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Changing Your CPU's Voltage

Date Written: August 8, 2000
Reviewed By:
Jason Rabel
Company URL: http://www.intel.com/


Need For Speed:

After reading the little voltage trick over at HardOCP on how to modify a Cel-II to get it started out at 1.65v, it made me start to think what I could do with my PIII-550. Let me give you a little background on why I did this mod then I will tell you what I was able to accomplish.

First, the board that I have my PIII-550 running in is a Soyo SY-7VCA that is an AWESOME board and pretty darn cheap (PCNUT has them for sale for $110), the only problem is that I got one of the very first boards (only like the first 20 boards shipped out had this problem they said) that was missing a resistor that somehow was related to the voltage tweak in the BIOS. Whenever I tried to up the voltage on the board the actual voltage wouldn't change & the system would become very unstable. So I always had to use the default voltage for the CPU (which for the PIII-550 is 1.6v). I was able to run about 141FSB (776Mhz) on it with a single 128MB DIMM, but when I stuck in two more (all 3 DIMM's now full with 128MB PC133) the system would only run stable at 133FSB (733Mhz). This was all fine and dandy, but after I say the article on HardOCP it made me start to wonder what I could do with my CPU. Well I went to the Intel website and found the spec's for the PIII's and here's what I found:


1 1 1 1 1.30
1 1 1 0 1.35
1 1 0 1 1.40
1 1 0 0 1.45
1 0 1 1 1.50
1 0 1 0 1.55
1 0 0 1 1.60
1 0 0 0 1.65
0 1 1 1 1.70
0 1 1 0 1.75
0 1 0 1 1.80
0 1 0 0 1.85
0 0 1 1 1.90
0 0 1 0 1.95
0 0 0 1 2.00
0 0 0 0 2.05
1 1 1 1 No Core
0 = Processor pin connected to VSS.
1 = Open on processor

The row in bold is where my CPU defaults to, pins VID0 & VID3 are open and pins VID1 & VID2 are connected. I wanted a voltage that would allow me to have a good gain in speed, but not create too much heat. I also was hoping to not have to modify the processor or motherboard any. Well, the only voltages I could of achieved on my CPU without any permanent modification would be 1.65v, 2.0v, or 2.05v. all of which weren't quite what I was looking for. So I opted to go for 1.75v, that's a good voltage for overclocking without needing monstrous cooling. I was planning on using a golden orb to cool the CPU (they are cheap & quiet!). 1.75v would require me to run power to VID1 & VID2 while cutting the power to VID0 & VID3. At first I was thinking I could pop apart the ZIF socket and remove the pins for 0 & 3, but when I tried to test this theory out on a slotket it proved much harder to do without damaging the ZIF socket. So the only other choice I had was to bend the pins for 0 & 3. I just took some needle- nose pliers and carefully bent the pins for VID0 & VID3 so they were out of the way. Then I took a piece of wire I had and stripped about 2 inches off the end, then I pulled out one strand from the core and used it to tie together VID0, VID3, and a (conveniently) nearby VSS. Check the diagram below (click on it for the complete picture), the connections that are red are the ones that I bent out of the way, and the green ones are the ones that I tied together to supply power.

So after I made this modification I carefully stuck it in my motherboard, I noticed that it didn't sit quite flat and that really bugged me. I didn't try using my Golden Orb for fear of breaking the CPU, so I used an Alpha FCPAL-35 that I had. I booted up the system and went to the BIOS, and sure enough it showed 1.75v!!! Yea!!! Well I went ahead and shot straight for 150FSB (825Mhz) (No guts no glory!) and set the memory for -33 (112FSB) because I knew all 3 wouldn't take 150FSB. System rebooted and windows loaded up! Yee Haw!!! So I went ahead and ran some tests and it was 100% stable!!! I tried for 154FSB but that was a no go, so I went back to 150FSB. I decided to run the RC5 client overnight and the next morning it was still crunching away and has been ever since. Not liking how the CPU wasn't sitting flush I decided since this motherboard was going to be the permanent home for this CPU I could clip the unused pins off and stick on the golden orb. Well I was about to cut the pins off when I remember how people have said how fragile they are so I tried to pull them off, and sure enough they popped right out and the CPU now sits flat in the socket. Here's a pic of the final CPU before I stuck it back in the board. (click for a larger pic)

So there you have it, this mod really works, for some CPU's it's a little more permanent than for others. But I am very happy because now I am running at 825Mhz rather than 733Mhz. If I was a little more daring I'm sure I could of set it for 1.80v and probably hit 154FSB or maybe even 160FSB, but that's really pushing it with the little golden orb and with it being in such a crammed case, and I didn't want all the other components running too far out of spec either.


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