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Stubborn 3800 X2 won't get prime95 stable past 2350MHz

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August 16, 2008 3:48:39 PM

I have an Athlon 64 3800+ X2 socket 939 I am trying to overclock. My motherboard is an Asus A8N-SLI Premium. I was using the AI Overclock set at 10% for a couple years rock solid, but I recently decided to push it farther. I can get it to boot into Windows as high as 2.6GHz, but it won't run Prime95. After some playing around I discovered that core 0 is the only one that crashes in Prime95. Core 1 will run all day long without breaking a sweat. Changing RAM timings and/or speed has a limited effect, if any. Does this mean I have a flaky cpu? It's Prime95 stable at my current settings below.

Athlon 64 3800+ X2 s939 E4 @ 2350MHz / 1.425v / HTT x4 (940MHz)
Asus A8N-SLI Premium
Corsair TwinX2048 C2 @ DDR470 (235MHz) / 2.5-3-3-6-1T / 2.75v
BFG GeForce 9800GTX OC
BFG 600w PSU
August 16, 2008 4:48:08 PM

What test type are you running with Prime95 that is crashing?

You have the E6 revision of the 3800+ X2 with default cpu multi of 12x and your currently running at 10x? Whats the temps?
The memory you have is PC3200 (DDR400)? (assuming so your getting a good OC at those timings now - though your voltage for DDR seems low - do you mean 2.75v?).

Also, what are the settings you use when you try to overclock to 2.6Ghz?
August 16, 2008 5:00:30 PM

Prime95 spits out rounding errors during the 1hr pre-test before crunching real data. It also errors out in the stress test mode.

The 3800 manchester is a 10x multi for 2ghz stock. The ram is of course DDR400. When I go any faster than what is now I increase the ram divider to 12 by decreasing the speed reference to 333. For example, a 240mhz FSB would yield 200MHz ram. But that 5mhz fsb difference is enough to create errors in prime95. I also adjust the HTT multiplier as necessary to keep it below 1ghz. I can't push the vcore past 1.5, and maxing it out doesn't help. Memtest86 always passes with flying colors no matter the speeds, as long as i keep it reasonable.

I forgot to mention idle temps hover around 35c. I haven't checked load temps because the newest nvidia monitor crashes on my system and I don't feel like rolling back to the old one.
August 16, 2008 5:16:28 PM

When you say 'stress' test for Prime I assume you mean the torture test (listed as that in my version). There are three vairants you can run: samll FFT, large FFT and blend. The first primarily stresses the cpu(s), the second mostly the cpu but some ram and the last alot more on the ram. I'm trying to understand which your running to see if we can get a hint as to a cpu or ram issue.

For actual DRAM freq, I use this formula (and verify with cpuz):
DRAM Clock = CPU Clock / (ceil(CPU Clock Multiplier/Memory Divider))
I don't have your mobo but my asus has the mem divider in BIOS as a ratio - does yours have that and what is it set to (or are you saying its just a single number - '12' - as you show above?).
What does cpuz say your mem is running at? (lets make sure its out of the equation as a source of the problem).

You've got to get something to check your load temps - idle temps don't mean anything for this.
August 16, 2008 5:27:58 PM

it's a shame 2.4Ghz is a sort of sweet spot.

my 3800x2 runs nice at 2.4
ht set to 600 gives 960
memory at 166 gives 200
Voltage on my Asrock 939n68pv-glan is at 1.4 (max it allows)
August 16, 2008 5:51:09 PM

OK i went back to the old ntune and checked temps while running two instances of prime95, one for each core (with affinity assigned). I let it run for about 20 minutes and temps peaked at 55c. That's a little higher than I thought it would be, but it still seems ok to me. I have a Thermaltake Blue Orb II with AS-5. As soon as I go to 240mhz fsb Prime95 errors in all three torture tests, BUT ONLY ON CORE 0.

For ram speeds, my bios lists ram speed according to ddr rate. I can choose from something like 200 to 400 in 33mhz increments. That actually sets the ratio or divider or whatever you want to call it. Leaving it at the default 400 translates to a 10 divider, while 333 is a 12 divider. CPU-Z is how I verified that. Here is what CPU-Z shows for my current settings.

