The C1 transistor is a JFET and will read approximately 10 ohms out of the circuit between drain and source. Look up the datasheet. The two legs that you refer to as base and emitter are drain and source. The top leg is the gate.
J5 is the marking for the part number. That converts to MMSZ5250B. Contact MTX if you want confirmation.
Until you get the regulators working properly, I'd suggest pulling the two 3120s and soldering a jumper connecting pins 5, 6 and 7 on each 3120. This will prevent damage to the opto-couplers and the jumpers will keep the outputs from switching on.