ATI 3850/3870 Voltmod thread

[quake6]

You must have done the mod wrong mine 3870 can handle over 1.9v without burning and i am using 100kohms

You set trimmer on max,100k ohm? And then how much was the voltage ?

[Riska]

At 100kohm it is about 1.38vgpu

You must have done something wrong

[Random Murderer]

At 100kohm it is about 1.38vgpu

You must have done something wrong

i'm thinking maybe he measure the wrong two points on the trimmer, so that when he thought he was at 100KΩ, he was actually at 0Ω

[Jaan]

Got Gigabyte HD3850 to mod- it has non-reference pcb with Nexsen PWM controllers on it.
Card has Zalman cooler and blue pcb, but I think same mods can be used for other cards with same PWM chip.
Vgu mods- I measured 10K resistance between GND and FB pin.
This is without mods!
Red line is connected to FB pin and any point of it can be used for "fooling" feedback voltage to chip.


Vmem mods- same story.


Actual mods on extra pcb:

and schematic diagram:

Voltage monitoring poins are knows already I think.
Mods working fine, Vgpu is limited at ca.1,75V with extra resistance on Vgpu, if you need more, use resistor with lower resistance.

[Random Murderer]

Got Gigabyte HD3850 to mod- it has non-reference pcb with Nexsen PWM controllers on it.
Card has Zalman cooler and blue pcb, but I think same mods can be used for other cards with same PWM chip.
Vgu mods- I measured 10K resistance between GND and FB pin.
This is without mods!
Red line is connected to FB pin and any point of it can be used for "fooling" feedback voltage to chip.


Vmem mods- same story.


Actual mods on extra pcb:

and schematic diagram:

Voltage monitoring poins are knows already I think.
Mods working fine, Vgpu is limited at ca.1,75V with extra resistance on Vgpu, if you need more, use resistor with lower resistance.

that's some ace-modding there!
NICE WORK!

[Viilutaja]

I am that lucky guy who got this mod on my Gigabyte HD 3850 512mb card.
Right now 860mhz on core is max what i get out with this "locked" bios. Without that mod and 1,256 v i got only 805 mhz max stable under benching. Memory is Hynix 1.4ns and right now i could get stable bench clocks with RTuner 1044mhz with stock vmem.

3DMark06 skore is 13568

http://service.futuremark.com/compare?3dm06=5461767
Not bad
Now in need of a good bios mod. So can go for 1000mhz.
And about temps. I have default Zalman cu700, bench temps i saw in load with RT monitoring were 81C. But those were with very high vcore, wich i just put on, knowing that those will be enough to pass with 860 core speed. Now try to lower them to optimize.

Thanks Jaan!

[Jimbo Mahoney]

the FB Pin is the Feedback it controls the Vcore on your card the pic is correct this is the Fb pin so now you have to find the resistor that is connected with the Fb pin on your 3850 for start and then i will tell you what to do

just take a multimeter and see witch resistor measures 0Ωhms with the FB pin

post a good pic of your card it will help us a lot

ok try measuring those resistor and see witch one shows 0Ωhms with the FB

if you cant put you multimeter prob on the FB pin because the are tiny you can put it on the capacitor that is connected to the FB see the trace line in the image that leaves the FB pin and goes on the tiny brown smd capacitor

I also have this same Triplex 3850 with 2415 PWM.

EDIT - I measure the resistance between the FB pin and ground (when the card is off ) and multiply by 20 (also seen 30 - 50 being used) to find the correct pot to use?

Thanks

[raibemunn]

could someone clarify what is that buzzing noise coming from video card when clock is big or framerates are high.
and is that dangerous if i can hear it almost all the time?

[Random Murderer]

could someone clarify what is that buzzing noise coming from video card when clock is big or framerates are high.
and is that dangerous if i can hear it almost all the time?

if it's loud, it is definitely something to be concerned about.
if not, it's just the noise of lots of power

[raibemunn]

well its producing that sound even with default clock and current (under load).
but now its pretty much constant when playing. how is one supposed to fix it?

[Random Murderer]

well its producing that sound even with default clock and current (under load).
but now its pretty much constant when playing. how is one supposed to fix it?

you have two options. rma it, or do a total recap.

[raibemunn]

Hynix mems have 1.834V by default. How much voltage could it handle and what do you guys think would be normal to run for 24/7.

[Jimbo Mahoney]

the FB Pin is the Feedback it controls the Vcore on your card the pic is correct this is the Fb pin so now you have to find the resistor that is connected with the Fb pin on your 3850 for start and then i will tell you what to do

just take a multimeter and see witch resistor measures 0Ωhms with the FB pin

post a good pic of your card it will help us a lot

ok try measuring those resistor and see witch one shows 0Ωhms with the FB

if you cant put you multimeter prob on the FB pin because the are tiny you can put it on the capacitor that is connected to the FB see the trace line in the image that leaves the FB pin and goes on the tiny brown smd capacitor

The third resistor down is connected to the FB pin.

FB pin to ground is 5.72k

Resistance of the actual resistor is 3.64k

[Vatos_locos]

Jimbo Mahoney try to shade with a pencil a bit the third resistor and see if the core can handle more Mhz if so then use a 100K Trim pot 25 turns from the FB to ground it souled work

raibemunn 2,2V souled be fine for DDR3 Mems

[Eldonko]

Random Murderer I saw you posted a pic of the blue pcb. I have HIS 3870 which uses blue and I have done the pencil mod, but I want to hard mod. Should I just add 100k trimmer to the pencil mod spot here or is there a better place?

[Riska]

Here u go.

[Eldonko]

Ok will do, thanks. I can use the ground to next to the VGPU read pt ya?

[ceemic]

This works to?

[Riska]

yes but it is way harder to solder there than the other spot

[Eldonko]

Which other spot are you referring to?

[ceemic]

My card: http://ceemic.pri.ee/hardware/hd3870/hd3870_13_1.jpg
Wanted to solder tomorrow morning. I don't know, if there is any other spot to solder...

[Random Murderer]

Random Murderer I saw you posted a pic of the blue pcb. I have HIS 3870 which uses blue and I have done the pencil mod, but I want to hard mod. Should I just add 100k trimmer to the pencil mod spot here or is there a better place?

Any of the green spots(they are all connected by a trace that i highlighted in green)

[ceemic]

Random Murderer, do You know any other spot to solder on my Giga's 3870? I have card here right now and DMM too, if it helps...

[Eldonko]

Very good, thank u sirs, will mod this weekend.

[Random Murderer]

Random Murderer, do You know any other spot to solder on my Giga's 3870? I have card here right now and DMM too, if it helps...

just got out of the shower, i would have posted sooner.
can you get a high res shot of the pwm area for me?