Reviving a dead sub amplifier

Hello,

my Boston MCS-95 no longer functions, standby LED is off, no sound. The fuse is fine, and even the post rectifier stage ~350V at the half bridge driver appears to be good. Found an old post about the 18V zener being blown, but the replacement didn't fix mine.

So I could scrap the whole thing and buy a new one, but what fun is that?

I have the full schematic, background in EE (microwaves mostly) and plenty of test tools.

Any recommendations of where to start to understand these class D amplifiers? a

Thanks in advance