All you voltage gurus...

[dominick32]

I have successfully vmodded a P5B-Deluxe mobo for vcore, vmch, and vdroop.

I have a quick and easy question for you all. I have gotten pretty lazy and like to overclock on the fly using PLL or SetFSB on the windows xp desktop. So for more vcore on the fly I simply turn my 50k VR for the vcore modification. This method works great but..

I have done this on multiple occasions. Went from about 1.30 vcore booting windows, to adjusting resistance all the way up to 1.54 vcore just from turning the VR. Sometimes I get a little greedy and use the vcore mod as an overadjustment, rather than setting a higher voltage in the bios first. = Pure Lazyness. And two times I actually hit 0 kohm resistance on the 50k VR and the motherboard would produce a quick <1 second screech and simply shut down.

What is the cause of this mobo shutdown, and what does a VR actually do to the rig when set at 0 kOhms??? Could I be damaging anything or just triggering an auto-sensitivity shut down?

Thanks in advance Vmod gurus...

[Super Nade]

I'm not familiar with the mod you are talking about, but if you can tell me what chip you are modding and how, I can probably help you with the theory. :)

[dominick32]

I'm not familiar with the mod you are talking about, but if you can tell me what chip you are modding and how, I can probably help you with the theory. :)
Thanks for the response Nade.

I am more asking along the lines of: Why does a 50k potentiometer shutdown the motherboard on a Vcore voltage modication if 0kOhms is reached?

[Super Nade]

It depends on what leg of the FET is being shorted to ground. What you are doing is setting up a short ckt. That usually means all the current flows through the path of least resistance. Probably this might cause over-current protection to kick in and shut the board down. Alternatively, this would be akin to shorting the MB to ground, setting up a ground loop and OCP would probably kick in here as well.

I'm giving you a generic answer because I'm not aware of the specifics of your case. Hope this helps :)

[dominick32]

It depends on what leg of the FET is being shorted to ground. What you are doing is setting up a short ckt. That usually means all the current flows through the path of least resistance. Probably this might cause over-current protection to kick in and shut the board down. Alternatively, this would be akin to shorting the MB to ground, setting up a ground loop and OCP would probably kick in here as well.

I'm giving you a generic answer because I'm not aware of the specifics of your case. Hope this helps :)

Thats exactly what I am figuring happened. Even though, my vcore was only @ 1.50 volts (generally not that high) at maximum resistance I believe the 0k Ohm resistance some how triggers an over-current shutdown. Even though the current is well within motherboard maximum bios defaults of 1.70vcore..

Maybe Ross can chime in here as he has the same board as me with exactly the same vmods.

Thanks again,
Dom

[Super Nade]

Note that by 1.7V you are referring to the max voltage supported. It is related to current, but then that depends on the power draw of the subsystem (P=VI). What is the chip you are modding? Can you link me to a datasheet?

[dominick32]

Note that by 1.7V you are referring to the max voltage supported. It is related to current, but then that depends on the power draw of the subsystem (P=VI). What is the chip you are modding? Can you link me to a datasheet?
The best I can do is give you some information and pictures on the IC. It is a simple vcore mod:

http://img.oc.com.tw/8k0285/2006821172341783472953.jpeg

And this is my board with both Vcore and Vdroop mods:
http://img142.imageshack.us/img142/5246/p5bvoltmod001pr4.jpg

[Super Nade]

That is an Analog Device programmable 2 to 4 phase buck regulator.
http://www.analog.com/UploadedFiles/Data_Sheets/ADP3198.pdf

I'll have to take a look at it for any detailed answers you may want, but if you take a look at the datasheet, it says there is an in built SC protection. So when you short the resistor, it just shuts down. :)

[dominick32]

That is an Analog Device programmable 2 to 4 phase buck regulator.
http://www.analog.com/UploadedFiles/Data_Sheets/ADP3198.pdf

I'll have to take a look at it for any detailed answers you may want, but if you take a look at the datasheet, it says there is an in built SC protection. So when you short the resistor, it just shuts down. :)

Thats why OCF is the #1 community on the net. Thanks Nade!!! :beer:

