Quote Originally Posted by MrBean View Post
@ jcool: As i have mentioned, the cpu's will run at 375x8=3.0gig all day long.

Dropping the multi to 7x at 400fsb gives me only 2.80gig, so theoretically speaking, the cpu's will be ok here. Bluescreens is memory-related, so I will measure vdimm and see if the board is undervolting on the mem.

I will adjust dual-channel voltage setting in the bios and see if I can get past the issue.

Just as an added note, even if I drop the multi to 6x at 400fsb, which equates to 2.4gig on the cpu's, it still bluescreens. So definately memory.

Let me perform a few tests, and I will report back.
No, you didn't get what I was saying. There is a slight possibility that your CPUs simply cannot handle a FSB frequency of 400Mhz, simple as that. Or at least not without VTT/GTL adjustments, both of which are (currently) impossible on the Z7S with non-QX CPUs.

Imagine you are overclocking your Desktop S775 rig. You go to FSB 400 with your Quadcore, but no matter how much you raise MCH, Vdimm or Vcore, you can't get prime blend to run stable. What you do is increase the VTT from a stock 1,1V (for 45nm S775 CPUs) to, lets say, 1,18V and voila, FSB 400 stable. Most CPUs require VTT adjustments only later on (starting at FSB 420-440), but there are some that won't run FSB 400 on stock VTT. I have had at 3 Q9550 in the last 2 months alone that wouldn't do it without adjusting VTT.

Now the Z7S slightly undervolts VTT, if you check in bios you'll see the VTT listed as 1,07-1,08V. What happens for me is that the E5420's can't run over FSB 430 stable, regardless of the multiplier and Vcore used. Even though I know the board, memory etc can go a lot higher singe I am running FSB 450 24/7 with the X5450's

I am not sure what limits my OC with the X5450's, I know for a fact it's neither the memory nor CPU clock (because lowering the multiplier doesn't help getting above FSB 450 primestable), so it's either the VTT again or a simple motherboard limitation.

Anyway, what I am saying is that you just might be so unlucky as to get a pair of CPUs that simply cannot handle FSB400 and upwards with stock VTT.
Again, this is unlikely but possible, and WILL happen with C0 step CPUs between 420 and 440Mhz FSB anyway. You will never hit FSB 450 primestable unless you got E0 step CPUs.