Power Supply Failure

[Bob Ayers]

A friend brought his computer to me last night to look at. The power supply had died, but what I found was amazing. The NFET "switcher" for the standby power supplies shorted out, and it blew the drain lead completely off the NFET. And what made it even more amazing, the fuse didn't blow! I'm
hypothesizing that all the energy for this event came from the decoupling capacitors, and the Di/Dt from the inductance of the transformer primary. The main bridge diodes were ok, as well as the rectifier diodes off the transformer secondaries.

Here are some photos of the carnage:

Red arrow is where the NFET drain lead used to be:

 

[Syko]

Nice picture quality!

 

[Bob Ayers]

Thanks!

Just an update on that poor little power supply. I was having trouble explaining how a single current transient that took the lead off the FET
would burn the PCB like it was. After sending out these photos, I found
that the fan was frozen, so it's hard to say how long, and how hot the
components have run, before the FET failure.