Ultimate Underclock & Undervolt Project

Do-It-Yourself Systems
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System components

  • Enlight 7237 case
  • QuietPC 300W PSU
  • Asus A7V133 mainboard
  • AMD Athlon XP 1700+
  • 384MB PC133 SDRAM
  • Gainward GeForce4 Ti4200 64MB, AGP
  • 3COM 10/100 NIC, PCI
  • AverTV Studio TV tuner, PCI
  • Midiman Audiophile2496 soundcard, PCI
  • IBM 75GXP 7200rpm 30GB HDD
  • Plextor 12/10/32A burner

Fanless northbridge

Some things just don't need fans, but companies attach one anyway (to woo overclockers?) My Asus A7V133 motherboard came with an obscenely noisy fan atop the VIA KT133 Northbridge chip (4W chip power consumption). This was easily solved. I removed the fan, then detached the heatsink. I lapped the heatsink until it was flat and shiny, and lapped the Northbridge as well. Then I put some Arctic Silver II onto the Northbridge and reattached the heatsink. When I checked the temperatures I laughed: VIA's spec allows up to 110° C operating temps, above boiling point! I recall my sensor readings were in the 60's!

Under-volted Panaflo fans mod

Yes, fans get under-volted as well. This makes them spin slower, producing less noise. Guides on this are available on many websites. I am using two 80mm Panaflo L1A low-speed 1900RPM fans at 7V instead of default 12V. I did not choose 5V because the fans seemed to generate much less airflow than @7V. Even at 7V, the two fans are practically inaudible inside the case.

Athlon XP cooling mod

Alpha PEP66H heatsink with Panaflo blowing up towards PSU

When using quiet or passive cooling, it is crucial to maximize heat transfer by using high-quality heatsinks and thermal compound. I used a "new" Alpha PEP66H heatsink -- it has a copper base for drawing heat away from the CPU and aluminum fins to dissipate it into the air. I lapped the CPU and heatsink surfaces to shining point; then used a careful application of Arctic Silver II between them.

Then I used good ol' tape and attached one of the Panaflos directly underneath the Alpha, blowing upwards. The odd choice of position is no accident: the fan's purpose is to move all hot air upwards towards the PSU, where it can be sucked out by the other Panaflo acting as exhaust fan. This is the other golden rule of quiet cooling: fans must be placed strategically for maximum usefulness.

I unlocked the AthlonXP 1700+ by connecting L1 bridge contacts with conductive ink. Unlocking the CPU is crucial here, since you only want to underclock the CPU, not the FSB. Once I decided to go with 1.4GHz, I had to find the lowest voltage (read: lowest heat) at which the CPU remained 100% stable.

Power supply mod

Photo shows coverless PSY and both Panaflo fans

The PSU's maximum safe temperature is around 60° C, much lower than a CPU or video card. I started with a QuietPC 300-watt AMD-approved PSU; it has heatsinks for better heat dissipation. I removed the cover and replaced the default fan with my other 80mm Panaflo fan @7V. The cover would only obstruct airflow, and I needed this fan to remove exhaust air from the system as efficiently as possible, so the cover stayed off.


Hood geometry

To prevent a pocket of hot air from being trapped inside my case, I constructed a hood from thick poster carton. It forces air to flow from CPU heatsink to PSU and out of the case. I must note that it doesn't help much: CPU/motherboard temperatures went down 0.0-1.0° C when using it. However, I believe it keeps the front of the case cooler, i.e. the hard drive.

Hard drive

I am using an IBM 75GXP two-platter 30GB model inside a QuietPC SilentDrive enclosure; spinning noise is inaudible from a couple feet away. I also turned IBM's acoustic management to 75% quiet operation, at which point seeks are inaudible as well.

Fanless GeForce4: Fanless Mod

Here comes the fun part. The GeForce4 Titanium is NVIDIA's fastest videocard yet -- and unfortunately the hottest-running, which is why all of them ship with whiny high-speed fans. I got the Gainward Ti4200 64MB, because 4200 is the cheapest and coolest-running GeForce4 GPU. I also bought a "new" Alpha PAL6035 copper/aluminum heatsink along with Arctic Silver thermal adhesive.

I removed the stock HSF. Then I used sandpaper on a flat piece of glass to thoroughly lap the Alpha surface. Once it was perfectly flat, I put the sandpaper on the back of the Alpha and used it as a sanding block to lap the GPU. Once both mating surfaces were flawless, I proceeded to glue them with a thin layer of Arctic epoxy.

