My Pi has been randomly turning off with a Mean Time Between Failures of a minute. People experiencing this problem also said that putting their Pi on an ice pack allowed their Pi to operate indefinitely. I tried this and it allowed my Pi to far surpass its MTBF.
Others said that Polyfuse F3 could be to blame. To test this I put the ice pack on just the corner where F3 resides and the Pi operated without issue, and to make absolutely sure an over heating polyfuse was the issue I blasted the rest of the Pi with an electric heater.
Convinced that the fuse was probably blowing far below the current it's rated at, I shorted it out. But the Pi shutdown shortly after being turned on in this configuration.
This suggests that the polyfuse is not the culprit but rather it is another component in the area (D17, R51, RG2, C2, C3, C6 or S1). I believe that the micro USB connector, which delivers power, is the next likely culprit.
How can I bypass the micro USB connector and deliver power directly to the Pi? I'm tempted to put a ground wire at T2 and the 5v rail at T1, but I'm worried that they're not directly attached to the gnd and power rail on the Pi.