I know its a sill question but are the lamps ok?
have you tested with the diagnostics?

if you have and it still doesn't work Use your Multi Meter to test if you have +28V DC on the red wire to the flash lamps (connect the - wire from the MM to a ground braid)

If you have +24V DC on the red at the lamps then use a wire with an alligator clip on one or both ends and connect one end to the metal brackets that hold the PCB's or an earth braid and with the other end touch it on and then remove it (no more than a second ) to the metal tab on top of Q25. This will send a Ground pulse to the flash lamps. If the lamps flash when you do this then you have a fault on the board, it could be anything from a bad solder joint to a faulty transistor or I.C.

If it does not flash when you do this and the bulbs are ok and you have +28V dc on the red at the flash lamps then there is a problem in the wiring or a bad solder joint or a faulty plug where the wire for the flash lamp connects to the driver board.

WARNING: THERE ARE HIGH VOLTAGES IN THE MACHINE UNDER THE PLAYFIELD AND IN THE BACK BOX THAT CAN KILL, DO NOT ATTEMPT THE ABOVE TESTS UNLESS YOU ARE 100% SURE YOU KNOW WHERE THE HIGH VOLTAGES ARE. IF YOU ARE UNSURE GET SOME HELP FROM SOME ONE WHO KNOWS WHERE THEY ARE.

No offence is meant by the above warning, it is just there to make people aware of the dangers.