Try reseating the +48 Volt main PS.  Next, check J2-5 on the +48 Volt PS.  If there is no control Voltage there, remove the main AC input to the STX Transmitter and measure J2-5 to ground.  If J2-5 is zero Ohms, check C1 on PS motherboard for a short. Also, check for a pinched control wire #29 from PS mother board J2-5 to controller card.