Rule of thumb on the Bally / Williams machines - change all the Bridge rectifiers and capacitors. Caps are usually rated to 10 years, so they are overdue anyway ! I covered the process on my Addams Family thread, Page 4 - http://aussiepinball.com/index.php?topic=2969.45

The parts are available from RTBB. You can also replace just the corresponding +5VDC cap ad BR. You could also replace C4 It's a 100uf, 10V cap (from memory).

As Beaky mentioned, check the diodes on the flipper coils as this would be the easiest and cheapest fix.