Allen & Heath XONE 464 Power Supply Board

I am having difficulty in repairing an Allen & Heath Xone:464. It had a blown fuse and 4N80 MOSFET. I replaced them along with a few diodes and the UC3842 chip as well as a fried 150-Ohm@ 1-Watt resistor. It is still not working and I'm having difficulty as I do not know if is due to the low oscillator frequency of 380Hz,, since the UC3842 datasheet implies that it is far too low for spec. The output of the UC3842 (which I replaced twice) is 500mV, which I believe is far to low to turn on the 4N80 MOSFET that requires around 5Volts!