Driver circuit not controllable, heating up
Your voltages don't make sense if the circuit is as shown. However they do if the Collector and Emitter leads of Q1 were swapped around. The transistor would still work (with greatly reduced gain) but the 4.7k Base-Emitter resistor would cause it to be partially turned on even when the opto-coupler was off.

Check the traces going to the PDTA143ET. Are they connected to the correct pins?