The mainboard is Samsung DE92-03761B. Smoke filled the house but the actual damage was a little difficult to find, turned out to be a cheapo Chinese high voltage relay, Golden GK-D-1C-12D, SPDT 12V. I'm going to file a complaint with the CPSC. Samsung gave me a ticket number but never called or confirmed via email - service is really poor. The problem with this particular failure is in the design; when the relay fails the default state causes current to flow unchecked to the element rather than disconnecting it. This leads to a thermal runaway of the element, causing he heat to increase out of control. Proper circuit design should never allow this to happen.