Increased Voltage = More Unstable?

[alexsut43]

Hi all,

I've got a:
Core 2 Duo E8400
Asus P5KPL-AM motherboard
2 x 2GB xms2 Corsair RAM
GeForce 8800GTS

I'm pretty new to overclocking but so far i've step by step got my computer from 3GHz to 3.6GHz (400 x 9). But here i seem to have hit a wall... Increasing to 410, the system boots and is Prime95 stable for 1-2 hours, but if i then raise any of my voltages (individually or grouped) then my stability drops (Prime95 for 0-25mins)... Everything i've read suggests that increasing the voltage will increase the stability, especially at the voltages i'm using... I'm confused?

I'm pretty happy with 3.6GHz but i'm sure this system has more to give, its cool and still on low voltages, if i could figure out how!

I'm using SpeedFan, CPU-Z and Prime95 to monitor and test my system.
None of my bios settings are on auto.
My temps are: CPU 49 C and Motherboard 41 C under load

At 3.6GHz (over 12 hours Prime95 stable):
Vcore = 1.26 V
Vram = 1.85 V
Timings = 5,5,5,15
CPU VTT = 1.2 V
MCH = 1.4 V
ICH = 1.5 V

As far as i can tell my main limiting factor is my motherboard, it has a limited BIOS but still has a rated FSB of up to 1600, could exceeding this be causing the problem?

Motherboard BIOS options:

vCore auto/+50mv/+100mv/+150mv
vICH auto/1.5v/1.6v
vMCH auto/1.25v/1.40v
vDIMM auto/1.85v-2.24375v in 0.00625v increments
FSB 200-600MHz

Any suggestions of how to overclock my system further or an explanation of why increasing my voltages causes reduced stability would be greatly appreciated.

 

[alexsut43]

Sorry, maybe i wasn't very clear. I've got it stable at 400, but at 410 Prime95 fails with a rounding error after running for between 1-2 hours.

I've increased the voltages in an effort to make it stable at 410, but doing so just decreases the stability rather than increasing it as i would have expected...

 

[RJR]

You didn't say what ram you have, only timings set of 5-5-5-15. The only ones I could find in a quick search were the 1066 ram that require 2.1v. If this is the case, even if you have it underclocked, I would put a little more juice in the ram. You also didn't say at what speed your ram was running.

Also is this an E0 or C0 revision (stepping) processor? C0's will require a little more vcore and depending on the vdrop/vdroop of your board you may need more juice on the vcore.

 

[alexsut43]

The RAM i have is Corsair XMS2, i've got 2 GB sticks paired. 'TWIN2X4096-6400C5' on the Corsair website. It's built to run at 800 MHz at 1.9V with timings of 5-5-5-18.
My motherboard won't let me set the tRAS to 18 though so i've got it at the highest i can which is 15.
It's set at a 1:1 ratio with my CPU, so ~800 MHz...

Processor is the E0 version.

I've already tried stepping up the RAM voltage... its at 1.85 at the moment. With the CPU set at 410, Prime95 runs for about 1 hour 30. If i put the RAM voltage up to 1.9 V, Prime95 runs for 1 minute before detecting an error...

Same style with the CPU Voltage, increasing it +50mV (to 1.32 V) causes Prime 95 to detect an error after about 25 mins. Faster than with it at a lower voltage...

Keep the ideas coming though.

I'll try stepping it above 1.9 V and see what happens, Corsair say its fine up to 2.1 V so i'll keep pumping it and see what happens.

 

[RJR]

What Bios version are you using?


You may also want to lower your muliplier to 6-7 and up your FSB to see how far the ram will go. It should do better than 820 but you have to try and test to know for sure.

 

[alexsut43]

I'm using BIOS version 0502. Should be fairly up to date...

I tried lowering the multiplier to 6, but it didn't make any difference at all. it still failed after the same amount of time, so i figured it was not the CPU that was the limiting factor at the moment.

So to properly test the RAM I increased the multiplier from a previous stable state up to a RAM speed of 960MHz and its running fine. So it seems like its not the limiting factor either.

Could it be the motheroard FSB that is the limiting factor? It's rated to 1600 [O.C] but i thought it'd go a bit above... i've increased the NB voltage to 1.4 (the highest it'll go). Could it be that my motherboard just won't support a FSB over 1600?

 

[RJR]

The MB could be the thing thats holding you back. If the ram goes up to 960 Mhz without a problem, and your Bios is giving you limited options your probably going to have to settle for 3.6 Ghz. You may try to flash the latest Bios (0506) and see if you get any more options, but either way 3.6 isn't bad.