Judging by the fact that those holes seem to be clean, I'm gonna guess they were never meant to be fitted, or for some other versions, like Mike says.
if you can't find any schematics, best way to approach this would be to just look at how the device seems to be built and measuring some sensible points for voltages, as a start (ie, verify that voltage regulators are outputing the right voltages, check the voltages accros capacitors).
Of course, always do a visual check, and see if there are no black/other odd color marks on the pcb and/or components.