My wife noticed her computer seemed to cut out when she happened to bump the power cord. There is a blue LED on the power converter brick that indicates it is working. While she was showing me how moving the power cord often caused the computer to shut down I happened to notice the blue LED went out at the same time. Wiggling the strain relief on the load side of the power converter frequently caused the blue LED to light again.
Screwdriver for prying
Third hand to hold wires for soldering
Step 1: Crack the Case
Step 2: The Case Opened
The connector that plugs into the computer is supposed to be center point positive (+), according to the label on the side of the converter brick. Do some checking with an electrical meter to be certain the polarity is not changed during reconnecting the cable.
Step 3: Soldered and Insulated
Step 4: Close It Up and Test
I confess I accidentally reversed the polarity when I soldered the cable to black and white wires coming from the circuit board. It was easier to do than one would think because the internal construction of the cable was counter-intuitive. But, now the power converter that seemed to be defunct works. Whereas my wife's notebook computer worked fine when on battery power only, it now works fine on AC power without any spontaneous shut downs.
What was the problem? A simple break in a wire inside the strain relief should not have caused a spontaneous shut down. The computer should simply have drawn from its battery. But, a short in the strain relief seems more likely to cause both the power supply and the computer to shut down. I say that because shorting a gray wire to ground on an ATX power supply for a desktop computer causes an immediate shut down by dropping a critical CPU voltage below a minimum standard. (Deliberately shorting that gray wire momentarily can be used to make a reset button on a computer that has no reset button.)
The most surprising thing about this solution to a spontaneous shut down problem is that the cause was not something inside the computer, but something in the power supply. Spontaneous shut down issues are usually due to an overheated CPU, which can be caused by dust plugging the cooling fins, or to a faulty RAM memory stick. An exception for a desktop computer is that a faulty power supply often causes shut down problems, but a desktop does not have a battery from which to draw operating power like a notebook does.