Going above 2.05V Vcore

[GigaFrog]

This is for Coppermines, but may apply to other CPUs.

1.Situation.

One of the way to get higher CPU frequencies is to increase the Vcore of the Processor. This of course, void the warranty and decreases the lifespan of the processor, but we already all know that (this is just a legal reminder).
Some (all?) i815 based motherboards will not allow the CPU to boot at other voltage than the CPU default voltage, around 1.7V for most Cumines (1.6 to 1.75V depending on version). This is known as the cold boot problem, and is solved by hard-wiring the voltage selection pins of the processor in a way that will force the Vcore at 2.05V (known as the wire trick).
I have being enjoying my higher overclock thanks to the clever overclockers than identified and solved the cold boot problem.

2. Limited to 2.05V.
Why not going higher than 2.05V (because it will void….)?
Once the wire trick is done, new settings appear in the BIOS:2.1V, 2.2V, 2.3V and 2.4V. The problem is selecting any of these results in a no-boot situation.
Why?

3. The VID pins of the Cumine.
If you have done the wire trick, you already are familiar with the VID pins of the Cumine. They are accessible in the back of the motherboard, in the CPU socket (or in the back of the CPU itself). Here is a shot:


And here, the same shot after the wire trick:


The Cumine has 4 VID pins, VID0 to VID3.
Now lets take a look at where these VID pins are going.

4. The Vcore regulator
According to what the VID pins are set to by the processor (or the overclocker!), the Vcore regulator will take action and generate the desired voltage.
On my CUSL2, the voltage regulator is the HIP6021. Here is the pinout of the device:



Notice something familiar? The VID pins actually set the voltage generated by the regulator. The weird thing is that there is one more VID pin: VID4.

The HIP6021 datasheet gives the VID code for each output voltage:



This is a table you probably all know also. The red setting is what the wire trick gives: all VID pins grounded.
Notice that all these settings (except the “no vcore”) are achieved with the VID4 pin grounded.
Now the datasheet also gives the following table:



All these settings can only be achieved with the new VID4 pin open.
Because the Cumine does not provide a VID4 pin, the motherboard will ground this pin. That is why no voltage higher than 2.05V can be achieved.

5. The solution: new voltages available

To overcome this limitation, you need to cut open the VID pins at the voltage regulator chip. Look for this chip on your motherboard, around the CPU socket and locate the VID pins. It is your choice to simply cut them or desolder and lift them (like I did) so that you can re-wire them to switches.
On my motherboard, I have a single switch, connected to VID0, VID2, VID3 and VID4. It allows me to toggle between 2.05V and 2.2V (the switch closes the pins to ground for 2.05V, and leave them opened for 2.2V).
If you choose the easy solution of cutting the pins, choose wisely which pin to cut to get the desired voltage. For example, cutting VID0, VID2, VID3 and VID4, and keeping VID1 soldered will lead to 2.2V (VID=11101). Once its cut, you can’t go back.

DO NOT CUT ONLY VID4: With the wire trick, this will lead to VID=10000, 3.5V. That will certainly fry your processor.

6. Incomplete boot?

You may experience incomplete boots after the mod, depending on your motherboard. On the CUSL2, the hardware monitor will stop the boot because it will detect an error (Vcore too high).
The solution is to go into the BIOS, and select hardware monitor. You will see the Vcore at 2.2V, that’s normal, and it will be written in red, signaling an error.
This is due to the fact that the BIOS is programmed to signal an error for a Vcore above 2.1V.
To overcome this, select “ignore” for the Vcore voltage.
After that, the boot will go all the way normally.

Note: this does not disable Vcore monitoring by Motherboard Monitor, as you can see in the annex of this document.

7. Hot Mosfets.

You may want to put a little heatsink or a fan of the Mosfets. As the CPU will drive more current, the MOSFETS (the switchers of the Vcore regulation circuitry) will get hotter.

8. Conclusion.

By doing the above “VID4 mod”, not only you risk damaging your motherboard if you don’t have good soldering skills, but even it you succeed, you will have significantly increased the stress on your processor.
I see it as the last little boost on an already old CPU, just to try to keep up …

I have a CUSL2, that works fine after doing this VID4 mod.
Even if you have a different motherboard, it is possible that you have the same Vcore regulator. If not, check the datasheet of yours on the net.

Annexe: MBM screenshots of my PIII "700" system

BEFORE:


AFTER:


Note: every time I unplugged my PSU, my BIOS resets (that explains the date 1/1/00). Probably a bad CMOS battery.

[Brad]

as I've said elsewhere, damned good article type thingee. I've got to find out how to do it to my vp6 now

[GigaFrog]

thanks Brad.
How come the pics are no longer visible? I messed up? sh...

Oh well, I can send the word doc to anyone who wants the complete article.

[iceheart]

That's nuts!

You need a title like "Nutty soldering iron man" or something.