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PCB Design and Cooling System

Nvidia permits no experiments with PCBs of its premium-class graphics cards. That’s why the Gigabyte GV-3D1-7950-RH is nothing else but an ordinary GeForce 7950 GX2 manufactured by Foxconn for Nvidia and then shipped to Gigabyte.

Gigabyte’s stickers on the cooler’s casing and fan are the only things that differentiate this product from a reference GeForce 7950 GX2. Otherwise, this is the same two-storied design we described in our earlier review called Two for One: Nvidia's Dual-Chip GeForce 7950 GX2 Reviewed.

The graphics card consists of two PCBs combined into a single whole with four hex-headed poles. The PCBs each carries one Nvidia G71 chip, but they differ in other components. The bottom PCB is equipped with PCI Express x16 and MIO connectors and also carries a PCI Express x48 switch that distributes the available PCI Express lanes among the GPUs and makes the GeForce 7950 GX2 compatible with mainboards that do not officially support SLI technology. But in spite of that switch, there are only 64 mainboards on the compatibility list as yet. This is not much considering the total number of available mainboards with a PCI Express x16 slot.

The top PCB is simpler: besides the standard kit of one GPU and eight memory chips, it has a power circuit and a standard communication suite (two DVI-I connectors and one universal TV-Out/HDTV connector). It’s on the top PCB that the single (as opposed to the GeForce 7900 GX2) additional power connector is located. The PCBs are united into a single whole with a special two-section connector: one section transfers power and MIO signals and another, the longer one, transfers PCI Express x16 signals.

Each PCB carries eight 512Mb chips of GDDR2 (Samsung K4J52324QC-BC14), which give you a total of 1GB, but applications can only make use of 512MB, as on ordinary single-GPU top-end graphics cards. The memory and GPU are clocked at 600 (1200) MHz and 500MHz, respectively, in full compliance with the official GeForce 7950 GX2 specification. There have already appeared pre-overclocked versions of the GeForce 7950 GX2. Particularly, the XFX GeForce 7950 GX2 XXX Edition is clocked at 570MHz GPU and 775 (1550) MHz memory.

The Gigabyte GV-3D1-7950-RH is cooled with a couple of standard coolers the GeForce 7950 GX2 usually comes with. Using a copper core that contacts with the GPU die and a heat pipe built into the aluminum base for a uniform distribution of heat, the cooler ensures high cooling efficiency in spite of its small size and the small diameter of the fan. The G71 chip clocked at a rather low frequency of 500MHz doesn’t generate too much heat, and this helps the cooler, too.

There’s a layer of dark-gray thermal grease between the GPU and the cooler. The memory chips contact the cooler through elastic pads that consist of two halves with a layer of white thermal grease in between. The tight contact ensures good heat transfer.

Two 2.16W blowers, about 45mm in diameter, cool the heatsinks. They have a green LED highlighting, but it is not very bright and will hardly be visible in a system case with a side window.

The main problem with the standard cooling system of the GeForce 7950 GX2 is that the bottom cooler nearly touches the top PCB and obviously has problems getting enough air. The bottom GPU may overheat as a consequence, especially in a poorly ventilated system case. Installing a second GeForce 7950 GX2 to enable quad-SLI mode may aggravate the problem, so if you are going to build such a subsystem, you should purchase a large system case that permits to install additional fans.

Unfortunately, Gigabyte’s stickers don’t hold fast on the fans’ rotors. During our tests the sticker on the bottom fan of our card peeled off and stuck in the fan’s blades. With the two-storied card design, we couldn’t see the bottom cooler and didn’t spot the problem right away. The overheat protection system didn’t work for some reason, and the temperature of the bottom GPU grew up to a critical value. The system hung up, but the card survived, fortunately. We guess the PCB could have been as hot as 100-120°C near the GPU.

This is an example of what troubles a failure of the bottom cooler of your GeForce 7950 GX2 may provoke. We advise you to remove any stickers from the fans so that the described situation never occurred with your card. You should also check out and clean the card’s fans regularly to avoid problems and make the card’s life longer.

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