It could be a number of things...
It could be the fuses or fuse block... under $3 repair.
It could be a bad monitor ... $5 to $70 repair.
It could be a bad isolation transformer... $15 repair.
It could be a bad linear AC transformer.... $20 to $40 repair (Pac-man's can use Galaxian's ones... you need 120VAC in, and +7VAC and +14VAC output)
It could be a bad diode or capacitor or trasnistor on the pacman board to convert AC to DC.... $1 to $20 repair.
Need more info to tell for sure.
And no, dont mame it. It *IS* the most common cabinet out there, but if the artwork is in good shape, that's worth a lot. I'd HAPPILY trade you a pac-man that had formica on the sides and now all the artwork is destroyed (they scuffed it up to make the cement stick)....