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AC Twin Turbo VRM heatsink compatibility fail on HD4850

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#1
AC Twin Turbo heatsink compatibility fail on Sapphire HD4850 reference model

This is for the people who are considering installing an Arctic Cooling Twin Turbo After market cooler on their card.
To show it's not as simple as, remove, clean and attach.
This maybe the same issue for the S1 coolers if AC supply's the same heatsinks which I assume they do.

I only noticed this serious issue after randomly taking out my card again for a double check expecting a losse RAMsink but to my surprise it was one of the VRM heatsinks which had become half detached.

Installation:-
AC does state this cooler will fit to the listed cards no problems which is not entirely true.
Yes the cooler does fit without hassle.
The RAM sinks and VRM sinks included DO require modifying.

VGA heatsink attached, no hassles here as long as you read the instructions.


Already known issue and documented on youtube installations is one RAM sink coming in contact with one of the copper heatpipes:-

This is very easy to correct, as seen here, all I did was get a standard set of pliers and bend in the fins a few mm.
Some people bend the fins various ways for it to or just buy a pack of extra RAM sinks.

The undocumented issue which I found out is with one of the VRM heatsinks
On some HD4850 cards (like on my Sapphire reference model) one of the resistors is a mm higher than the VRMs as seen circled here:-


The issue is this makes it impossible for the heatsink to sit flush on all the VRMs it's supposed to be cooling.
I should have noticed this when I found the other VRM heatsinks were sticking better.

Here is a pic with the contact imprints circled of the little contact made with the VRM heatsink to VRMs:-

As you can see only one of the VRMs is getting some contact while the other is getting none.
On the very right is where the resistor is making contact, causing the issue.
Below is the modification done with a small hacksaw and some frustration (reason why the after photo is so shakey LOL)

After this, I removed the old and not very adhesive thermal tape, replacing it with some fresh and actually adhesive thermal tape from work.

So there you have it.
Before you install ANY aftermarket cooler, make sure you read up ad research other peoples fails (like mine), regardless of what the manufacturer states the cooler will fit.
 
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#2
I went through most of these problems with Twin Turbo also on 4870 and 4890.
This cooler is also struggling to keep 4890 cool. It's enough, but barely.
 

newtekie1

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#3
Why can't you just move the VRM heatsink a little off center so it doesn't hit the resistor?
 
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#4
@robal
I just thought this should be made public as any consumer would expect all the new components to fit without physical modification.

It's only when you go to the Arctic Cooling website and look up support that they mention there is a compatibility with the 4xxx cards.

People who are new to this are probably thinking WTF when they see the fans are not spinning on the card and the temperature is rising only to find one of them piddling along only to find out software is the only answer given.

I decided to edit the GPU BIOS and adjust the fan settings in RBE.
Works great now.

Why can't you just move the VRM heatsink a little off center so it doesn't hit the resistor?
It's not possible to move the VRM heatsink across any further as there is another VRM heatsink right next to it.

I have also recently used RBE to edit the fan speed of the GPU BIOS so the fans run without need of software.
 

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#5
It's not possible to move the VRM heatsink across any further as there is another VRM heatsink right next to it.
And that one can't move over either?
 
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#6
And that one can't move over either?
The other VRM cooler has a resistor on the other side of it too which was a mm higher than the VRMs, just not as close as the other side which caused issue with the mounting of the VRM cooler.
 
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newtekie1

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#7
The other VRM cooler has a resistor on the other side of it too which was a mm higher than the VRMs, just not as close as the other side which caused issue with the mounting of the VRM cooler.
Ah, makes sense, I was just curious. Some pics without the main heatsink might be a little more helpful with people understanding the issues.
 
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Case Corsair Obsidian 650D
Audio Device(s) Infrasonic Quartet
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Software Windows 7 64bit and Windows XP Home
Benchmark Scores 2cm mark on bench with a razor blade.
#8
Ah, makes sense, I was just curious. Some pics without the main heatsink might be a little more helpful with people understanding the issues.
The issues are understood when you put the VRM cooler on.
But you can only trust by what I have said or see for yourself.

Personally the picture says it all.

Recently, I did find a thread at PCstats of a person who had the same issue with the VRM cooler.
He also had a Sapphire HD4850 reference model.
So this maybe only linked to the Sapphire reference models as Arctic Cooling have not stated an issue with their RAM/VRM cooler install diagram on their site which only shows up for the Twin Turbo.