Starting the easy way. Radeon 7000 with linear regulator.

Hi mates!

I'm starting to voltmod all my AGP cards to benchmark seriously on them (enthusiast league, watercooled) and I've decided to start with the Radeon 7000 64MB DDR.

Why this one? Well, because the main VR is linear, and as such, the power circuitry is extremely simple. A couple of resistors and a couple of capacitors, besides from the Nikos L1084S adjustable low dropout regulator.


Here's a pic of the board area, and the extracted circuitry.






So, tracing down the resistors and the pins, I've come to conclusion that I have to modify the 68X(R895, 50Ohm) marked resistor and add a pot in series with it.

Calculating, seems that the regulator is set at 1.88V, but will real-world measure that when the motherboard arrives. If I increase said resistor from its stock 50Ohm to 60Ohm, vCore gets boosted to 2V according to my math, and the increase seems to be linear with the resistance rise. In that case, a 20-ish ohm pot would be more than enough for my vcore needs.


Are my assumptions/observations right?


Thanks for the help in advance!

So, does this thing operate at 3.75V?!

It must be manufactured in a very big process then O__O


I'll go grab a pot tomorrow and see what happens edit: Waaait... 2k~ I have on the components drawer


By the way, gonna put together an ancient Sempron rig I must have somewhere in my room and measure how's the Vcore in real-world.


Thanks!
Edited by Artikbot - 2/26/12 at 4:21am

Uh! Forgot about this thread!!

Anyway, here's the tests:

The regulator gets juice from the 3.3V rail, so it means it can't output 3.75V.

I plugged the card and measured the voltage. It indeed outputs lower than that. Working voltage is 1.88V, measured at a random point in the ground plane and the tab of the regulator.
That has a lot more of sense

Since the card overclocks so bad it won't be of any use in benchmarking (also discovered it's a 32MB, so I have zero chances ), I'm gonna go ahead and experiment with it, and see if I can successfully mod it.

Currently searching where does the VRAM get fed from, seemingly it's from that N-MOSFET upmost of the board, voltage at Source pin reads 2.48V.

The input voltage of that MOSFET is 3.35V, and gate is driven by a nearby transistor (update- it's a shunt regulator, not a transistor).

Being that said, I have absolutely no idea on how to modify the memory power circuitry. Basically because I don't know how do shunt regulators work



Edit: Just soldered the pot to the 50ohm resistor from the GPU regulator.

If I decrease the pot value, the voltage goes down!!



Edit2: Just soldered the pot to R894 instead, and BAM! 2.31V

Worth mentioning I shut it down. Soldering a bigger pot as we speak. Don't wanna fry the board, at least not yet!!

Good news is, it booted up even at those volts.


Edit 3: While de-soldering R895 I accidentally broke it, and had to swap it with a 1/4W resistor. Works now, voltage's back to 1.85!

Let's see if the 47K pot on R894 has done something useful


Edit 4: Success!! Adding a pot in parallel with R894 DID increase Vcore! But I lowered the value from 47 to 2K, for better accuracy. Right now it sits at 3/4 (single turn pot), and vCore rests at 1.92V.

I've effectively bumped corespeed from 315 to 340 and zero artifacts!!

I'm doing a decent post so everyone can udnerstand and do this easy mod
Edited by Artikbot - 3/11/12 at 10:33am

So, to sum it up.


You'll need this:

-A fine tip soldering iron. I use a JBC 35W with a T05D tip.
-Soldering tin, obviously.
-A 2KOhm variable resistor, multiturn is recommended, but I'll do it with a single turn. This card isn't cutting edge tech, so there's no need for pinpoint accurate components.
-A multimeter that can read on a ~2V scale, accurate to the millivolt.
-A steady hand.


Okay, first of all, this mod is only likely to work with this particular kind of PCB. You might be able to reproduce it on other cards, as most of them share a 5A, low dropout linear regulator as a way to feed the core.

Please note I'm not responsible of any damage that might occur due to doing this mod!!

Grab your card and locate resistors R895 and R894. They are near the NIKOS L1084S regulator.

Now pick a couple of cables and solder them to the terminals of R894. Then, solder the cables to the variable resistor, and glue it/place it wherever you want.



Ta-dah! Done



Mind the other pair of cables going from R895, I disintegrated that one while figuring out how to do the mod, so I had to replace it.

The lower the resistance you set on the VR, the higher the Vcore will be. At a near-shorted resistor (5Ohm or so) vCore will be 2.3-2.35V, the maximum the regulator will allow (due to internal drop).
With the VR set at maximum value (2K) vGPU measured at the regulator tab should be around 1.83-1.84V.


Have fun! Meanwhile I'll figure how to do the vRAM mod.