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.