DRAM Frequency: 235.3
FSB: DRAM: CPU/10
CL: 2.5
tRCD: 3
tRP: 3
tRAS: 6
tRC: 11
CR: 1T
DRAM Idel Timer: 16 clocks
August 16, 2008 6:14:18 PM

techw -
Yea, I was just reading your boards BIOS settings off the ASUS site. I understand what they do and agree with your math (my formula works using a 5:6 ratio which equals ddr333 - and divides the freq of the cpu by 12 when using a clock multipler of 10).
At 2400Mhz with ddr333 you'll be back at an actual dram speed of 400Mhz, which it can certainly handle.
But as a quick experiment you can try increasing the divider to see if it helps. I'd also try two other things to rule out the ram completely: run at CR: 2T and see if it works. If not, leave that temporarily and try uping the VDIMM. Depending on your actual Cosair modules you should be able to run at 2.8 and some support 2.9 (go up .5 at a time).
Likely though its the cpu - probably just reaching its max. You've got a 20% OC working which ain't bad.
You can try up'ing vcore if you're BIOS will let you - for the manchester core you should be able to safely go
to 1.5v (see http://wiki.extremeoverclocking.com/wiki/Image:VoltageC...). go up in the smallest increments the BIOS allows and check the temps (so far I agree with you that your temps sound good).
August 16, 2008 11:20:54 PM

I have been doing some more testing but I still can't get it as stable as I would like. Here is what I have it at right now.



It will run the Prime95 small FFT torture test for about 15 minutes before errors appear on core 0. The ram is running at DDR490 2.5-3-3-6-1T. :o  I let it do a couple full passes of memtest86 and surprisingly there were no errors. Temps approach 58c under full load with prime95 on both cores, but nothing else I do really stresses it that much so I'm gonna leave it alone for a while and see what happens. If I burn it up it's no big deal because I'm just gonna build a new computer in a month or two anyway.
August 17, 2008 12:48:23 AM

Well world of warcraft locked up at 2450 so I dropped it down to 2400 and it ran Prime95 torture test for over 40 minutes on both cores without error. Temp never went above 59c. I think I'll just leave it there, and pray it doesn't lock up again.
August 17, 2008 2:26:34 AM

It locked up again at 2.4ghz. I took back down to 2350 and it seems to be fine now. **** that pisses me off.
August 17, 2008 2:43:46 PM

Looking at some stuff on the net, both your chip and mobo can allow for better OC's.
But you might just be hitting a wall for your particular chip, ram and/or mobo.

In case you want to keep experimenting, here's a chart with some overclocks for the manchester for you to take a look at:
http://www.anandtech.com/cpuchipsets/showdoc.aspx?i=265...

Different mobo and ram then you but something to compare against and try. Increasing voltage to the chipset might be one thing you can try to see if it makes a difference.

Good luck!
August 17, 2008 3:00:45 PM

i'm not an overclock expert but from what i read (unless i missed the part) u havev't increased your Ram and Cpu voltages by +0.01

try to increase those voltages
August 17, 2008 10:24:16 PM

I probably didn't mention it, but I had the CPU voltage maxed out at 1.5v. My BIOS won't let me go any higher. The RAM is perfectly stable at 2.75v, and I have tried 2.8 as well. I may try 2.4ghz again with higher chipset voltage, but I don't expect that to work. I think there's just something wrong with core 0 on my CPU.
August 18, 2008 8:19:51 AM

panicatak said:
it's a shame 2.4Ghz is a sort of sweet spot.

my 3800x2 runs nice at 2.4
ht set to 600 gives 960
memory at 166 gives 200
Voltage on my Asrock 939n68pv-glan is at 1.4 (max it allows)


I ran my old X2 3800+Am2 @ 2.5ghz for almost a year and got it to boot at 2.7ghz. 2.4-2.5 is where it's at with that cpu, from my experience anyway.

EDIT: I had a guy help me fix something, when I didn't know how, and messed up something on my board. couldn't oc past 2.2ghz stable. the HT couldn't go anywhere near 800-1000mhz. I booted a little past 270FSB with the HTT set to x3. Good luck to you
October 7, 2008 6:29:08 PM

I have a 3800+ as well with an Asus A8N-SLI Board but your voltage is way too high, i was able to hit 2.5 ghz 24/7 stable on stock voltage 250 x 10 and set ht to 4x thats all i changed.
October 8, 2008 2:47:50 AM

I had the same X2 3800 but socket AM2.. on a MSI K9N SLI Plat board. I ran mine at 2.5ghz with HTT set at 600 and FSB@250mhz just fine for almost a year. I could run benchmarks at 2.7ghz but never tested if it was stable cuz i highly doubted it to be. It sounds like that one core is bad. It's too bad. It's a great chip, was my first dual core cpu.
Good luck to you
!