I apologize for dodging your question. Q203 looks like hell in the picture. I tested each leg of Q203 vs other parallel components/FETs with the continuity function on the DMM. The copper was pulled off the top of the board by the previous owner and wanted to ensure the soldering was good. I may have misused the term 'continuity'.
Center legs of the rectifiers:
D62 53.xx - 54.xx volts
D63 53.xx - 54.xx volts
I have no clue as to what the correct rail voltage is.
Things may have taken a turn for the worse. I hooked it up in my vehicle to a set of 4ohm woofers. My deck was set at zero volume. Hit the power, lights pulsed in the cabin at the same rhythm of the faint clicking in the amp, two 40A fuses on the amp blew. Took it back to the bench, plugged in two 15A fuses. Applied power, blew the 15A fuse inline with my power source. Jumpered the fuse block, then blew both 15A on the amp.
The amp was drawing about 1A idle when I first got it.
All I've got to limit current for further testing is a 10watt 10ohm resistor.
Check all of the components clamped to the heatsink to see if any center terminal reads 0 ohms to the heatsink. Make sure that you have one probe on a bare place on the heatsink. A screw hole where the screw has cut through the anodizing is generally a good place for the probe. The components need to be clamped as they normally are.
Dangit. I can put it all back together and follow your instructions.
I already tore it apart, put a 10ohm resistor in series with +B. Read 1.1A draw and no power to led. Then proceeded to pull Q203 (REP40N10). No change in current draw. Next I pulled Q42 (IRF3205). The current dropped enough to where I felt I could power the amp without the 10ohm resistor. The led is now powered on, and the relay clicked. I still hear a faint-rhythmic clicking somewhere.
The 20 pin IC is an HIP4080. If the amp functions without the shorted IC, the 4080 is likely OK.
Doing as suggested in #6 will cause no harm unless something is wrong with one of the controls or the circuit they're connected to. It still has to be done.
Many times, the only reason that an amp is not producing audio is due to a dirty switch contact or dirty/damaged potentiometer. Before doing any work on an amp that's powering up, checking the pots and switches will reveal that the problem is simple and requires no repair of the amp.
The gate resistors don't generally need to be replaced (unless out of tolerance) for amps that use the 4080.