On Tue, 15 May 2007 19:36:48 +0100, Clint Sharp
wrote:

In message , John Larkin
writes


[ A UUEncoded file (ExFets.jpg) was included here. ]

Brings back memories. Wish I'd got pics from when I used to repair PSUs.
One PSU (DEskpro 386N IIRC) used two IRFP450 FETs mounted on some nice
3/16" (approx) thick aluminium heatsinks. These devices have a failure
mode that shoots molten metal out of the back of the FET package through
the copper back and clean through the thermal pad and heatsink as well,
welding itself to the heatsink in the process. We used to be *very*
careful when powering these up after a repair.

Clint Sharp

I've seen TO-3's with holes burned through the metal can top. Wish I'd
taken pics.

John