VIA's KT133A - Overclocking w/ the 133MHz FSB: The "Issue"

Suggestions and Limitations

So now with the last piece of the puzzle revealed, what’s left is is to figure out what you should do with your specific chip.  Keep in mind there are a lot of possibilities, but these are our suggestions for the easiest changes.

Duron 600 and Duron 650

It is actually advisable to try testing the chip directly with 133MHz FSB without modifying the L6 Bridge.  Most Duron 600’s and 650’s can hit 800MHz (6 x 133MHz) and 866MHz (6.5 x 133), respectively.  If you really have to lower the multiplier, you can add one bridge to Duron 600 or two bridges to Duron 650 to lower the multiplier to 5.

Duron 700 and Thunderbird 700

If you have this chip, it will take quite a bit of work, because it is one of those scenarios where you simply have to cut a bridge.  Closing the remaining bridge doesn’t help since you will actually bump the multiplier to 11.  What we suggest is to cut the bridge associated with multiplier adder of 2 and add in the bridge for adder 4.  This will bring the clock multiplier back to 5, allowing the CPU to boot at 667MHz (5 x 133MHz)

Duron 750 and Thunderbird 750

Start by connecting the bridge corresponding to a multiplier adder of 1/2 and see if the chip boots up at 933 (7 x 133MHz).  Most of these CPU’s will be able to obtain such a speed if the voltage is boosted to 1.85V (as mentioned previously).  If you’re not so fortunate, consider using the procedure for 700MHz chips from above to bring the multiplier down to 5.5.

Duron 800 and Thunderbird 800

These are similar to 750MHz chips, so try to connect the bridge corresponding to the multiplier adder 1 and see if the chip boots at 933 (7 x 133MHz). Most of these CPU’s will be able to obtain such a speed if the voltage is boosted to 1.85V (as mentioned previously).  If it doesn’t work follow the instructions for a 700MHz chip to lower the multiplier to 6.

Thunderbird 850

Connect the bridge corresponding to multiplier adders 1/2 and 1, which will bring the multiplier down to 7. This should allow you to boot at 933MHz (7 x 133MHz), which should work in most cases if the voltage has also been boosted to 1.85V (see above).

Thunderbird 900 / 950 / 1000

The L6 bridges of these chips is actually quite similar to those for 500 / 550 / 600 CPU’s.  All you need to do is close the bridge corresponding to adder 4, and that will bring down the clock multiplier from 9 / 9.5 / 10 to 5 / 5.5 / 6, respectively, which is way lower than what you need just to boot.

Thunderbird 1.1GHz

As we mentioned previously, all bridges are closed for a multiplier of 11, so you can’t do anything with this chip unless you cut one of the bridges.  If you do choose to cut a bridge, you can cut either the bridge that correspond to adder 2 or the one to adder 4.  The first case will bring the multiplier down to 5, and the second case will lower it to 7.  Both cases, when booting at 133MHz, will result in clock speed lower than 1.1GHz.

Thunderbird 1.2GHz

Try to connect the remaining bridge to lower the multiplier to 11 and boost the voltage to 1.85V by closing all L7 bridges..  There is a chance that this will not work because you are still trying to boot the chip at 1463MHz (11 x 133MHz), which is more than 200MHz above the 1.2GHz spec, although it may be possible long enough to let the BIOS override to a lower value.  If it doesn’t work, follow the instructions for the 1.1GHz, and you should be able to get the multiplier ratio down to 6 or 8.

The above suggestions are just for references.  We tried to minimize the number of bridges that had to be modified, especiallythe cutting of bridges.  Notice that even in the worst case you will only need to cut one bridge to enable a lower multiplier.  If you figure out a configuration that requires cutting two bridges or more, you should re-consider. Of course, this is just a starting point - we just want the system to boot so we can then go in and modify the multiplier in the BIOS. As always, if you don’t have your motherboard already, we recommend the much easier route of just purchasing a motherboard that is fully jumpered or fully jumperless to avoid the whole issue.