Using salvage power supply, RM1-3490 HP Laserjet
To power up the board's 24v rail I shorted the NPN tranny and relay to ground.

As per rating on the output diodes, FCH30B10, and the switching FET, 2SK3568, the 24 rail can output a wooping 30A continuously.

Only question remain is the function of the opto next to the relay. The placement suggest it is sensing current on the primary side maybe?!
Pin 7 on the multiple wire plug is the collector of the opto...

To power on:

Plug with purple wires

Pin 8 to GND
Pin 6 to GND