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I5 750 - New Voltage Specs!?

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a b à CPUs
June 30, 2010 4:13:10 PM

Hi everyone. I've had my i5 750 for a couple months now. One of the first things I did was try to OC it, so I became familiar with the Intel documentation (http://www.intel.com/design/corei5/documentation.htm)

Perhaps the most important page was section 7.8 Absolute Maximum and Minimum Voltages - which I know for a fact were labelled as 1.55V Vcore and 1.21V Vtt. As reference here's a thread on it http://forums.anandtech.com/showthread.php?t=332659.

So recently it came up in a thread (thanks to cromedome for pointing it out) that the max is 1.40V. I just went to the check the documentation for myself and sure enough, they have the Vtt AND the Vcore max BOTH at 1.40V. Also, the very first page lists the documentation as JUNE 2010.

So what's the deal? Is it a typo? Why are the specs different now? I burned out an MSI mobo at 1.28V Vtt and I think that these specs are too high but hey maybe not. I'm curious what the people here at Tom's forums think about this.

More about : 750 voltage specs

a b à CPUs
June 30, 2010 5:11:23 PM

I have always needed 1.29 /1.31 for VTT on my p55 ud4p board over 3800 mhz, which took my ram closer to 1600mhz. With less, I would get spontaneous reboots.
IMHO, your MSI board, might have failed for other reasons. I know you have deduced that setting as possibly the only thing you were 'doing wrong'. But it might just have been the old, act of God :) 
Over at OCZ support forums, the reps have always recommended up to 1.35 vtt , on both p55 and x58 boards , attempting to get ram stable. I am not saying that makes it right or ok, just a observation. I also think that Voltage setting poses a threat to the cpu as much as your m/b.
a b à CPUs
June 30, 2010 5:33:28 PM

Yeah, I do agree the MSI board was probably just bad. The tech at the store who replaced it for me (with an ASUS :D ) said they were getting quite a few MSI returns/replacements so sounds like they're quality is just not up to par right now.

I also have seen that higher vtt being recommended, but the Intel spec sheet definitely said their highest absolute max was 1.21V Vtt. I find it very odd that they would revamp the documentation and raise it so much, to 1.40V. They also lowered the Vcore from 1.55 to 1.40V.

My CPU is stable right now at 175 base clock with turbo on, and my 1600mhz CL8 RAM at 1400mhz CL7. Voltages are Vcore 1.306V and Vtt 1.206V. I might fool around with OCing again just for fun (to see how fast I can get the RAM at CL7) which would need to go over the old Vtt spec... but, apparently, is now actually within spec.

Also, the i7 900 series Intel Specs (http://download.intel.com/design/processor/datashts/320...) dated February 2010 show max Vcore of 1.55V and Max Vtt of 1.35V. So how does the i5 750/i7 800 series max Vtt jump from 0.14V below 900 series to 0.05V above it? The previous Vcores were identical, but now i5 750 is lowered... I just find this so wierd... like it is a mistake...

EDIT: Just read the old sticky here on toms about OCing i5/i7s:
http://www.tomshardware.com/forum/256144-29-1156-core-o...
quoted:
"Maximum/absolute Maximum voltage by Intel: Vcore= 1.40/1.551.40, Vtt= 1.155/1.211.40, Vram= 1.575/1.651.80, PLL= 1.89/1.98"
and
"UPDATES:
28June10:
- Absolute Maximum Vcore, Vtt, and Vram change in latest Intel datasheet revision!"

I guess I'm thinking about it too much, but it does bother me that they can go and change it so drastically and also that this isn't really big news (although as pointed out, OC guides completely ignored the Intel Specs to begin with, recommending ~1.35V Vtt)
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a b à CPUs
June 30, 2010 6:19:44 PM

Well their might have been some extra caution, because of the witchhunt around burnt sockets at the launch of the 1156/p55 platform. Combination of The i5 750 o/c so well , out of the gate, the beta bios's on early test boards. Some hardware blew up, lol. ASRock was the worst culprit, and they supposedly made adjustments in the bios to sense and stop the phenomenon.

a b à CPUs
June 30, 2010 6:35:13 PM

Ah interesting. I only really got involved in all this over the last few months so all the initial release stuff I don't know about. I guess it makes some sense, particularily when the i7 9xx series had higher specs but the chips are so similar. Even so with regards to raising the Vtt, why did they lower the Vcore?
a b à CPUs
June 30, 2010 6:51:14 PM

wolfram23 said:
why did they lower the Vcore?

Due to the socket burn under extreme OC with LN2.
a b à CPUs
June 30, 2010 6:56:24 PM

Read this

http://www.anandtech.com/show/2859
Quote:
processor was overclocked up to 5.19GHz using our cascade with a -102° Celsius evaporator head temperature under full-load. Processor VCC power draw at these frequencies is around 160W (this is possible only due to subzero cooling), as measured with a clamp meter installed at the 12V EPS power lead.

Quote:
The random level of pin/pad contact in the VCC/VSS area is an accident waiting to happen when the processor begins to draw current, especially when highly overclocked.
a b à CPUs
July 1, 2010 1:15:49 PM

After reading that article, I don't think that they insulated the socket properly. Petroleum jelly needs to be put in the socket under the CPU to prevent moisture from getting there and doing that same thing when using extreme cooling.

The random pin contact definitely wouldn't help, but I don't think that's the main cause of the burns.
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