P5B & C2D FSB vs PCI-e Bus Issues

Hi Guys,

I know several other people have posted similar threads to this one, but none of the suggestions seem to resolve my problem.

PROBLEM:
Overclocking the FSB on my P5B above 360 will automatically drop the PCI-e bus width from 16x to 1x

SUGGESTED/ATTEMPTED SOLUTIONS:

- Increase PCI-e frequency gradually until 16x Bus width is restored (gone from 100 - 120 without any effect)

- Reduce multiplier to either 8x or 7x but increase FSB above 400 because apparently some instability can occur on P5B's with the FSB range 360-400.
(Have tried 8x ...lots, and can't seem to post, tried 7x 401, 405, 410, 420 and lastly 425 (425 would not post, but the others will post and not fix the problem)) I have tried this in combination with adjusting PCI-e frequency up to 120 and it doesn't resolve the issue.

- Increase South Bridge voltage to 1.7 and see if this resolves the issue - doesn't seem to

- Set overclock and close down without posting, leave power out for 30 seconds and reboot. - no difference

- I've heard some suggestions as extreme as setting the overclock, removing gfx card?!?! powering on, and then off. Then re-inserting gfx card .... not tried this one, and not really likely too to be honest.

Has anyone got any further suggestions I could try? or even suggestions as to the cause of such an issue? I've thought to myself it could be the PSU underpowered, and maybe the power put through the PCI-e bus is not high enough to hold 16x and it therefore reverts to 1x.
Many people seem to disagree with this as a cause, but I'm running low on other causes.

A work colleague suggested that I try a different gfx card and see if this helps (could be a factor in the power consumption) but I don't have another PCI-e card I can use to test I'm afraid.

Any help would be hugely appreciated, as I know the CPU/Mobo/RAM can handle 360+ on 9x multiplier as I can run higher with no problems, but I'm obviously not prepared to drop to 1x PCI-e to acheive this.

Ok, edited this.

Strange thing, set the PCI-e frequency to 115 on FSB 360, and booted, restarted and set fsb to 361 and rebooted.....YES!!! kept the 16x FSB!!!

Rebooted to try and reset PCI-e frequency to 100, but got a nasty bios beep.

Using this methodolody, I reset PCI-e frequency to 100 and fsb to 360 and tried again.

This time i set PCI-e to 105 and booted, restarted and then set fsb to 370!! Loving this, booted in 16x!!

This raised a few questions:

1. I started to wonder, what would the correlation be between PCI-e frequency and FSB?

2. Could i just push PCI-e to 101 and reach 400 fsb?

3. Would i need to increase the PCi-e frequency to acheive higher FSB's? or would #2 be true?

4. What SHOULD i keep the PCI-e frequency at? would there be any harm in keeping is at 105 and running 360+ FSBs?

Clunk has suggested once i hit say 370x9 using 105 PCI-e frequency, that I should be able to reduce back to 100 and still keep 16x PCI-e bus. This hasn't seemed to be the case in my example, but just going to try some combinations and see what happens, will post update ASAP.

If what I suggested in this thread doesnt work, then, I would do the full cmos clear with battery out, ram out, graphics card out, psu unplugged, and see what happens.

Also, have you tried disabling legacy usb? I know you have a usb keyboard, but it might be worth testing with a ps2 keyboard to see if that affects things.

Also, try the same overclock with just one stick of RAM, and see if that does anything.

Try giving the NB its max voltage and try the 115 pci-e trick, then check in cpuz, restart, and set back to somewhere around 100-110.

Without commenting on your last post Clunk (which i will do in due time (asn i really do appreciate the advice and help)) here is a list of PCI-e frequencies and FSB's I've tried.

Start point:
#1 pci 100 fsb 360 = pci-e 16x

#2 pci 105 fsb 360 = pci-e 16x (to be expected really)

#3 pci 105 fsb 370 = pci-e 16x

#4 pci back to 100 fsb 370 = pci-e 1x

#5 pci 105 fsb 380 (didnt' have to reset to start point at this point, 105 - 370 seems happy) = 16 pci-e

#6 pci 105 fsb 390 = pci-e 1x (doh)

#7 reset to pci 105 fsb 380 = pci-e 16x

#8 pci up to 110 fsb 380 = pci-e 16x

#9 pci 110 fsb 390 = no post

#10 reset to pci 110 fsb 380 (last successful post) = pci-e 16x

#11 pci 110 fsb 385 = pci-e 16x

#12 reverted to pci 105 fsb 380 for the time being.

Seems I can happily reach 380 fsb using pci frequency 105, and upping to 110 pci frequency I can reach 385.
I am having trouble hitting 390 with 105 or 110 pci-e whilst still keeping 16x pci express link width.

...now reading your previous post Clunk, it would certainlty be worth me looking at the legacy usb stuff.

I will test with only one ram when i get a chance.

I am concerned about the need to revert to 100 pci frequency though. Some people have said overclocking the PCI-e bus shouldn't really cause any issue, but others say they do.
Would you think 105 and 380 fsb would be ok, or should i drop back to 100 and 360 until i can find a way to get the fsb up without keeping the pci frequency higher?

You dont have to revert to 100, but for most people, that works fine. As it doesnt work for you, I would think that your problem might be a bit more permanent (RMA it), or caused by something else entirely.

I ran my P5B at 110 pcie for months, with no problems, but in later bioses, auto worked fine.

I do suspect that you have some other problem though.