You may have figured the problem out already. The voltages around Q4 are off, especially at the collector. The collector should have about -3 volts there and not the -33 volts that you have.
That would lead me to believe that the transistor is breaking down when hit with the full voltage of the circuit or that C7 is shorted. As you don't have the correct replacement for Q4, remove C7 and see what happens.
As for the CR4 question, that diode is part of the limiter circuit. That -25 volts is being blocked by the diode and with a negative voltage being applied to Q7 base and emitter, I would expect the transistor to be turned fully off, preventing any voltage from showing up at the collector.
The power amp does not need the limiter circuit there to operate, so you could remove both CR4 and CR5 from the circuit for testing.