I have a mystery part labeled NEC AC100.  It's from the low voltage
supply of an NEC Multisync I monitor.  It's a three lead part in a
square package like a volate regulator or power transistor.  The board
is labeled CR691 where the part goes.  (Possibly an SCR?)  The pin
labeled G on the board goes to a zener diode (reference voltage?); the
pin labeled T1 goes to the negative lead of a capacitor in the power
supply, and the pin labeled T2 goes to the negative side of the bridge
rectifier in the supply.

    If anyone can tell me what this is, or better yet, where I can buy
one just like it, please email me at ck3i@andrew.cmu.edu.  I've called
NEC's "monitor repair number" and not only do they not know what the
part is, but they don't think that they can find one to sell to me... 
It makes no sense to me...