compaq SLT PSU dead.

Compaq SLT PSU dead. Power DC plug is DEATACHABLE from power brick, model number: 2687. Other SLT PSU bricks aren't deatachable. No signs of power and fuse not blown. Uses compaq's relabeled common UC3842 pinout PWM ic, yes I traced enough from the UC3842 datasheet. Single chopper tranny is MOSFET (BUK456-800A by philips). R512 and R500 are now ashes. I need the resistor values on these. What good subs for this MOSFET? And any gotchas? I have looked up on this specs on this transistor but I'm not so sure and *very* diffcult to buy that correct part so I need to sub this transistor out from bunch of choices that has 1-MOSFET PSUs with different types of 8pin UCxxxx PWM on it. Everything else are fine. Cheers. Trying to get SLT 286 going because other bunch of SLT 286 and SLT 386s/20 was given away with own working bricks. Those working bricks was not correct model like this kind I have in pieces and this is remaining SLT 286 I want to keep. Wizard