I have seen all flashers out on a game and it turned out that they were all simply burned out. Always start simple. Replace one bulb and test. Since the boards led is also out, the board is probably the problem. But I have also seen those indicator LEDs die. So make no assumptions. These would be your steps:

1) dmm the fuses - all of them.
2) replace at least one flasher bulb
3) if fuses are ok and bulbs are ok start checking power at the board. The circuits here are simple. Input power to fuse, to bridge, to cap, out. If you don't have 20vdc at your flashers with the coin door closed, check for voltage at the flasher connector. If no 20vdc there, test / replace the bridge rectifier and associated cap. Look at traces of these components. Possibly dmm the traces.

Hopefully you get the idea from there.

Well to trace power you need the board installed and running.