Why does 11x200 work, 5x220 work, but not 10x220

Ok look at my signature for my pc specs. Here's the deal, I have an athlon Xp thouroughbred B, that handles 203x11 fine. My ram can't handle higher than 203 but I'm planning to replace it soon. To test how high my fsb my motherboard can handle I turned ram down do 50% and was able to run stable at an fsb around 220mhz. The thing was I turned the clock multiplier for cpu way down so 5x220, but when I set the clock multiplier to 10x220 the cpu either won't post or is unstable. Now why is that? My cpu can handle fine 2.2Ghz running prime95 for hours when fsb is 203mhz. Why can't my cpu handle 2.2Ghz when fsb is 220. Any ideas? Before I buy new ram I need to know what my fsb speed my motherbaord can handle so I can purchase the right speed. I'm bassically after running at higher fsb rates that my cpu and ram can handle. Thanks

Make sure you set your memory Frequency to 100%, not Auto or any other value.

Now increase the Vdimm RAM voltage all the way, lower the multiplier and start increasing the FSB...

If you have Vdd North bridge voltage adjustment option, (not all boards do) see if messing with that helps you after you hit the wall with low multiplier and high FSB.


Be sure to put that Memory Frequency to 100% not 50%....

Well, at the moment I can't because my ram can't handle past 203mhz 11,3,2,2.0 . The reason I'm doing this now is because I don't want to end up purchasing 230mhz fsb capable ram or whatever and then learning that my cpu can't handle running at around 2.2ghz that it is at right now. My vdimm right now is set to 2.9, which is the max the motherboard will do without a mod. I tried vdd at 1.8, but haven't tried the 2.0v option, will 2.0 fry my northbridge? I did replace the stock heatsink with a iceburg fan.

Well first off, relax your RAM timings, set those to Automatioc not tight like 11,3,2,2.0.

Now lower the multiplier and try to see if you can hit pass 203 FSB.

Ok, I'll give it shot, I've been able to post with the ram at higher fsb than 203mhz, I've gotten as high as 215 but the ram has been unstable, making it difficult for me to test whether the cpu and northbridge are stable at that speed.

Well, even when setting timings to the lowest, the ram fails memtest on the 5th test which is the one that always first tells me whether the ram is clocked to high or not. I wasn't able to clock 10x220 period, although 9.5x220 or even 9.5 by 230 worked although besides the ram failing the fifth test in memtest when I started windows I got the blue failure screen leading me to bet that 230mhz is above what my fsb can handle although I can't know for sure as the ram might be the cause of all the problems. Anyways if it is indeed the case that I can't get 10x220 when I get new and better ram would I still be better off with a system that ran at 220fsb and 2.1ghz or a system of 203fsb and 2.25 ghz?

I would do a search for your motherboard model and see if anybody out there has it running at higher FSBs with RAM sticks that can take it...

Do you have extra cooling on the northbridge and mofsets? I have a small fan strapped to my stock northbridge heatsink and I put some chipset sinks on the mofsets and it runs very stable at 220fsb.

The stock northbridge heatsink with this board often has a lousy contact with the chipset, so you may also want to remove it, clean it, and put some arctic silver on it. Most people just replace it with a vga cooler. Good luck!

yeah, I have an iceburg fan on the northbridge, the southbridge has the original heatsink.
For some reason I think my board can handle 225mhz fsb or so, but for some reason like the title of my thread suggests my cpu gets unstable or simply doesn't work when 10x220.

I have a simular problem, my mobo won't post with a 13x166 no matter what, eventhough I'm able to run the cpu at 2.160mhz stable with a different combination.