Mackie srm450 power light out

If its the blue front light you are talking about it is a fiddly but simple fix.
1 phone mackie and order an l.e.d. about £2
2 when it arrives take out the woofer and carefully lay to the side.
3 use a very small philips screwdriver, a tiny bit of blue tack, a mirror and a torch to remove the screw holding the small circuit board with the l.e.d.in place (the blue tack is to put on the tip of the screwdriver to hold the screw and the mirror and torch is so that you can see it)
4 remove the small circuit board and un-solder the l.e.d from it take note of the orientation of the contacts as they only work one way round) and resolder the new one in place.
5 check that it works and re-fit the board and screw ( this can take 2 seconds or 2 hours depending on how lucky you are and how sticky the blue tack is.
6 re-fit the woofer and grill.

the other way is to split the cabinet using the screws on the back and then the repair is obvious from number 4-5