My Book power supply
My external USB disk stopped working a while ago. It turned out the culprit was the little 12 V power brick which appeared completely dead.
I took it apart and poked around it with the multimeter. It's a pretty simple 30 W switcher using a PWM chip in a tiny 6-lead SMD package (marked 63813 - I'm guessing it's a 6-lead version of the 3813). Nothing was obviously bad, so the next suspect was the power MOSFET. I desoldered it and did a couple of tests and it worked as expected. I soldered it back and, surprise, everything worked perfectly.
Interesting. I recently see a lot of power supplies that fail because of bad soldered joints. Is the use of RoHS materials (i.e. lead-less solders) to blame? On a high-powered ones this usually have spectacular effects because the heating and arcing will make a big black spot on the board. But in this case the pins of the MOSFET looked perfectly OK.
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