[dEaFTOLiGhT]

First post!

I'm new to overclocking (never tried it until the other night). Read through the clunk's, graysky, and wolfram beginner's guides and got a good idea of it. I was overclocking fine when it came to booting and temps, until I realized the system wasnt stable cause there would be jitters... mainly there would be huge FPS drops in 3dmark.

Anyway, I am doing it on my 4-year-old build:
E6750
4x1GB G.SKILL DDR2-800 RAM F2-6400CL5D-2GBNQ (1.8-2.0V, 5-5-5-15)
Asus P5K-E WiFi AP mobo
EVGA GeForce 9800 GX2
COOLER MASTER Real Power Pro RS-750-ACAA-A1 750W Power Supply

Now this sounds like an entire noob question with a simple answer, but I have spent the last 2 hours googling and couldn't find one. I set my BIOS according to clunk's guide (http://www.clunk.org.uk/forums/overc...s-p5k-add.html). I set my ram timings manually to 5-5-5-15 and ram voltage to 1.8. I set my FSBRAM to a 1:1 ratio, for mine that is 333:667.

Here is the problem: When I overclock my FSB up to to 399 MHz, (DRAM 799 Mhz), I can benchmark in 3DMark and the FPS remains high and the final score raises. But as soon as I bring the FSB up one more interval to 400 MHz (DRAM 801 MHz), the FPS drops severely in 3Dmark, and the final score is about cut in half. The CPU score raises, but the SM2.0 and SM3.0 scores severly drop. Also I notice some jittering in the mouse, or trying to scroll down fast in a browser... which, according to what I've read, sounds just like basic symptoms of an unstable overclock.

I had started initially overclocking it far higher, to around 3.6 GHz, with boots, temps, and 8 hours of stress testing OK. I thought I had achieved a very successful overclock, but it was the 3DMark FPS that clued me that something was wrong.

Things I have tried:
I thought maybe it was the PCI-E bandwidth messing with the graphics card, although CPU-Z never said 1x instead of 16x. I tried setting the bandwidth to 100 and that did not help. I then set it back to auto, and tried increasing the RAM voltage to 1.9V. Did not help.
Before bringing the clock back down a notch, I went ahead and ran Memtest with the 400:801 set. I ran it overnight (about 7 hours) and had no errors.

I've heard of people getting to 3.6 and above with an E6750... Do I just need faster RAM? I know people clock their RAM faster than it's rated all the time, so I don't see how 1 Mhz over is causing the 3dmark score to immediately cut in half.

I'm pretty sure I've covered everything in excruciating detail, but if I'm forgetting anything, please let me know. Thank you!

[Janus67]

You may want to try changing the strap to the 400 one to see if it works for you.

[dEaFTOLiGhT]

I tried changing the strap to 400, which brought the RAM down to 800 MHz instead of 801. Still had the choppiness. I then set the strap back to auto, but this time adjusted the timings to 6-6-6-12 instead of 5-5-5-15 (rated).
So with the timings at CL6, went ahead and tried the 3Dmark benchmark again and it ran smoothly.

So now I figured lowering the timings would allow me to clock up the FSB, and in turn push the RAM clock above 800. I tried 420:841, and then ran the benchmark. Immediately I could see the huge performance drop, so I rebooted and tried pushing the RAM voltage to 1.9V, but that didn't help. Set it back to 1.8V, and brought the FSB down to 410:821, then 405:811, then 402:805, and finally 401:803. Every one of these had the same severely reduced performance in the benchmark.

Just now, I set it back to 400:801 (while maintaining the CL6 timings), which worked earlier as I had mentioned... and oddly enough, I had the same poor performance issue on this run. I did not expect that at all, being that it worked a couple of hours ago.

So to recap, with 5-5-5-15 or 6-6-6-18 timings, 399:799 runs the benchmark smoothly, and 400:801 or anything above cuts it in half.

I have no idea what is causing this!

[Janus67]

What voltage do you have going to the northbridge/MCH?

[dEaFTOLiGhT]

The NB voltage is set to Auto.

[redduc900]

What's the exact model of RAM installed? Temporarily remove 2 x 1GB modules, leaving the remaining two in a dual-channel config. (1st and 3rd slots), w/ the timings adjusted to their rated values of 5-5-5-15-2T (Command Rate; all sub-timings left on Auto) and 1.90V.

[dEaFTOLiGhT]

The model is 2x G.SKILL 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory Model F2-6400CL5D-2GBNQ

I'll give that a shot when I get home from work. I'm assuming you want me to keep it at the first notch that gives me the issue (400:801)?

[redduc900]

Take the FSB off the 400 strap line by adjusting it to > 401MHz, and leave the FSB Strap to NB at 333 for the time being. Also leave PCI-E frequency on Auto or 100MHz, NB and SB voltages on Auto, FSB Term. voltage (VTT) at 1.20V, and both Spread Spectrum options disabled. Leave all other voltages on Auto except for the DRAM voltage set to 1.90V, w/ the DRAM frequency set to 1:1 w/ the FSB.

