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Abit KT7A-R 5 volt rail mod?

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Old 07-30-01, 08:13 AM Thread Starter   #1
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Abit KT7A-R 5 volt rail mod?


Does anyone know what leg of which voltage regulator to connect 5v to?

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Old 07-30-01, 11:07 AM   #2
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Which 5 volt mod are you refering to?

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Old 07-30-01, 11:44 AM Thread Starter   #3
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Now that I think about it Hoot may have done this. For this mod you take a 5v line from the psu and connect it to a leg of one of the 6 regulators on the mobo to increase the current available to the cpu. It is supposed to add stability to a high overclock. The reason being is it was claimed that to much current is lost, most likely from the small size of the traces on the mobo to supply the cpu with enough power. I have only seen some rough descripions about it but never a pic or info on exactly where to solder the wire to. The mods for vcore and i/o voltage are well documented all over the place but not this one.

If I can figure it out and it does help then I will do a small howto on it . I gues I can get out my test meter and start probing around for a 5v feed to one of the regulators.

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Old 07-30-01, 12:11 PM   #4
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Okay, here is the link about the 5 volt rail mod:

http://www.icronticforums.com/showthread.php?s=45f686e84bdda0f54c6595695c6f3753& threadid=6357

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Old 07-30-01, 01:21 PM   #5
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Thanks HMOverclocker! There is also a mod to run 5 volts to the mosfet below the AGP slot. Some video cards pull so much current that the machine won't boot without the mod.

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Old 07-31-01, 05:29 AM   #6
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Interesting mod wish there where pictures as well.

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Old 07-31-01, 10:09 AM   #7
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Go to the link HMOveclocker posted to see the pics.

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Old 07-31-01, 10:37 AM Thread Starter   #8
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Thanks for the info and the link. That was just what I was looking for. I have been wondering about this mod for some time and wether or not it is worth trying. I may give it a shot but from what I read there could be 3 mosfets that would benefit from haveing 5v hooked up. Going to have to do some probing with a meter both before and after. Maybe I'll even clean the dust off of an old scope I have laying around as test meters don't show very short peaks and dips to well.

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Old 07-31-01, 10:48 AM   #9
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I am having an MSI K7T Turbo LE. Can I use this mod ?
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Old 07-31-01, 11:12 AM Thread Starter   #10
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Quote:
ºSåmuråiº (Jul 31, 2001 10:48 a.m.):
I am having an MSI K7T Turbo LE. Can I use this mod ?
Before even thinking about it monitor your voltages at idle and under load and see if there is a fluctuation. Then determine if your PSU has enough ooomph for the job. I don't know if this will work for your board heck I don't even know yet what it'll do for my KT7A-R.

You could always probe the mosfets with a meter to figure out where the 5v feed is.

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Old 07-31-01, 07:56 PM   #11
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I have 8 mosfets altogether. How do I check for the voltage using the voltmeter ?. There are 3 legs on the mosfets so which one should I be soldering onto ?
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Old 07-31-01, 09:30 PM Thread Starter   #12
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Usually it is the center leg that gets solderd.

What I have found to make the bigest differance in my KT7A-R's is good cooling of the mosfets. I have a Panflow 120mm intake fan in the left side of my case. It blows over the video card, ram, chipset, and mosfets. If I remove the side cover (and the fan) the mosfets heat up a lot and the system will start locking up on me. The next step I am going to do is AS epoxy sinks on all the mosfets and see if this makes any further changes in the voltage readings. Thre voltage must fluctuate more then normal when they run so hot and this could be the real problem and this mod is just throwing more juice to correct a overheating problem. If this is the case adding 5v would be a backwards solution when what may really be needed is just better cooling. I don't know if when these boards were designed that they were counting on cpu's that consume so much juice and the parts in the power supply just get to hot from the heavy load.

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Old 07-31-01, 10:42 PM   #13
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There are six mosfets, the bottom three provide three phase regulation of the 5 volt line for the other three mosfets that provide the Vcore. The bottom three mosfets only have 5 volts across them 1/3 of the time and they are there to clean up the 5 volt line before it gets converted to the Vcore. Running five volts to them all the time does not seem like a good idea as it defeats their purpose.

Perhaps a better idea would be to bypass the slow electrolytic caps with a small value fast cap like a tantalum. This would provide instant power instead of the slow ramp up that the electrolytic caps do. More of a square wave if you will. The benefits should be more constant voltage and increased stability.

As for cooling the mosfets, many of you are aware I have incorporated this into my last couple of boards. Take a look at the infrared photos of a KT7A at this link. When you open the link, click on the KT7-Raid. If you notice, the mosfets and the torroids are the hottest areas of a KT7 board. Pay particular attention to the bottom three mosfets, they are the 5 volt ones and they are also the hottest.

Here is how I cool the mosfets.


[img="http://albums.photopoint.com/j/View?u=1551335&a=11768501&p=51743929"]

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