from 3.3 to 2.8 coz I couldn't think of what else to do.
>It now runs beautifully even with the case closed but I keep worrying
>that by doing this I may damage the processor or worse. . . .


Catherine

You didn't say what CPU clock multiplier and Bus speed you used in this
case. Let's go over the basics, for the benefit of those unfamiliar with
Cyrix CPUs.

The Cyrix PR+ numbers are not the actual processor speed settings but are
the Cyrix CPU's comparative rating viz. an Intel CPU.  Cyrix CPUs can
execute 80x86 instructions in multiple pipelines in out-of-order sequence,
making them faster than Intel Pentium Classics at the same clock speed.
However, the actual multiplier and/or bus speed settings required for
similar performance were lower.

Accordingly, a Cyrix PR166+ normally runs at 133MHz (not 166MHz), using a
clock multiplier value of 2.0 and a bus speed of 66MHz. Setting the
motherboard for less than these values should not cause any damage. Keeping
the bus running at 66MHz, and just reducing the multiplier, would reduce
the performance hit.

Regarding voltage, you didn't mention which version of the PR166+ your
friend had, and I assume you checked the voltage rating on the chip itself.
Some versions ran 3.52/3.52 (Core voltage / I-O voltage), others ran
3.3/3.52 and still others ran 2.8/3.52 and 2.9/3.52....

Paradoxically, when you overclock, you must increase the voltage to enhance
signal clarity. Presumably, then, the opposite should hold true, provided
that the signal level is sufficient.

Congratulations on discerning a workable solution. Herbert Graf's
suggestion to use thermal grease is a fine idea (and also try using a
bigger heat-sink/fan). Then you might attempt clocking the CPU back up again.

Regards,

John Chin

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