|MSI R6870 Radeon HD 6870 Video Card|
|Reviews - Featured Reviews: Video Cards|
|Written by Bruce Normann|
|Friday, 05 November 2010|
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Closer Look: R6870-2PM2D1GD5
The MSI R6870-2PM2D1GD5 is a 100% reference card, and that's not a bad thing. To prove it, we're going to dig a little deeper than most, do some disassembly, and show you some of the tricks that AMD hid inside.
The first thing you notice when you pick up this video card is the dense construction of the entire assembly; it's heavy and feels solid. The single fan is a radial blower type, placed at the far end of the card, and the intake is a single round hole with a lightly beveled edge. I think AMD missed an opportunity to provide a relief cut in the profile, so that two cards in CrossFireX would have a decent sized gap between them near the fan opening. The fan only pulls air in through the main opening, there are no Batmobile air scoops, and once we look deeper inside we'll see why. The red stripes at the end are purely decorative, even though they hint that there are openings here.
The fan shroud isn't a completely sealed-off design; there is a small vent on the top near the I/O plate. We'll see later that some of the airflow is directed up to this outlet, it's not just an emergency relief vent. We will also see that there has been a major rearrangement of the layout, which avoids the dreaded overheating of the VRM section that plagued the HD 5870 reference design. After the air passes by the GPU and memory chips, it hits the voltage regulator modules, which have been relocated to the end opposite the blower wheel. After the GPU itself, these voltage regulator chips are the things that benefit the most from active cooling. My experience with GDDR5 memory so far, is that it runs pretty cool all by itself, and it doesn't need or benefit much from additional cooling. The fan is a PWM controlled design with a maximum speed of 4500 RPM, and the board supports the required 4-wire electrical connection.
With high-end video cards, the cooling system is an integral part of the performance envelope for the product. Make it run cooler, and you can make it run faster, has been the byword for achieving gaming-class performance with all recent GPUs. Even some midrange models have turned out to be supreme overclockers with enhanced cooling. The MSI R6870-2PM2D1GD5 has a fairly sophisticated design for its cooling device, comparable to the high-end reference designs released for the HD 5870 card last year. The thermal load for this new GPU is lower, so the size is smaller, but the design details and the construction quality are equivalent. The interior of the shroud reveals that some airflow is definitely ducted up to the vents at the top of the card, although a major portion makes its way out the I/O plate at the rear.
The layout of the various elements of the cooler design is a little easier to see in this straightforward view from the GPU's perspective. In addition to the contact patch for the GPU, the locations for interfacing with the DRAM chips and the VRM power chips are easy to see. There was good, even compression on the soft thermal tape used to equalize the surface heights of the various devices. The cutouts at the top and bottom near the blower wheel are for power supply components, which have a much taller footprint on the board. The same is true for the rectangular cutout near the end of the fin assembly, where the filter chokes and capacitors that supply the GPU are located.
Two 6mm and one 8mm diameter heatpipes are clamped between the thick copper mounting plate and the aluminum fin assembly, with the larger 8mm pipe passing directly over the center of the GPU die. Once they exit from there, they spread to the outer reaches of the aluminum fin assembly. Most heatpipe assemblies I've seen have used solder to firmly attach the pipes to the fins and the GPU interface plate. The solder also acts as a reasonably good heat conductor, and electronics manufacturers are intimately familiar with soldering things together, so it seemed like a good assembly technique. In this case, it looks like thermally conductive adhesive was used to connect all the parts. I don't know all the pros and cons yet, but we'll find out more as time goes on.
The copper mounting plate of this cooler is exceptionally thick, and large in plan view, too. This helps it to act more like a true heat-sink, where short heat pulses are absorbed quickly into the large thermal mass of the copper block, and the temperature of the GPU doesn't spike as high. To do this right, the heatsink has to have both high thermal mass and high thermal conductivity, and this large copper block qualifies on both counts. The thermal interface material (TIM) was very evenly distributed by the factory, but was applied slightly thicker than necessary. One day, anxious manufacturing engineers are going to figure out that too little TIM is better than too much. For the rest of us who end up correcting these things, a thorough discussion of best practices for applying TIM is available here. There is a raised portion in the center of the mounting block, and the remaining area is covered by a thin, clear protective insulating sheet.
The layout on the front and back of the printed circuit board is somewhat unusual in the arrangement of its power supply components. Most cards keep the current paths as short as possible by grouping the power supply and voltage regulator module sections somewhere between the power input connectors and the major electrical loads, which are the GPU and the memory modules. With the cooler design that this card has, in common with all the other radial blower designs, there is a dead spot directly behind the blower wheel where there is very little airflow. Unfortunately, this is exactly where the VRM section almost always ends up, and these components can generate some serious heat. The HD 6870 flips the VRM section over to the left side of the board, and makes the power come ¾ of the way down the length of the card and then do a U-turn before heading into the GPU. I can just see all the electrical engineers doing the face-palm.... Of course, they ultimately gave in, rather than redesigning everything after de-rating all the components due to the expected temps.
This new card from AMD is not as simple and cheap to produce as the GTX460 design, which is its current Fermi-based competitor. It's also not as compact, but it still runs cool and doesn't use as much power as its direct ATI rival, the HD 5850. It is however, simpler and less costly to produce than the GTX470, which is also its near neighbor in terms of performance, if not price. We'll have to wait for software voltage control and see if the GPU is worth all the effort that went into the design of the support systems.
In the next section, let's take a more detailed look at some of the new components on this reference board. I did a full tear-down, so we could see everything there is to see...