Can anyone identify (what I believe is) a surface mount transistor labelled as "43" ?
It looks like a SOT-23 package. Possibly PNP looking at the circuit.
This appears to be switching the gate voltage on a triac (switching 240V mains). The transistor itself is driven straight from a microcontroller with no limiting resistor ???
My searches match only a Schottky diode barrier - which seems unlikely.
Thanks,
Mark.