+1 to MartyJ suggestions. Also worth checking each coil or coil lugs are not shorting out on anything nearby. If the coil wrapper is ripped, have a look that nothing is rubbing against it. Also pull the shooter and kickout assemblies apart and check sleeve and inside the coil. Its a real long shot but I have seen coil which had worn through to the windings on the inside.
You could also try running the game without the display connected as it might be loading down the 5v. I have seen a few of these DMDs faulty.
Could also try putting game in switch test and then banging gently on the playfield and see if any switches trigger.
PPB boards also can have dry joints on the headers and relay but this tends to cause other problems.
