You can find out about Triacs here...
http://en.wikipedia.org/wiki/TRIAC
It's an AC switch useful for controlling electric motors - they get turned on and off at relatively high speed to limit the power and consequently the speed of the motor being controlled. If it's gone short circuit then there's no control and the motor will run at full speed.
You find the numbers on the triac, buy a replacement and use a soldering iron to exchange the old for the new (three legs). It will probably be on the main control board and fixed to a metal heat sink (probably painted black) with a screw and have a white, heat-conducting paste between the two. You will need new paste too.
It may be however that the Triac has not failed and that the control circuit is making it stay permanently open. In this case you may need a new control board.
The control board will probably be situated just below the machine's top cover.
Good luck...
Peccavi, May 2009
