QUOTE(Elemino @ Mar 1 2007, 11:56 PM)
I'm not discounting your theory or anything, just trying to help come up with the right answer. So please don't take this the wrong way.
If this issue was caused by the board flexing, how come it does not affect PCs? These days, heat sinks are getting heavier and chunkier all the time. Some of the large ones made by Cooler Master and such companies are huge. They hold on to a processor and board and dangle that weight horizontally. They've gotten so large that some need bracing that goes on the under side of the board to keep the heatsink from ripping the socket off the board. To add to that, in my PC I'm using Cooler Master's Aqua Gate Mini (Seen below) and the pump/heatsink that sits on the processor has a bracing that goes underneither to CPU to litteraly sandwhich, hold and apply force to the CPU to make sure it has good contact as well as a secure mount.
I'm all for discussing the whys and why nots to try and get the proper answer.
There are multiple reasons you don't get the problem on PCs.
1) The PC mainboard is properly secured to the baseplate via pegs/standoffs at multiple points across the board. This keeps the board nice and flat and prevents warping. On the 360 the board is only secured around the edges leaving it lots of room to warp and flex.
2) Most of the PC heatsink clamping methods I have seen put the clamping pressure *outside* the perimeter of the CPU, i.e. it attaches to the board or baseplate at 4 anchor points which surround the chip(which is what should be done on the 360) i.e. the clamp pressure is not focussed on the bottom side of the board under the centre of the CPU.
If the CPU/GPU was just a flat plate that sat directly on the board perhaps you wouldn't get as much of a problem, but the CPU/GPU sit above the board on top of the solder balls. So there is an air gap and therefore no equivalent downwards pressure from the top.
So the upwards pressure point under the centre of the CPU/GPU does not have the CPU/GPU sitting hard against the top of the board so the board wants to flex upwards at the centre point (towards the chips) causing the rest of the board to want to flex downwards (away from the chips).
You can simulate the effect quite easily and see it happen.
Clamping the chip down properly (like on a PC) and securing the boards properly (like on a PC) makes the problem go away.
Last night I put the original clamps back on and had the ring of death within 20 minutes, put my PC style clamps back on and played for the rest of the night without incident. I fired it up again today and it is still running just fine.
So it is looking like the culprit, but really I will only know if my 360 is still running in 6 months time I guess.