I took a look at the schematic just an hour ago (did not know it was published), so maybe my suggestions will not be so effective.
As far as I understood the LED near the front panel lights up, it means (at least) that the basic voltage from the external PS is here.
I guess that you have checked the voltage across C5R26? It's better to check if the U1 is oscillating, but I can't see the way to do it without o'scope (if my countings are right the oscillating frequency is above the hearing capabilities - 48kHz). Then let's begin with visual checking: check if the U1, Q1, D1 have been soldered correctly (orientation and cold joints). Then check the D1 and the voltages on the Q1 leads. If you have a spare IRF740 you can try to change it.