Check your voltages on the display connector. In DC volts test (set to 200v if manual select meter) attach black lead to ground strap and red lead from left to right on the display connector. DO NOT jump pins, be very careful and touch them one at a time with your red lead. Report what you find, sounds like your cathode or anode voltage is too high. What brand of power supply did you buy?

Actually I've learned there is a way to check fuses without removing them. Just test for voltage across both terminals. If it's 0 you're ok. If there is voltage then the fuse is open. In the case of an open fuse, there is a voltage difference across the 2 terminals and that will get picked up by the meter like any other source of power. If it's good the voltage across the 2 terminals is the same, which means no difference in potential and a reading of 0 on the meter.

Oh you're using a Rottendog board? I would avoid those as they have a flawed high voltage design. The regulators are being driven out of spec and can fail prematurely in a nasty fashion. But that wouldn't cause the ripple you are seeing in the cathode supply. The presence of ripple would cause rolling bars on the DMD. Try again with your original power supply. If that solves it I would send the defective Rottendog back and get an X-Pin board from xpinpinball.com. Buy it from K's Arcade on the distributors page. A little more expensive but I've heard they are designed better than the original boards and other aftermarket brands.