Need advice - stuck stabilising Classy 760

[SoulsCollective]

I seem to have run into a wall as far as pushing my Classified / i7 920 combo any further. I can get a stable 4.1GHz using 21x turbo multi and 195 BCLK, using 1.35vCore/~1.45vTT. Passes multiple runs of Linpack (using IBT) with a 4GB working set. However, I've been trying to push BCLK to 200 and above to try for 4.2 and higher as well as run my RAM at DDR3-2000, and I just can't seem to get it to play nicely.

With CPU multi dropped down, I can do 200 BCLK quite happily - 1.3 vCore, +200mv vTT, vDRAM 1.68 for DDR3-2000. RAM passes multiple runs of Memtest, with CPU multi set to below 20x I can pass multiple runs of Linpack with a 4GB working set. Everything seems fine. However, if I try and raise the multi to 20x (leaving Turbo off for the moment, so 20x200 = 4GHz), I just can't seem to get things stable. I've tried raising vCore all the way up to 1.45V (as above, when using a lower BCLK I only needed 1.35V to be stable), but it doesn't make any difference - I get an "uncorrectable hardware error" BSOD within five minutes of firing up Linpack with a large working set, although I can occasionally complete the standard 5-pass 1GB-working-set run.

I know I can run 200BCLK stable at lower CPU multis, so I don't think I need more vTT, and the RAM will pass multiple Memtest runs, so I don't think it's that either, but I can't help but think there's something I'm overlooking - I feel like I'm trying to brute-force it with voltage, but clearly that's not the solution. To make matters even more confusing, I'm capable of running 4.1GHz (195BCLK, 21x Turbo multi) on far lower volts than I'm currently trying to use to get 4.0GHz stable (200 BCLK, 20x multi).

Any suggestions?

Current BIOS settings:
200 BCLK, 20x multi, Turbo disabled, HT enabled, all cores active, BIOS E76051
QPI: 4.8GT/s
vCore: 1.45
vTT: +200mV
CPU PLL vCore: 1.8
IOH PLL: 1.8
QPI PLL: 1.25
vDIMM: 1.68
IOH vCore: 1.125
IOH/ICH I/O: 1.5
vTT PWM Freq: 610
CPU PWM Freq: 1210
CPU Impedance: Less (on recommendation from eVGA forums)
QPI signal compensation: Middle (again on recommendation)
PCI-E clock: 104

WC'd, sig-rig. Temps don't rise above low 70s under load.

[mk-ultra]

try this

Current BIOS settings:
200 BCLK, 20x multi, Turbo disabled, HT enabled, all cores active, BIOS E76051
QPI: 4.8GT/s
vCore: 1.45
vTT: +200mV
CPU PLL vCore: 1.8
IOH PLL: 1.8
QPI PLL: 1.3
vDIMM: 1.68
IOH vCore: 1.3
IOH/ICH I/O: 1.5
vTT PWM Freq: 490
CPU PWM Freq: 640
CPU Impedance: auto
QPI signal compensation: auto
PCI-E clock: 104

if it's stable lower qpi/ioh until unstability occurs

also what is your uncore speed?

[SoulsCollective]

Uncore is 20x = 4,000.

And no dice, didn't seem to make any difference. In fact, running those settings seems to have done something strange to RAM speed - set speed is now multi -1 - eg. if I set 2:10 in BIOS for DDR3-2000 I get 2:8 for DDR3-1600. Problem shows up in Memtest as well as CPU-Z. I've reverted to stock speeds and timings but it's still not fixing mem speed.

Argh.

[=[PULSAR]=]

I think it may be a vtt issue. Which memory kit are you using and what are you current memory settings? Try using a DMM to take your VTT I know my E760 undervolts .07V from what bios says.

To run my Dom GT 7-8-7-20 2000mhz stock its requires 1.57 VTT 1.50 actual.

[SoulsCollective]

Didn't think to raise vTT. With a lower multi 200BCLK is fine with +200mV, so I figured I wouldn't need to raise it just to up CPU multi. RAM is in sig, OCZ 1866 Reapers.

I'll go try that and report back.

[=[PULSAR]=]

Well since the VTT connects memory to cpu lowering the cpu speed would put less stress on that bridge allowing the memory to run higher without increasing VTT.

[SoulsCollective]

GLEAT ZUCCESS.

20x200 is stable with +225mV vTT. Thanks for the tip.

However, RAM is still stuck on lower divider. Any ideas? It was previously Memtest stable at 2000, it's just it seems to be stuck on a divider one lower than whatever I set in BIOS.

[=[PULSAR]=]

No idea, I would reset cmos and start from scratch just remember your important values like vcore and vtt. One thing I hate is screwing around with bios so much you don't even realize how you got it to work in the first place. 200x20 shouldn't be that hard to do with most settings on AUTO.

[cstkl1]

200 BCLK, 20x multi, Turbo disabled, HT enabled, all cores active, BIOS E76051

QPI: 4.8GT/s
vCore: 1.45 ( determine ureself )
vTT: +200mV
CPU PLL vCore: 1.5
IOH PLL: 1.5
QPI PLL: 1.1
vDIMM: 1.68(determine ureself)
IOH vCore: 1.1
IOH/ICH I/O: 1.5
ICH 1.05 : 1.1
vTT PWM Freq: 2xx
CPU PWM Freq: 8xx
CPU Impedance: Auto
QPI signal compensation: Middle ( For ht on , Auto for HT off)
PCI-E clock: 103

tFAW 30
RTL for 2k C8 is 58,61,63
MCH Stap 1600

the latest bios tFAW is too tight for high dram clocks
the RTL channel B and C also is too tight.. usually +1 difference at high dram clocks