Microsoft Corp. has logged a huge 1.06 billion USD (130 billion yen) charge due to warranty claims for its "Xbox 360" game console. This is a frightening amount of money for engineers engaged in product design.

Amid current circumstances, where consumer electronics manufacturers often recall their products, this is no longer someone else's affair. We would definitely like to know what caused Microsoft to log such a large cost.

Microsoft itself, however, refuses to reveal details of the malfunction that has forced the company incur huge expenses. So, we can only investigate the cause by ourselves. Nikkei Electronics thereby attempted to analyze the Xbox 360's heat radiation system, having a thermal design expert cooperate.

Nikkei Electronics focused on the heat radiation system for two reasons. One is that the Xbox 360 is known as a game console that often goes thermorunaway.

The other is that some have reported they heard a snapping noise when the Xbox 360 broke down and became inoperative. This makes sense if a component broke due to heat load caused by insufficient heat radiation.

We prepared two units of the Xbox 360 for analysis. One is the Xbox 360 the IT Pro editorial office purchased at the end of 2005. The other is a personal property of a reporter in the IT Pro editorial office who is also a heavy gamer.

The latter one had the same malfunction reported in this time and was repaired in May 2007. We considered we could probably discover the cause of the malfunction by comparing these two units, if Microsoft had implemented new measures to discharge heat when repairing the broken unit.

The heat sink for the graphics LSI is smaller than expected

First, we analyzed an Xbox 360 that we purchased in late 2005 to evaluate the console's standard power consumption and heat radiation when playing a title that required a lot of computing power for 3D graphics.

We measured the temperature of exhaust from the operating Xbox 360.

Power was about 170 W when playing a game.

The Xbox 360's power was about 170 W when the DVD equipment was running. The temperature of emitted air was about 45°C. A temperature gap with the room temperature (23°C) was 22°C.

"When designing consumer products, it is common to seek a temperature gap of around 10°C between exhaust and room temperatures," the thermal design expert said. "The 22°C is quite a large gap, in the first place."

The cooler fan's maximum wind speed was 1.1 m/s, only 1/2 to 1/3 compared with general desktop PCs. It may be partly because the fan rotation was reduced to lower noise. According to an expert's analysis, "The amount of switched air is slightly in short considering the chassis' size (309 x 258 x 83 mm3)."

Then we forced the Xbox 360's chassis open and exposed its main board.

"The heat sink on the graphics LSI is so small, I wonder if it can really cool down the board," our expert said.

Located at front end is the graphics LSI heat sink. At the back is the microprocessor heat sink equipped with a heat pipe.

Microsoft apparently had no choice but to downsize the graphics LSI heat sink in order to locate a DVD drive above it. The DVD drive's bottom surface covers the top of the heat sink and forms an air channel.

"In most PCs, a solid duct covers the top of the heat sink in order to secure an air channel," the expert said.

In the Xbox 360, however, the duct was cut off before the heat sink and the DVD drive, and, instead, chassis took up the heat sink's upper area probably due to limited space inside the chassis.

The temperature of the LSI goes over 100°C

To confirm the cooler system's performance, we measured the temperature of heat sinks. Attaching ends of a thermocouple to each heat sink for the microprocessor and graphics LSI, we closed the chassis and then switched on the Xbox 360.

"Wow, the temperature is rising fast..."

We attached ends of a thermometer to the two heat sinks.

Measuring temperature with the chassis closed

In only five minutes since we started playing the game, the temperature of the heat sink on the graphics LSI rose to 70°C. The thermal gradient was about 10°C/min.

In 15 minutes, the microprocessor heat sink temperature stabilized at 58°C, but the heat sink on the graphics LSI rose to 80°C, 57°C above the room temperature.

Assuming room temperature of 35°C in mid-summer, the gap is estimated to reach more than 90°C. In that case, the temperature of chips in the graphics LSI could exceed 100°C.

We measured the temperature in good cooling environments, removing dust and obstacles from the vent hole, for example. If the cooling performance lowers with the vent hole choked up or the duct moved over, the LSI's temperature could get even higher.

If the malfunction stemmed from insufficient heat radiation, the graphics LSI and components around it are highly likely to be the failure parts.

Microsoft did not change the thermal design in the repair

Finally, we opened the chassis of the Xbox 360 repaired in May 2007 and compared it with the other Xbox 360 we purchased in late 2005.

"Huh? The heat sinks and fans are completely identical, aren't they?"

To our surprise, the composition of the repaired Xbox 360 looked completely the same as that of the Xbox 360 purchased in late 2005. It turned out that Microsoft provided repair without changing the Xbox 360's thermo design at least until May 2007.