I have quite a number of VAV boxes and all have speed control on them. All are 277volt and have model ETFC277-8 speed control boards. the problem is that the resistor and part Q2 keeps burning out. I am trying to find out what the specs are for this part Q2, it looks like a small diode but no polarity is marked. i am thinking that it may just be an overload protection. i would like to get these boards repaired if possible. Any help appreciated, thanks