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 Post subject: Xbox360 Design issues
PostPosted: Sun Sep 28, 2008 1:06 am 
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Owners of Xbox 360 consles are frequently experiencing the RRoD (Red Ring of Death, after just a few weeks or months playing. Further investigation has revealed it is due to heat buildup in the console, and the way the processor and graphics chip is cooled, and the way the heatsink and cooling mechanism is designed. The 360 uses a heatsink bracket known as the X-Clamp.

The X-Clamps clamp the heatsinks to the processors. There are 2 processors. The GPU (Graphics Processing Unit), and the CPU (Central Processing Unit)

The processors get quite hot during use and emit a lot of heat..they can get as hot as 50 - 60 Deg C at idle, and higher than that under load, depending on the operating environment.

All computer processors are the same. All computer processors emit a lot of heat...but most run a lot cooler because computers have better cooling than the 360. The 360 has two rear mounted 80mm fans, to pull the heat from the CPU and the GPU....a PC usually has separate units for both. This is why the 360 suffers.

The processors would pretty much instantly overheat if you didn't have heatsinks, the thermal cutoff for the chips is around 90 degrees C. Heatsinks are basically big lumps of metal with fins that spread the heat out and dissipate it into the air. Since air is not a good conductor of heat, that is why heatsinks always have multiple fins...the more surface area, the more heat dissipation.

Below is what the heatsinks of the 360 look like:

Image

As you can see, they both have hexagonal mounting posts on the bottom of them, there are 4 per heatsink. They insert through holes on the motherboard and protrude through the rear of the board, the X-Clamps attach to those mountings and clamp the heatsinks firmly onto the processors.

If you just placed the heatsink on top of a processor, the convection process is inefficient. The cooling method uses convection, very similar to a radiator, and there needs to be a firm connection. There also needs to be thermal transfer paste between the processor and heatsink, to aid the convection process.

Below is a picture of the X-Clamps. Here you can see where they mount to the heatsink:

Image[/img]

The CPU and GPU on the xbox 360 are soldered to the motherboard via what is known as BGA (Ball Grid Array) soldering. There are several different soldering methods, i detail them below:

PGA (Pin Grid Array) - This is where the processors pins are in a grid, and protrude through to the other side of a Printed Circuit Board (PCB), and are finely soldered. Although the soldering looks fine and delicate, it actually is quite sturdy, and can take quite a bit of force to break.

Here's a picture of a PGA package chip, and it's socket:

Image

BGA (Ball Grid Array) - BGA is derived from Pin Grid Array (PGA), which is a package with one face covered (or partly covered) with pins in a grid pattern. These pins are used to conduct electrical signals from the integrated circuit to the printed circuit board (PCB) it is soldered on.

In a BGA arrangement, the pins are replaced by balls of solder stuck to the bottom of the package. They are very alike to micro ball bearings. The device is placed on a PCB that carries copper pads in a pattern that matches the solder balls. The assembly is then heated, either in a reflow oven or by an infrared heater, causing the solder balls to melt. Surface tension causes the molten solder to hold the package in alignment with the circuit board, at the correct separation distance, while the solder cools and solidifies.

Below is a picture of the underside of a BGA chip, with its solder balls:

Image

LGA - Land Grid Array - The Land Grid Array (LGA) is a type of surface-mount packaging used for integrated circuits (IC's). It can be electrically connected to a PCB by the use of a socket or by soldering directly to the PCB. LGA is used as an interface for microprocessors of the Intel Pentium 4, Intel Xeon, Intel Core 2 and AMD Opteron families. Unlike the Pin Grid Array (PGA) interfaces found on most AMD and older Intel processors, there are no pins on the chip, in place of the pins are pads of bare gold-plated copper that touch pins on the motherboard.

Below is a picture of the underside of an LGA chip, and next to it, an LGA 775 socket:

ImageImage

How the X-Clamp Works

The X-Clamps work by holding the heatsinks down onto the processors with even force on each corner. If the force on each corner was not equal, this would result in processor damage, or cooling issues. They pull the heatsink mountings down onto the motherboard, pulling the motherboard downwards. But they also push up on the motherboard close to the middle of the processor resulting in warping of the motherboard. The constant heating and cooling of the whole assembly warps the motherboard, causing the solder balls under the chips to break, causing intermittent contact, and the dreaded RRoD, below:

Image

When the Red Ring appears, it is only segments 1 3 & 4, lit up, flashing. Any other Red Ring sequence means something else. See our Xbox360 Error Codes & Solutions Thread for more help.

Tutorials for fixing to be added soon.

_________________
Regards,

James (Kitamura Computers Director)

james at kitamuracomputers dot com


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