[dEaFTOLiGhT]

Thank you for the suggestions... unfortunately, none of them worked. It's a pretty quick test. All I have to do is fire up 3DMark and run the benchmark, and all you need is a few seconds to see if the FPS is drastically reduced to about 1/3 of normal. And this happens no matter what whenever the RAM hits >800 MHz

[Janus67]

What cooler are you using?

[dEaFTOLiGhT]

Right now I'm using the stock cooler with AS5, but the temps are in the low 30s at idle and high 60s, sometimes hitting 70 at load. CoreTemp always reports a a couple degrees lower than HWMonitor and OpenHardwareMonitor.

I received my new cooler master hyper tx3 yesterday and am planning on installing it tonight or tomorrow. However, since the temps weren't going over 70, I didn't think that was causing the issue.

[dEaFTOLiGhT]

I ran some PC wizard benchmarks at 399 and 400, and posted a screenshot of all of them, in hopes that it might help:



Link to pic: http://twitpic.com/9evbjr

As you can see, only diminished performance on the CPU at 400 is the "Mandelbrot Parallelized." On the global benchmark, The Cache and Memory Performance, Memory Performance, and Video Performance drastically decrease. This is all with the 9800 GX2.

[Robmoo]

Generally Ram doesn't OC well. I couldn't run my Hyperx 2200 at its rated speed. Part of that could have been my VRM running at 78c.

[dEaFTOLiGhT]

Temporarily remove 2 x 1GB modules, leaving the remaining two in a dual-channel config. (1st and 3rd slots), w/ the timings adjusted to their rated values of 5-5-5-15-2T (Command Rate; all sub-timings left on Auto) and 1.90V.

Unfortunately, this did not work. Same result.

[dEaFTOLiGhT]

This is really interesting. Someone suggested it might be the 9800 GX2, because it has a dual-GPU setup and they can do strange things sometimes... like a GPU/memory subsystem problem.

In order to test this, I went ahead and swapped the 9800 gx2 for the 6570. I could get it up to 399:799, but as soon as I put it at 400:801, it wouldn't even post with that card. I would have to reset the CMOS or swap with the 9800GX2, which would post at that setting. I don't know if that helps.

[dEaFTOLiGhT]

bump... just seein if anyone has any other theories.

[dEaFTOLiGhT]

I just figured out for sure it's not the RAM. I set the RAM divider to 800, and set the FSB back to stock speed of 333, making the RAM run at 889 (333:889). The performance issue does not happen. So the RAM can be overclocked. So this means the performance issue with the graphics card only happens when the FSB is clocked to 400 and above. FSB<399, no graphics issue. FSB>=400, graphics performance issues and jittery computer. Does that shed any light on the issue?

[nursingZombie]

this is the reason i only use AMD anymore-- from what deaftolight stated, it sounds like a gpu bottlenecking problem with the ram... have you tried to swap out the video card or run stock video from your mobo and oc ram yet?

[dEaFTOLiGhT]

Yes, I have tried swapping, with an AMD card in fact. That wouldn't even post when FSB was set to 400.

In order to test this, I went ahead and swapped the 9800 gx2 for the 6570. I could get it up to 399:799, but as soon as I put it at 400:801, it wouldn't even post with that card. I would have to reset the CMOS or swap with the 9800GX2, which would post at that setting. I don't know if that helps.

[dEaFTOLiGhT]

I got around the problem! Finally!

It was the NB voltage the whole time. I set it to 1.4V manually, and the 3Dmark graphics card ran smoothly. After that I raised the FSB pretty high, to about 450, and got a BSOD. I jumped so high because before I noticed the graphics problem, I was passing stress tests around 3.6 GHz. My guess is without the NB voltage manually set, it probably never was really reaching that level. Because with the NB voltage set, as soon as I got in the 430 range, I needed to manually set vcore, as auto stopped working for that setting as well.

Anyway, I got my system stable at 440 with vcore set to 1.4850 if I can remember correctly, as I woke up to an orthos stress test with no errors. CoreTemp's max was in the high 60s, while HWMonitor's was 70 for both cores and RealTemp's 71. They always read higher than CoreTemp (and if anyone knows which one to trust the most, feel free to chime in). Thanks for all your help and input; I'm excited to see how much performance I can squeeze out of this thing. Now I'm gonna have to deal with figuring out when it's the CPU voltage, CPU PLL voltage, FSB termination voltage, NB voltage, or even if the RAM voltage needs to get just a tenth over rated for really high speeds.

I'm assuming that not getting the graphics error as I continue to OC doesn't rule out that I need to increase the NB voltage levels though, right?

P.S.
It's funny, I had never been so happy to see a BSOD before. The graphics card problem was preventing me from pushing the chip to anything that required voltage tweaking (>400 FSB). So I hadn't gotten one BSOD since I started OCing this thing. They started to **** me off right away on my way to a stable 3.520 Ghz, though. :-)