How to measure Vcore with a voltmeter?

[rustynator]

That is so true, also they could have made the measuring points slightly further away from each other on the board....my hands were shaking like a leaf. The measuring points are so small it felt like I was using a golf club as a probe.

[supershanks]

@rustynator -

....my hands were shaking like a leaf.

Hehe

Yessss I got an adrenalin rush checking out my mobo - my wife never understands these things :shake: (Mind you i don't tell her the risks.

 

The overvolting on vdimm seems pretty consistent. DFI NF4 board + High voltage memory? Read this!

 

@soundx98 -

Little deal labeled "Test Point" for us thick fingered types that a probe would make contact with easily.

very true but got a feeling there'd still be some1 who made arickets of it. :nod:

[rustynator]

I tried doing the reading using a molex as my grounding source. This gave on average a reading of 0.02V higher than the reading taken using the proper method. This is due to what supershanks mentioned....here is a bit of theory

 

Using the formula V=IxR, if the current (I) is kept constant by the power supply in the computer, and the resistance ® increases due to there being more wires and circuitry between the Vcore measuring point and the grounding point, the IxR will be a bigger value therefore V will be larger.

[supershanks]

rustynator,

yep your right no doubt about it, thats as soundx98 warned me of originally, i'm just confused that my readings were the same both ways.

This is my unit UT58C Digital Multimeter Used the 20 range for all except vcore when i swithced down to 2v.

[soundx98]

Oh good gawd. Don't let RedBeaver see that!

He'll buy, beg, or steal anything that is red.

 

There can also be contact resistance involved.

Ie; difference between 1st Molex on the lead and the last one.

Just a small difference in conductivity between the solder/crimp connection on the molexs' can make a difference.

 

This is from an old post by MBM5's author, Alex Van Kaam. (2003)

He is explaining that a difference of 0.00016v can result in a 0.02v difference in MBM5 readout (or any other software program).

 

Question: My Voltage is a bit off

Answer: Voltages are stored in the sensor chip as bytes, so a value between 0 and 255.

 

To get them into a number one must use a calculation, this calculation has to be the exact opposite of the way the board went from voltage to a byte value.

 

if the board maker does not stick to the exact specification in the sensor chip's datasheet then mbm will be a bit off.

 

An option you still have it to see if you can select another voltage configuration on the mbm voltage tab, this will effact all your voltage readout and there might be one that matches your board better.

 

Soundx98 Note: You can check this by changing/opening MBM5 settings - Voltages - and changing the "Voltage Configuration" from my config files default of "ITE8712F Standard 4" to "ITE8712F Standard 2" and watch the 12v line drop dramatically".

 

If your still out of luck you can make your own voltage configuration, simply open the voltage.ini file with notepad and start reading

 

how it's calculated example

 

the sensor chip retuns 106

 

MBM (and your bios): 106 * 0.016 = 1.694

 

0.016 has to be the exact opposite of what the resistors do (only if you made the board you know what it has to be exactly)

 

Since the sensor chip can only hold byte's you can have a situation where the value that goes from the resistors into the sensor chip is 106.49 = 106

 

even a very little 0.01 "real" voltage diffrence will cause the value in the sensor chip to go from 106 to 107

 

now with mbm (and your bios) that would mean

 

107 * 0.016 = 1.71 where it was 1.69

 

another way to look at it:

 

[real voltage 1.70384] / 0.016 = 106.49 = 106 in sensor chip * 0.016 = [voltage mbm 1.69]

 

[real voltage 1.70400] / 0.016 = 106.50 = 107 in sensor chip * 0.016 = [voltage mbm 1.71]

 

so a 0.0016 voltage change shows a 0.02 voltage change in mbm or any other program.

 

this also explains those voltage that seem to move or jump a lot

 

- Alex

Last edited by Alex van Kaam on 09-16-2003 at 06:00 AM

 

Sorry, don't mean to be droning on here

But how close can you get? Pretty frikken close!

 

Definately worth while to take the time and effort to measure.

If nothing else practice on the 3.3v, 5v, and 12v line.

[supershanks]

Hi soundx98,

Have seen something similar in the 12v Sag between idle & load. my idle Multimeter is 12.16v sensor = 185 so 12.16/185 = 0.06572973 now running @ load gives a MM reading of 12.13V a .03v sag this is to small a value for sensor to pick up, the sensor clicks down to 184 giving an reading of 184 x 0.06572973 = 12.09v so exagerating the sag.

 

luck

[CompGeek]

Holy crap, im reading 1.59v on the multimeter with my voltage set @ 1.55v and reading 1.5 in windows?!