Any chance the 85 deg OOR Thermal Switch J1 is stuck open, and has to be 'throttled' to close (normally closed). If open, it will be in protect, and the front end is turned off, since it's not turned on, so the constant current source on the front end isn't running.
I assume you've re-connected C25, C26 & C27. I see no reason NOT to have the Zobel network. On the 1001RB, those output caps across the output jacks are 4.7nF instead of the 10nF you have on this.
The Fan normally doesn't run until the heat sink gets above 45-50 deg C, then begins running, speed being temp-controlled. I forget air direction. If this is installed in the combo case, it seems there's no gap above the top cover, so if it were exhausting out the top, it would put back pressure on the fan.