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[SOLVED] Q9550 @ 3.8GHz failing Prime95 Large FFTs

post #1 of 38
Thread Starter 
Hello!

I'm having trouble with my OC passing Prime95 Large FFTs. Core #3 & #4 error right away when loading Large FFT. I've tried all sorts of voltages for my FSB and NB but none would make me pass Large FFTs. Can anyone help me find the right FSB term & NB v combination?

Here are my settings (Asus P5Q Deluxe):
CPU Ratio Setting: 8.5
FSB Frequency: 450 MHz
FSB Strap to North Bridge: 400 MHz
DRAM Frequency: 900 MHz
DRAM Timings: 5-5-5-18

CPU Voltage: 1.300v
CPU GTL Voltage Reference (0/2): AUTO
CPU GTL Voltage Reference (0/2): AUTO
CPU PLL Voltage: 1.50v
FSB Termination Voltage: 1.20v
DRAM Voltage: AUTO
NB Voltage: 1.30v
NB GTL Reference: 0.670

Load-Line Calibration: Disabled

I've no problem with vcore and temps. I've already passed small ffts but constantly fail the large ones. I've tested my rams and they're okay.

I've found that upping the FSB Termination doesn't help and causes instability. Upping NB voltage to 1.40v produces blank screens (can't boot - no output from monitor).

I'm going out of my mind!!! Help!!!
-UPDATE-
Now running at 4GHz (471x8.5) drum.gif

Here are my stable settings:
CPU Ratio Setting: 8.5
FSB Frequency: 471 MHz
FSB Strap to North Bridge: 400 MHz
DRAM Frequency: 943 MHz
DRAM Timings: Auto (default 5-5-5-18-52)

CPU Voltage: 1.275v
CPU GTL Voltage Reference (0/2): AUTO
CPU GTL Voltage Reference (0/2): AUTO
CPU PLL Voltage: 1.56v
FSB Termination Voltage: 1.26v
DRAM Voltage: AUTO
NB Voltage: 1.32v
NB GTL Reference: Auto

Load-Line Calibration: Enabled

Lesson learned:
Just because Prime95 large fft focuses on FSB term and NB (and RAM) that doesn't mean vcore is completely excluded from testing

Overclocking advise:
1. Follow KingT's advise of first running Prime95 large fft for 6 hours using 471 x 6 to determine the appropriate FSB term and NB voltage required. You're running x6 multiplier so you don't have to worry about vcore.
2. If you're stable for 6 hours, that's a good start. It means your FSB term and NB voltages are ok. If not stable for 6 hours, tweak FSB term and/or NB voltage (usually NB voltage)
3. Now up the multiplier to x8.5 and run at 1.3v (vcore) - this is usually a good starting point
4. I found that setting RAMs to their default timings helps stabilize the OC, so I left them at default. If you want to tweak your timings, do it after you stabilize your OC.
5. Run IBT high or max for 20 runs. See if it's stable. You should be getting around 52-54 GFlops @ 4GHz
6. If it's stable, run large fft for 4-6 hours. If it's stable then I'd call it stable smile.gif
7. If it's stable, your next goal is minimizing your vcore. Go back to bios and drop vcore by 1-2 notches and repeat #5 & 6 (I know, it's tedious frown.gif)

That's all! I found that for my Q9550, large fft is a better test of stability than small fft. This is because I can run small fft for the longest time but still fail large fft within the first 30mins (1 worker would fail). It turned out my vcore was set too low (1.25v) and no matter how high I upped the FSB term (up to 1.34v) and NB term (up to 1.42v), large fft would still fail. So that's where I got the lesson learned part. haha!
Edited by pipnasty - 1/12/11 at 8:05pm
post #2 of 38
Im not familiar with the 'Q' series, is that the max multiplier? If no put on the max multi, and second of all try upping the Vcore to 1.375
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post #3 of 38
Take your D-Ram voltage off of auto, thats most likely your culprit right there. Default voltage for your ram should be 2.1v-2.2v .

you may need more Vcore too, depending on your chip, takes 1.36v in bios for me to get that clock.
post #4 of 38
Thread Starter 
I'll try upping the Dram voltage. Vcore isn't the issue since the OC's failing large ffts (indicating FSB term/NB/Ram). My vcore is actually stable at 1.21875v (LLC enabled) and passes 4hrs of small fft, but constantly fails at large fft.
post #5 of 38
Yeah you going to need, a little more vcore i need it 1.38v for 3.8ghz and my vid is 1.2875v whats your vid?
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I7 Antec 900
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post #6 of 38
Quote:
Originally Posted by pipnasty;11872542 
I'll try upping the Dram voltage. Vcore isn't the issue since the OC's failing large ffts (indicating FSB term/NB/Ram). My vcore is actually stable at 1.21875v (LLC enabled) and passes 4hrs of small fft, but constantly fails at large fft.

Ive had small fft's fail 5 hours in, you may want to run it a bit longer, or run blend for a long time. IBT doesnt hurt either biggrin.gif

You however are correct about large fft's being related to MCH, and Ram related. Im certain that your board was undervolting your ram, board default is usually around 1.8v, and at those speeds you would need at least 2.1v.
post #7 of 38
Getting a Core 2 Quad to be LARGE FFT stable in Prime 95 is much harder than it seems. You can't just leave settings on AUTO.

