The E to B voltage of T4 (0.3V) seems to not be enough to turn it on. Maybe checking directly with probes at E and B will give a more accurate reading than checking voltage to ground.
The voltage to turn it on should be developed across R5. That is created because of current through T1. What are E,B,C voltages for T1 and T2 ?
The voltage to turn it on should be developed across R5. That is created because of current through T1. What are E,B,C voltages for T1 and T2 ?