Fanless GeForce4: Voltage Mod

Unfortunately, the above mod was insufficient: my GeForce4 ran stable, but it reached a scalding 84° Celsius under load! Then I found an excellent article by Xbitlabs on GeForce3/4 voltage modification. While they talked about increasing voltage for better overclocking, I needed just the opposite -- to lower the voltage.

I noticed that my Gainward Ti4200 uses SC1102 voltage regulator chips (found on the backside of the board); the GPU regulator is the one near the metal mounting bracket. Xbitlabs posts its schematic here.

The voltage passed to the GPU equals 1.265 x (1 + R8 / R7) volts, so Xbitlabs added another resistor to R7 in parallel to reduce total resistance, thus increasing the R8/R7 ratio and increasing voltage. I needed to do the opposite, so I had to find R8 and add another resistor in parallel to it.

First I realized (from the diagram) that Pin 11 was directly connected to one side of R8; I just had to find where its other side was. I bought myself a multimeter and used it to measure the resistors on the board near the SC1102 chip. Ultimately, I found R8. See the pictures for the SC1102 chip and R8's two contacts A and B. I measured, by connecting to SC1102's Ground pin and point B on R8, that the default GPU voltage is 1.64V.

So here is the bottom line: to undervolt the GeForce4 you solder a resistor between points A and B in the diagram. You can use resistors from 22 to 100 Ohms for practical results. Here are the results I measured for those resistors:

Ohms Vcore Comments
0 1.64V -
100 1.43V -
47 1.40V, R8 removed my current setup
68 1.39V -
47 1.36V could still work at 250 MHz; but, occasional T&L errors
22 1.32V -

I'm rather new to soldering, and I eventually made a mess of my GeForce4 after trying several external resistors. I eventually broke off the original onboard R8 resistor and used simply my own 47-Ohm resistor instead of it. So now I'm at 1.40Vcore. Frankly, I'm amazed my videocard still works after all my clumsy experimentation :) (Editor's note: Those tiny surface mounted resistors are challenging even with a micro-tip soldering iron.)

Fanless GeForce4: BIOS Mod

Since I'm underclocking, I made my card believe 225 MHz (not 250 MHz) is its true speed. This eliminates the nuisance of using overclocking programs or CoolBits. I used the NVIDIA BIOS Editor and NVFLASH to extract and modify my card's BIOS. While at it, I added a cool boot message to signify my victory over heat.

Temperatures, Stability and Conclusions

Here are the results, with case cover on.

Stability is obviously not a problem, because I picked speed/voltage combinations that are 100% stable and error-free.

CPU temps were measured by the Asus socket thermal sensor. Please note that Asus readings are much higher (10-15° C higher) than other manufacturers' socket readings. This way, the readings better approximate true CPU temperatures. My CPU temp readings range from 57° C (idle) to 67° C (heavy load). The max allowable by AMD is 90° C, and I'm not anywhere close to that. Also, if I used VCool, my idle temps would go down but the worst-case temps wouldn't be affected.

GeForce4 temps were measured by a thermal sensor stuck between the heatsink and card, touching the GPU edgewise. The temps range from 64° (idle) to 68° C (heavy load). NVIDIA doesn't disclose the max allowable, but Anandtech's comparison of similar GeForce4 Ti4200 cards reported temperatures (under load) from 56° to 70° C -- using default speed and fan cooling! In other words, the fanless GeForce4 is entirely within spec, just 6-7% slower.

All of this proves that you don't have to give up high performance for quietness. Much better heatsinks, fans, and thermal compounds are available today than a few years back. Manufacturers are finally starting to realize that quietness matters; I purchased an AOpen H300A Slim Case for my server and the power supply uses a thermally-adjusted 80mm Yate Loon fan which runs at around 5V! Furthermore, this fan is positioned to suck air off the CPU heatsink, so the CPU gets cooled as well; I won't even need any modding.

The future is looking promising, but no need to wait: you can do any of the mods in this article right now.

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POSTSCRIPT July 28, 2002

After completing this article, I managed to destroy my GeForce4 accidentally while using the multimeter to measure GPU voltage. I shorted two contacts with the multimeter's pins while the card was powered up. Please note -- this was NOT caused by the modification itself, which proved perfectly safe/stable for something like 100 hours of 3D apps/games. However, if you are doing a similar project, my advice is not to take ANY electrical measurements on the card while it's running inside the PC. Lower temperatures will SAFELY reveal whether you succeeded lowering the voltage. The videocard died nobly for the cause of science - a moment of silence, please.

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