E6850 Asus P5K Overclock Qustions

[GHotep]

So, first off, I'm a n00b at this overclocking thing. I wasn't going to overclock, and then I started poking around in the BIOS, and I saw the FSB settings, and I raised it up a little, and then, well, here I am.

I wanted to get my E6850 stable at 3.6GHz air cooled. It looks like a popular speed, and I didn't think it'd be that tough to do. I have Corsair 6400 memory, so 400 FSB is not a problem there. I've spent the last couple of days tweaking, but I hit a speed bump.

I can set the FSB to 380, Vcore at 1.425 (in BIOS - under load, CPU-Z says 1.328), and everything is stable (11 hours Prime95 v25.3). Core Temp says 56, so there's plenty of margin there (I have an Asus Silent Knight for a cooler - again, I wasn't planning on OC originally, but my last system died an agonizing heat death, so I replaced the stock cooler when I built the system).

If I push the FSB up to 400, I have to set Vcore above 1.475 (in BIOS) to keep it from failing right away in Prime95. At 1.5V (in BIOS - drop/droop make that 1.392), I ran 23 minutes and Core Temp settled around 62C. Is this large of a voltage increase typical going from 380 to 400 (1.425 @ 380 is stable, 1.5 @ 400 isn't)?

A few other relevant settings - I have disabled spread spectrum for CPU and PCI-E (those were the only spread spectrum settings I found). I currently have the PLL set to default 1.50V, FSB set to 1.20V, and North Bridge set to 1.25V. Do raising any of those help in stability? And what's a "safe" limit (like the 1.55V Intel states for the E6850)?

Oh, and, if anyone made it this far (sorry it's such a long post) - I read somewhere that some Asus boards have a dead zone where it's hard to get stable clocks. Is the P5K (vanilla, not deluxe or anything) one of them?

Thanks is advance

 

[myocardia]

Wow, a new guy who knows what vdrop & vdroop are. I'm impressed. Oh, and welcome to anandtech. Whenever overclocking any component at all, YMMV*. It wouldn't hurt to try bumping your northbridge voltage a notch, but most likely you've just found the point of diminishing returns for your processor, regarding vcore/speed. The only way to find out for sure is to make sure your RAM is running 1:1, and try bumping your northbridge voltage a bit higher, and see if that makes any difference in stability.



*YMMV= your mileage may vary

 

[SerpentRoyal]

The nominal drop for an Intel DC is 0.04-0.05V. P5K is not a great overclocking board. You may be able to extract another 200MHz with a better board. I would be happy with 3.6GHz.

 

[GHotep]

@myocardia: Thanks for pointing me at NB voltage - I upped it one step (1.25 -> 1.40) and got 6 more minutes on P95 (29 minutes instead of 23). I have two more steps I can move it in BIOS (1.55 and 1.70), but I don't know what the chipset limitations are. I know the CPU has a max rating of 1.55, but I haven't seen the specs on the rest NB chips.

@SerpentRoyal: Right now, the fastest stable point I've found without really cranking Vcore is 380, which gives me 3.42GHz. Next time, I'll plan on getting a better board. Maybe I can come up with an excuse in the spring .

Are EVGA boards any good for mild OC'ing? My wife's E6750 / EVGA 650i board is waiting to get assembled once the case shows up.

 

[zephyrprime]

Your temps are too high. Even my pentium D 925 only hit 56c at 3.75GHz with an arctic cooler pro and stock voltage. You should be able to get much better temps than you are getting.

Lap your processor and your heatsink (if it needs it).

The p5k is not a great overclocking board primarily because of a lack of good cooling for the chipset but it should be able to hit 400 fsb easily.

These guys got it up to 490:
http://www.xbitlabs.com/articl.../asus-p5k_9.html#sect0

 

[MetaDFF]

There is a setting (not sure for P5K vanilla flavor has it, but Deluxe has it for sure) called "CPU Voltage Damper". If you enable it, it should help to reduce the Vdroop so it is not necessary to set such a high core voltage to compensate for the droop.

Hexus has a forum with some pretty good descriptions of the P5K BIOS options. You should check it out.
P5K Overclocking Guide

 

[GHotep]

Okay, a few more hours of tweaking, and I still can't get a stable system above 380MHz without pushing voltage up a ways and getting more heat in the cores than I want to see. I even tried 383MHz, with the FSB raised up to 1.40V, and it didn't quite make 3 1/2 hours. Since 380 / 1.425V Vcore is stable and the heat is much better (56C core after several hours), I think I'll leave well enough alone on this system and just plan on the next one being set up for better overclocking from the start.

@MetaDFF: P5K Vanilla has the CPU Voltage Damper. It was on Auto, I set it to Enabled at my 380 stable setting, and CPU-Z didn't report a voltage difference either at idle, or under load. I'll go take a look at the guide @ Hexus and see what it says.