When the power amp is correct DC output voltage (blu wire) on speaker jack must be 0V +/- few mV.
For blowing fuses at power amp "cause" are some of the faulty transistors, output Q1, 2, 3, 4 and, or driver Q704, 705, 708, 709.
For the beginning of the disconect collectors (red wire) of the output transistors from the power supply voltage, or remove them from the socket (if they are in the socket)
Measure DC voltage to output (blu wire) speaker jack. How much is it?
All measurements and repairs work without the connected speaker.