This is my setup:
mobo: abit nf7-m v1.21
cpu: athlon xp-m 2500+
ram: 2x512mb ddr400 corsair valueselect

I cannot seem to get a stable overclock on this thing anywhere past about 170mhz fsb, anything higher and prime95 detects errors anywhere from after 15 minutes to after 5 hours of torture testing. I've upped the cpu voltage to 1.575V, DDR voltage to 2.8V and still unstable. I havent tried upping the chipset voltage yet. Just out of curiousity, what is the upper voltage limit on these mobiles since I still have room temperature-wise (44C full load).

Interesting thing is, my old athlon xp 2800+ (non mobile), ran fine at up to 180mhz fsb, so I'm wondering which of my parts may be to blame here for the poor overclock.

Any ideas appreciated, thanks.

I had my old AMD xp2800+ running 200MHZ FSB without added voltage. 2.2GHZ. I lowered the multiplier by 1.0 and raised the FSB instead. Try that if you haven't already.

Hard to tell what you are doing wrong not knowing exactly what you tried. Did you loosen your timings? Tried locking down PCI? so on...

i'm running the timings at 2.5-3-3-8 as is the SPD on the corsair ram at 200mhz (from cpu-z).
i'm not exactly sure what you mean by "locking down PCI", is it the "Enhance PCI performance" option in the BIOS?

i'm currently trying the settings as per the screenshots here:
http://www.pcstats.com/articleview.cfm?articleid=1362&page=3
with the following exceptions:
RAM timings: 2.5-3-3-8
Enhance PCI performance: disabled
Multiplier factor: 14.0
cpu voltage: 1.6v
ddr voltage: 2.7v
chipset voltage: 1.6v
agp voltage: 1.5v

the only 200mhz FSB setting i've tried was 200x11.0=2200mhz, a very conservative oc in my opinion, running at about 40C after 5 or so minutes of prime95, at which point i got an error.

i cant seem to understand what exactly in my setup cant handle the 200mhz fsb.

if it isnt too much trouble, could you let me know what settings you would use for a 200mhz fsb oc, perhaps i have overlooked something trivial...
thanks.

I don't know if your mobo can even lock down the PCI, not many of the old socket 462 mobo can, look in your manual. The thing is, when you OC the FSB you OC the PCI and AGP bus as well if you haven't locked it (a-sync) or what ever it's called... may be what what is holding you back... but I'm not really sure since it does at least POST.

I haven't OC'ed a mobile CPU my self, but for my 2800+ barton all I did was lower the FSB from 12.5 to 11.5 and then I cranked up the FSB from 166 to 200, I didn't lock the PCI bus or anything. I did lock the RAM though since they where already running 200MHZ and I was going for a 1:1 ratio. (I was using a AsRock K7NF2-Raid mobo)

Can we get an experts opinion plz? ;P

Edit: Read this from geek.com especially the section about "Bus Speed and the ISA / PCI bus" and "Bus Speed and Memory". Hope it helps.

The last settings I mentioned once again proved to be unstable after about 2 hours of stress testing.

I am back to trying a 166x12.5 setup for a resulting frequency of 2075mhz, however I am trying the FSB:RAM ratio "by SPD", so it is currently at 5:6 for a 200mhz memory speed. We'll see what that yields, though I'm sure it will be stable, as I only seem to experience problems when I venture into the 175+ mhz FSB or the 2250+ mhz final CPU speed.

I understand that the PCI bus is also overclocked, which is why I am trying to keep my FSB a multiple of 33, unfortunately there is no divider option in the BIOS for the PCI bus, so I can only assume it uses 166/5=33mhz. Is there a way to check what speed the PCI bus is running at?

My next attempt, I will try lowering the multiplier all the way to 10.5 and cranking the FSB to 200mhz for a 1:1 FSB:RAM ratio and only a 2100mhz final CPU speed.

Thanks for the help so far, more opinions are welcome though.

ok, so currently i have been running Orthos for 1hr 10min with 200x11.0 oc, so far so good, perhaps, setting the fsb:ram ratio to SPD did the trick.