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Cooling System

The efficiency of the reference GeForce 8800 GT cooler is questionable, especially when the GPU is clocked at an increased frequency. That’s why Gainward refused to install it on the Bliss 8800 GT 512MB GS GLH. This card comes with a unique cooler that differs greatly from everything we have seen so far. It resembles the reference cooler of the GeForce 7900 GTX, but with some special nuances such as the placement of the fan below the heatsink.

The main heat-dissipating element of the cooler is the massive aluminum heatsink with a large ribbing area. The GPU die contacts with a copper heat-spreader that has no ribbing of its own but is connected to the main heatsink by means of two copper heat pipes. There is a hole in the heatsink where the fan resides. The fan is sucking the air in through the ribs and blowing at the heat-spreader’s sole, the PCB, and the metallic plate that cools the memory chips.

This solution is arguable from an aerodynamics point of view. The air flow doesn’t cool the heatsink very efficiently, and the hot air is not exhausted out of the system case although there are slits in the mounting bracket that might be used for that purpose. The power circuit elements have a heatsink but the air flow doesn’t reach them.

Anyway, this system is going to be superior to the reference cooler due to the larger heat dissipation area as well as to the high-performance fan. It is also good that the fan is blowing directly at the PCB. The overall efficiency of the cooler depends on the quality of the heat pipes as well as on the thermal contact in the spots where the pipes are fastened to the sole and heatsink. That’s only true if there is a proper thermal contact between the cooler and the GPU, though.

The heat-spreader’s base that has contact with the GPU die is secured on the PCB with four screws. The cooler being rather heavy, it wouldn’t be right to let the heatsink hang freely on the heat pipes as it might damage the GPU. So, the heatsink is additionally fastened to the PCB with a casing and four more screws, two near the mounting bracket and two in the rear part of the PCB. This fastening mechanism ensures the necessary rigidity. The plate on the memory chips and the heatsink on the power circuit elements are fastened to the PCB separately. The fan uses a 4-pin connection with PWM-based resolution of speed. The speed controller is set to maintain a constant speed, though.

Alas, we had some problems with the cooler of our sample of the Bliss 8800 GT 512MB GS GLH. The heat-spreader proved to be not exactly flat, which resulted in poor contact with the GPU die and, consequently, in overheat. We suspected that after the card would hang up all the time during our tests, so we dismantled the cooler to check it out. The traces of thermal grease of the die and the cooler were uneven, and the thermal grease itself was dried up. The card would still hang up in 3D application even when we replaced the thermal grease. So, we had to polish the cooler off to achieve a proper contact with the GPU. Hopefully, this is only a problem of presale samples of the Bliss 8800 GT 512MB GS GLH because the cooling system developed by Gainward seems to have a high potential.

 
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