It requires some patience, skill, and a bit of luck.

Try to increase VTT to 1.26v and DON'T leave CPU GTL_Ref on AUTO.

They are one of the most important settings for achieving stability at higher clocks.

Your motherboard has what it takes to stabilize that CPU to 4ghz no problem, you just need to play with VTT and GTL_Refs and change some of your settings.

To begin with try the following:

Try setting both CPU GTL_Refs @ the .63x multiplier and see how it goes.

Set FSB STRAP to AUTO (P5Q series has problems with FSB straps)

Set your DRAM voltage to at least 2.0v.

Set CPU PLL to 1.54v

Enable Load Line Calibration with your current Vcore (1.3v)
Edited by PanicProne - 1/3/11 at 5:12am
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post #8 of 38
Thread Starter 
Quote:
Originally Posted by Abrajam;11872545 
Yeah you going to need, a little more vcore i need it 1.38v for 3.8ghz and my vid is 1.2875v whats your vid?

Mine's an E0 with a vid of 1.200v. The previous owner claimed it could go 4GHz @ 1.2v!!! Too bad for me I can't frown.gif
Quote:
Originally Posted by Mattb2e;11872573 
Ive had small fft's fail 5 hours in, you may want to run it a bit longer, or run blend for a long time. IBT doesnt hurt either biggrin.gif

You however are correct about large fft's being related to MCH, and Ram related. Im certain that your board was undervolting your ram, board default is usually around 1.8v, and at those speeds you would need at least 2.1v.

Yeah, I run IBT max for 20-25x. I find Prime takes too long :S I've currently upped the DRAM voltage. Still fails but I'm leaving it at 2.0v (5-5-5-18-50 @ 900Mhz).
Quote:
Originally Posted by PanicProne;11872578 
Getting a Core 2 Quad to be LARGE FFT stable in Prime 95 is much harder than it seems. You can't just leave settings on AUTO.

It requires some patience, skill, and a bit of luck.

Try to increase VTT to 1.26v and DON'T leave CPU GTL_Ref on AUTO.

They are one of the most important settings for achieving stability at higher clocks.

Your motherboard has what it takes to stabilize that CPU to 4ghz no problem, you just need to play with VTT and GTL_Refs and change some of your settings.

To begin with try the following:

Try setting both CPU GTL_Refs @ the .63x multiplier and see how it goes.

Set FSB STRAP to AUTO (P5Q series has problems with FSB straps)

Set your DRAM voltage to at least 2.0v.

Set CPU PLL to 1.54v

Enable Load Line Calibration with your current Vcore (1.3v)

Really? Someone told me to leave those CPU GTL refs on AUTO since I'm not going too high on the vcore. I'll try setting the strap to AUTO, CPU PLL @ 1.54v (what does this do anyway?). I'd like to leave LLC disabled bec. I read in some forums that it causes memory slot failure overtime. I don't know if it's true but better safe than sorry.

Thanks for the replies!
post #9 of 38
Quote:
Originally Posted by pipnasty;11872644 
Mine's an E0 with a vid of 1.200v. The previous owner claimed it could go 4GHz @ 1.2v!!! Too bad for me I can't frown.gif



Yeah, I run IBT max for 20-25x. I find Prime takes too long :S I've currently upped the DRAM voltage. Still fails but I'm leaving it at 2.0v (5-5-5-18-50 @ 900Mhz).



Really? Someone told me to leave those CPU GTL refs on AUTO since I'm not going too high on the vcore. I'll try setting the strap to AUTO, CPU PLL @ 1.54v (what does this do anyway?). I'd like to leave LLC disabled bec. I read in some forums that it causes memory slot failure overtime. I don't know if it's true but better safe than sorry.

Thanks for the replies!

The person who told you that is wrong.

CPU GTL Ref tuning is essential to stability with high clocks when overclocking Core 2 Quads CPUs.

CPU PLL is actually important in achieving and stabilizing higher FSBs (you will want to stay below 1.6v for safety reasons).

LLC Is perfectly safe to have enabled if you are using low Vcore and a high quality board. Which is your case.

It won't kill RAM slots lol, don't worry about it. Where do you get this misinformation?

You have one of the best P45 motherboards in existence, it can take all sorts of abuse.

Trust me, I've had a P5Q board before and a Q9550.
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post #10 of 38
Quote:
Originally Posted by pipnasty;11872644 
Mine's an E0 with a vid of 1.200v. The previous owner claimed it could go 4GHz @ 1.2v!!! Too bad for me I can't frown.gif



Yeah, I run IBT max for 20-25x. I find Prime takes too long :S I've currently upped the DRAM voltage. Still fails but I'm leaving it at 2.0v (5-5-5-18-50 @ 900Mhz).



Really? Someone told me to leave those CPU GTL refs on AUTO since I'm not going too high on the vcore. I'll try setting the strap to AUTO, CPU PLL @ 1.54v (what does this do anyway?). I'd like to leave LLC disabled bec. I read in some forums that it causes memory slot failure overtime. I don't know if it's true but better safe than sorry.

Thanks for the replies!

Your specified ram settings from the manufacturer are 2.0v-2.1v @ 5-5-5-12
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