[Super Nade]

Not a problem man. You could have done this as easily as I have. I should be thanking you as now I'm curious about all of this. I'd like to see how safe this is and if any improvements can be made. Do you have a link to the mod by any chance? I may even write up a mini-electronics tutorial to mod buck-regulators sometime next week. :beer:

[dominick32]

Not a problem man. You could have done this as easily as I have. I should be thanking you as now I'm curious about all of this. I'd like to see how safe this is and if any improvements can be made. Do you have a link to the mod by any chance? I may even write up a mini-electronics tutorial to mod buck-regulators sometime next week. :beer:

All I have is the Vdroop, Vcore, Vdimm, and VMCH solder points. Nothing more nothing less. I am a phase change OC'er and I basically solder my my vmods onto the motherboard. Power it up and play around with voltage. I do not go into specifics although I admire the amount of "research thinking" you put into these topics. I guess the true root of my question, you have answered. Basically figuring out why 1k ohm produced 1.54 vcore and a turning the resistance a hair less to 0k ohm shut down the motherboard.

Keep me posted on your findings if you continue the research.

Thanks again Nade.

[Super Nade]

Dom, I was scanning through the datasheet and I believe it would do you some good if you sinked that chip. It seems to get rather hot when operated out of spec. Can you confirm this for me by touching it with your hand when it is in operation?

Just be careful not to shor out anything by perspiring over the leads. :D

[dominick32]

Dom, I was scanning through the datasheet and I believe it would do you some good if you sinked that chip. It seems to get rather hot when operated out of spec. Can you confirm this for me by touching it with your hand when it is in operation?

Just be careful not to shor out anything by perspiring over the leads. :D

Call me crazy, or call yourself telepathic but I already did that immediately after the shutdown occured for the first time. I have 3 X 120MM Fans blowing in a very efficient configuration over and onto my mobo. (Its a benching rig with NO case) The chip was cool to the touch, probably from the big 75 CFM's blowing onto it.

But, the only real way to test this out will be when I start overclocking on phase again with 1.65v to 1.80v. Than I will re-examine for you.

[DvBoard]

You might think about sticking a low resistance resistor in series with that pot. That would allow you turn to it all the way down without completely shorting it to ground directly, yet if it's a small enough resistance it won't hurt your abilty to pull more voltage.

Just a thought. Your choice. I take no responsibility :p.

[dominick32]

You might think about sticking a low resistance resistor in series with that pot. That would allow you turn to it all the way down without completely shorting it to ground directly, yet if it's a small enough resistance it won't hurt your abilty to pull more voltage.

Just a thought. Your choice. I take no responsibility :p.

Thats actually a really good idea. Like a little 2.5k resistor. Any ill affects with this Nade?

[Super Nade]

It will prevent a short/shutdown, but that should be o.k. I think by low he mean sub kOhm, something like 100 Ohms. What value pot are you using?

[Navig]

By adding a standing safety resistor, you'll limit a little the overall adjustable range of voltage flowing thru the circuit.

Super Nade, if you want to have fun looking at what folks are doing to voltage regulators, just peek over at the xtremesystems forums with an eye out for hipro5, aw9d max and p5ds.

navig

[DvBoard]

By adding a standing safety resistor, you'll limit a little the overall adjustable range of voltage flowing thru the circuit.

Super Nade, if you want to have fun looking at what folks are doing to voltage regulators, just peek over at the xtremesystems forums with an eye out for hipro5, aw9d max and p5ds.

navig
This is true, but add a low enough value and the overall effect is very small. I was not sure of a value to suggest, therefore i did not suggest any. Nade's suggestion of 100 Ohm would likely work. .1kOhms shouldn't limit is pot too much, yet still allow the resistance to NOT reach zero, aka. direct short to ground.

[dominick32]

It will prevent a short/shutdown, but that should be o.k. I think by low he mean sub kOhm, something like 100 Ohms. What value pot are you using?

Thanks for all of the responses guys.
I am currently using a standard 50k VR for my the vcore mod.

[jonspd]

I would add in a 10ohm resistor so you never hit 0