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Another HD 5970 query

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New Member
Mar 11, 2012
I've had a HD 5970 for the past 1.5 years. On and off again I've tried overclocking the thing. Mostly just because I like to tinker with things... And in any case, I've now read a lot, lot, lot of info about overclocking just about everything humanly possible - so that's good, I guess.

OK. Here's my problem: I can't increase the gpu memory clock more than a smidgeon before the system becomes unstable.

The default values of core, memory and volt are: 725, 1000 and 1.05

By increasing the core voltage up to 1.1625 (via MSI Afterburner), I can get the core clock up to 875MHz and its very stable. However, if I go beyond 1050MHz for the memory clock (a modest increase of 5%), the benchmark test on FurMark freezes (1920x1080).

The temps look fine (the freezes come in usually between 75 - 80 C).

Everywhere I read about overclocking the HD 5970, people get the core clock up to about 900 (mine's within that range, so I'm satisfied) and the memory clock up to between 1200 and 1350!

So what's the deal? Can my card be messed up? Does this have to do with not being able to increase the memory voltage? Other people don't seem to be having any sort of issues regarding the memory clock.

The main game I play is Skyrim - and I'll admit that one reason I'm trying to OC the card is because Skyrim automatically set the performance to "high" instead of "ultra" when I installed the game.

My system is:
i7 950 @ 3.07 (not OC'd) with Antex 620 water cooling
Asus P6T deluxe v2
4GB x2 Corsair Dominator 1600 (in XMP profile)
Corsair HW 850 power supply
Corsair 80GB SSD in Sata2 as prime HD
Benq 23" monitor @ 1920 x 1080

All help/suggestions are appreciated!
Well, I guess I stumped the experts.

Eventually I decided that I don't care about FurMark or any other benchmark. The most stressfull game I play is Skyrim. So I use the following settings:

Core Voltage: 1162.5 mV
Core Clock: 900 MHz
Memory Clock: 1150 MHz

and so far, Skyrim is purring like a cat at Ultra settings. GPU temps top out at 70C. I'm happy.

However, if any of the experts think that the settings are damaging my gpu (particularly the Core Voltage), feel free to give me your advice.
Having a overclocked 5970 I can share these three nuggets of wisdom:

1. The GPU temp isn't really relevant on that card, especially when overvolting. The thing that overheats are the VRMs. My VRMs are usually around 30C higher than the GPU core temp. You can find the VRM temps with GPU-Z.

2. At least in my experience you must bump up memory voltage to be able to overclock the memory. I have mine at 1.15v.

3. When overclocking, make sure you are overclocking both the master and slave GPU equally. Otherwise you get pretty ugly micro-stuttering.
Thank you, thank you, thank you. A reply that I can use!!!!

If you, or anyone else, could humor me and fill me in on some info, I'd be much oblidged...

1. Voltage Regulator Modules, eh? What I have according to GPU-Z 0.5.9 is a smörgåsbord of temperature readings. I have separate values for:

GPU temperature
GPU Temp. #1
GPU Temp. #2
GPU Temp. #3
VDDC Phase #1 Temperature
VDDC Phase #2 Temperature
VDDC Phase #3 Temperature
VDDCI Phase #1 Temperature
VDDCI Phase #2 Temperature

At idle, all of these temps are within the range of 42C to 50C.

2. I would love to bump up memory voltage but MSI Afterburner doesn't allow this - only core voltage. Would you recommend ATI Overvolt Tool? AMD doesn't seem to like it anymore and it's not easily downloadable anymore. Is there another tool available?

3. I'm overclocking via Afterburner and it appears that both the GPUs are syched timing wise. The only thing that troubles me is that GPU-Z indicates that I'm in Crossfire (Enabled) mode if I look at the first (top) GPU. But if I switch to the second (lower) GPU, it says that Crossfire is disabled. Strange, but I don't know if it matters.

Anyway, thanks for the help!
1. VDDC Phase #1 through 3 are the VRMs for the selected GPU. There are three per GPU. For me the biggest overheater is VDDC Phase #1 on the master GPU, but I have an aftermarket cooler on my card so your mileage may vary. The VDDCIs are the two VRMs for the memory, although in my experience they don't overheat nearly as bad.

2. I used and overvolt tool that came with the card. I assume it was a skinned version of the ATI overvolt tool. I found that it worked fine, but it resets after every restart. Once I had found stable settings I ended up writing them to the GPU BIOS.

3. That is curious. It says I am Crossfire enabled for both for me.