Radeon X800 Non-Pro/X800 XL/X850 Voltmods

Author: Urlyin
Date: 2005-02-11 12:48:55


Overview- click on pic to enlarge

Above image gives us our vmod locations and points of reference. The blue Sapphire PCB #A474
has the same layout as the red ATI PCB, so it will work on all those models, no matter which manufacturer.
To the bottom right our arrow color code for the chips and measurement points, with the yellow arrow for our IGPU vmod.

As in the last article we'll start with the Pencil Vmod, along with the VID Vmod. The VID Vmod is something new to some of you and is the voltage identification code (VID) that sets the resistor divider for different output voltages. Which has been used by ATI since the 9800 PCB and by using 5 pins labeled VID0 to VID4 on the FAN5240 pins 7-11 are used to set the default voltage. With the VID table provided from the datasheet we can change the default voltage setting.

Tools and Supplies

  1. Digital Multimeter (a must have to complete mod safely)
  2. Magnifying Glass
  3. Electrical Tape (get the color that matches your PCB)
  4. 2b Pencil (works the best, found one at Staples in Drafting Department)
  5. Conductive Pen
It's easier to use Alcohol (99% Isopropyl Alcohol) and a Qtip to clean the graphite off the resistor. When I have brought the resistance down too low, I'll dab the dry end on the resistor a couple of times and recheck the Ohm reading. If it doesn't bring it back up to where I want it, I'll wet the other side of the Qtip with Alcohol to clean and restart.

Starting Prep Work

Before we get down to work, let's run through the multimeter to make sure we are on the same page.
You will be using two different settings. One to check the voltage before and after we make our changes. The second to check the resistance in Ohms of the resistors we're using our 2b pencil on, to safely lower their resistance to raise the voltage.
To check the voltage for the VCore and VMem starting measurements, set the multimeter to DCV 20V and to check Ohm resistance you'll set the meter to Ohms 2k or 20k depending on the resistor we're working with.

Measure GPU Voltage

Begin with writing down our starting voltages using the above pic, labeled Overview. Starting with locating the green arrow pointing to the capacitor close to the middle of the board labeled C60.
Now with the system running and the side cover off, visually inspect the area to first locate the capacitor and making sure there isn't anything in the way. Set your meter to DCV 20 V before placing the black lead of your meter on the screw holding in the video card, this is ground. Important when touching card with a meter lead that you don't accidently ground something out. Carefully place the red lead on the top side of capacitor C60 (you're upside down from the pic facing the card). Your meter should be reading around 1.40 V, cards vary from manufacturer to manufacturer. Write that VCore number down for future reference. There is not a measure point for the IGPU Vmod that I'm aware of at this time.

Measure Memory Voltage

Lets move to the VDD (VMem) & VDDQ measure points. In our Overview pic above, locate the green arrows pointing to our measure points, over to the left of the card labeled C1928 for the VDD and C1807 for the VDDQ. For a closer view click on the Overview pic to enlarge. With the same steps we used in the previous measure point. Place the black lead on ground carefully placing the red lead on the top side of C1928 (you're upsidedown from the pic facing the card). Your meter should be reading around 2.00 V. Record this as your default VDD voltage.

Now we are taking the last default voltage. Find the measure point in our Overview pic above, locate the green arrow pointing to capacitor C1807 for the VDDQ. Once more with the same steps as before place the black lead on ground carefully placing the red lead on the bottom side of C1807 (you're upside down from the pic facing the card). Your meter should be reading around 2.08 V. Write your VDDQ number down.

Now these numbers can be important in the Pencil Vmod and the VR Vmod. Before starting up the card, we can check the resistance to have an idea of what the starting voltage will be. Better safe than sorry and everyone should take care whenever vmodding, for the hardware and yourself.

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