Extreme voltage mods – Travis Hayes
First off, I would like to give a big thanks to a couple guys here at the Forums for giving me help on a couple snags I came across. A new chap by the screen name Micr0mega helped me find the memory V-read point (overlooked it somehow) – good guy just entering the field of modding and also thanks to the electronic guru L337 M33P, which most of you already know (if you don’t, you should! very smart), who helped me on the over current mod I’ll be talking about later! And last but not least, thanks to THEFORUMISDOWN.com for all image files linked to this guide!
NOTE: I nor anyone here at Overclockers.com shall be held responsible for any damage done to your card by doing this mod! Any mod done will void the warranty of your card. Remember – Modding, if done correctly, is safe, but if done incorrectly, it could damage not only the card but possibly other components of you PC as well! So be careful and pay attention!
This guide consists of two different mods: First, a common volt mod for the memory IC and core IC, and second, a more extreme mod (preferably to be done by a professional) partially disabling the core’s over voltage protection!
For the first part of the mod you will need…
- Fine tipped soldering iron and solder
- Two foot of single strand thin gauge copper speaker wire
- Two 10K ohm variable resistant pots (preferably 15-20 turns for fine adjustment)
- Voltage meter
…with the card out of PC and power turned off!
First thing we will do is set our pots’ resistance to max 10K ohm. You will notice that the pots have three leads – one in the front, one in the middle and one in the rear. The one in the middle is ground; this is the one that will be taken and attached to the solder pad on card or screwed to a retainer screw in the case.
The other two pins are opposites, meaning if you set full resistance on the front pin, the other will have 0 resistance (which is bad)! So we want to cut one of the leads off so we don’t get them mixed up! The one we don’t cut off will used as our main lead to attach to the card!
To set the resistance, just set your voltage meter to 20K ohm and put the black lead to the middle lead on the pot and the red lead to the main lead (pin you didn’t cut off). Now just start turning the pot in either direction till you reach 10 K ohm. Once the resistance is set, cut your single strand copper wire into four 6″ pieces and attach one end of each wire to one end of the leads coming off of the pots.
Now we’re set to do the mod to our card!
The card I’m using is an Albatron fx5700 ultra, which uses the NVIDIA reference design! We want to locate the memory IC and core IC on the card – they are located on the back side! I have circled and labeled them in yellow on the pic below:
Circled in red are the voltage read points for each.
Please use these read points to document voltage on the core and memory before doing the mod. On my Albatron, the core voltage was 1.35v (2D mode), and the memory was 2.5v before the mod; after the mod, I have taken the core to 1.54v (2D mode) and 1.71v (3D mode) and the memory to 2.9v.
The controllers measure 5mm x 5mm and have pins on all sides. The memory controller can be distinguished from the core controller by the amount of pins each has – the memory controller has 16 pins (= 4 on each side) while the core controller has 32 pins (=8 on each side).
These controllers use a single feedback loop to sense and control output voltage to the core and memory. The voltage reading is taken by the FB pin of the controllers; if the voltage is too low, it tells the card to increase. If the voltage is too high, it tells the card to decrease. All we are going to do is simply trick the feedback into thinking it’s not getting enough voltage by using the 10k OHM pots and sending the signal to ground.
Now to locate the FB (feedback) pin for each controller: Here are the PDF files for them! Of course, the controllers are very small compared to previous controller, such as on the ti series card. So instead of attaching to the controller itself, we are going to attach to the last resistor in the feedback circuit. I have links for pics of solder points under each pdf file!
Memory controller (PDF HERE): ISL6529CR – look at page 1 and locate the FB pin; counting counter clockwise from the reference dot on the IC, it’s pin #9.
Core controller (PDF HERE): ISL6569ACR – look at page 2 FB is pin #7:
Now just take the ground lead wires from the pots and connect them to a ground solder pad on your card, or a retainer screw on your PC case. Plug the card into the pc and power it up!
Take a voltage reading upon turning the PC on to see what you new core and memory voltages are and adjust your pot one turn at a time from there for desired voltage. This mod alone has let me reach clock speeds of 760/1200 MHz – here are screen shots of 763/1120:
This mod is for the core only! The memory IC doesn’t have this protection there, for the memory voltage can be taken up till you fry the card! (I think anyway? I haven’t been over 2.9 v).
As far as over voltage protection on the fx5700 core, it uses a 5-bit digital VID (Voltage Identification code) to specify a DAC (Digital to Analog converter) reference voltage. The ISL6569A uses rDS(ON) sensing for channel current balance, active voltage positioning, and over-current protection. Output voltage is monitored by an internal differential remote sense amplifier. A high-bandwidth error amplifier drives the output voltage to match the programmed 5-bit DAC reference voltage.
The resulting compensation signal guides the creation of pulse width modulated (PWM) signals to control companion Intersil MOSFET drivers, which in turn control the upper and lower mosfets of this two channel converter. The upper mosfets on each channel send a voltage reading to an internal current sense; the voltage reading is averaged and then sent to the PWM (pulse width modulator) and compared to the DAC reference voltage. If the DAC and Current Sense don’t match within a certain range, the PWM sends a signal to the external mosfet drivers to turn off the upper mosfet and turn on the lower one.
Over-voltage protection is achieved by gating on the lower MOSFET of all phases to crowbar the output voltage. An optional second crowbar on VIN, formed with an external MOSFET or SCR gated by the OVP pin, is triggered when an over-voltage condition is detected. Under-voltage conditions are detected, but PWM operation is not disrupted. Over-current conditions cause a hiccup-mode response, as the controller repeatedly tries to restart. After a set number of failed start up attempts, the controller latches off. A power good logic signal indicates when the converter output is between the under voltage and over voltage thresholds.
However, looking again at the pdf file for the core, look at page 8 of the general block diagram. You will see the 2 Isen rails labeled Isen 1 and Isen 2 – notice the resistors Risen 1 and Risen 2, also seen in this pic:
Taking off these resistors and replacing them with resistors of a higher value will bring the sense voltage down, telling the PWM that the current levels are within specs, therefore not triggering the over current protection. My stock resistors are 2300 OHM surface mount – I replaced them with regular 2700 OHM (would have had to special order surface mount resistors and didn’t feel like waiting).
Anyway that’s a 17% increase in resistance. You can use a smaller resistor if desired, but I definitely wouldn’t go any higher; 2700 is enough; believe me, it let me take my core too 2.0 volts! The ideal resistor is 2500 OHM, but they are hard to find from what the guy at the repair shop told me. The 2500 OHM resistor should put you at around 1.80-1.89 volt trip range, which is good. However, if you do use the 2700 OHM resistor, as I have, it puts the trip range a bit over 2.0 volts.
So just be sure to keep an eye on the voltages when adjusting the pot. I noticed anything over 1.9 volts doesn’t seem to have any additional gain on core speeds. Remember, the core is 0.13 micron, so just make sure you have good cooling for the core (straight water cooling is good) if you are going to do this mod.
Here is pic of actual mod:
Good luck and enjoy!
Here’s what you have to look forward to! These are no record breakers, but it just shows you the stock clocks and 800/1200 MHz! Both benchmarks were taken back to back with same system specs – the only thing that was changed were the clock speeds!
Stock Clocks (3DMark03 Project Comparison):
800/1200 (3DMark03 Project Comparison):
If you have any questions, please feel free to contact me here at the Overclockers.com Forum or you can e-mail me!