Vmem voltage Radeon HD 6770

[itsakjt]

I want to volt mod my Sapphire Radeon HD 6770 graphics card. It has a copper base 2 heatpipe cooler. My current clocks are core at 970 MHz and memory at 1305 MHz. I want to increase the memory clock more. The picture of the back of the card is attached. Help is appreciated.

 

[Doctor Sid]

if anyone is still interested:
thanks to https://www.overclock.net/forum/188...715-sapphire-hd6450-gddr3-512mb-voltmods.html i think i figured it out.

it looks like this card comes with non-programmable VRMs, which means voltages can't be controlled by software or BIOS. in fact, i was not even able to get sensor readings for Vgpu and Vmem. some tools show a constant 1.000V, but that's obviously bullshit. so let's do a pencil mod!

here's the datasheet of the voltage controller used on this card (FP6329): http://www.hardwaresecrets.com/datasheets/FP6329.pdf
have a look at the "Typical Application Circuit": the resistor that controls the output voltage is the one between ground and the feedback pin. it's labeled "R2" in the schematic. the feedback pin of the IC is #6. start counting pins from the small dot on the packaging and go counter-clockwise (the physical layout is different than in the schematic - rely on the numbers only!).

you'll find this IC twice on the back of your card, one controls GPU voltage, the other one memory voltage.
now check all the tiny SMD resistors in proximity to the FP6329: you are looking for the one that has 0 resistance to pin 6 on one side and 0 resistance to ground (e.g. pin 3 or basically any blank metal on your case) on the other. then measure the resistance across this resistor (which will be the same as between pins 3 and 6). this is the value you want to reduce by covering it with graphite.

my stock measurements were ~1470 ohm for the Vgpu circuit and ~1010 for the Vmem circuit .

but first things first - what's the actual output voltage?
the output capacitors of the circuit make for a good measuring point and are usually easy to spot. measure the voltage across the capacitor (that is between the marked leg and ground). you'll have to do this measurement while the machine is running, so be careful as hell not to shorten any contacts with the probe!

my stock measurements were 1.13V for GPU and 1.60V for memory. this perfectly matches the 1.125 Vgpu i found in the specs, but i couldn't find any specs for Vmem.

time to apply some graphite!
do it in small increments and measure your results. in a first step i reduced the resistance in the GPU circuit to 1380 ohm, resulting in 1.21 volts. then tried 1250 ohm for 1.30V and 1210 for 1,38V. do the measurement immediately after powering up the system and hit the kill switch if you've gone too far. according to what i've read, it starts to get ballsy at ~1.3 volts for the GPU, although some are claiming to have gone up to 1.65 ( https://www.reddit.com/r/overclocking/comments/ds364m ).

disclaimer: these are my assumptions, don't take them for granted but check yourself!

 

[StaticVapour]

If anyone ever reads this thread, that Reddit post is mine and I indeed ran it at 1.58V. All I needed was told in RT8867 datasheet, the feedback line was somewhere under that ground wire I hooked up for trimmer. Found it by tracing the FB line from PWM controller.

That second picture is picture of stock voltage it was running. It was fun experiment but short lived, VRMs died pretty fast when running 1050Mhz with even more voltage. I even added small heatsinks to them but in the end I managed to kill it