You should start by reseating your connectors to the DMD and checking voltages. This should get you started. Just copied from the net.
Voltages Needed for the DMD Controller Board.
Since all the dot matrix displays essentially have their own computer on the controller board to control the score display, a supply of good +5 volts is needed for the controller. If a display is not working, first check the controller board for +5 volts. Often the connector carrying +5 volts can gain resistance, which will lower the +5 volts. This can be enough to make the DMD not work (this problem happens most with the super-sized 192x64 DMD).
On the super-size 192x64 DMD, the input voltages are low (+5 volts and +24 volts coming into the display). Sega did this because the 192x64 DMD has it's own power supply on the dot matrix controller board itself (the highLer voltages are not supplied by the main power supply). This is unlike the other two smaller dot matrix
Medium 128x32 DMD, connector P1:
P1 pin 1: -110 volts
P1 pin 2: -98 volts
P1 pin 3: KEY
P1 pin 4: Ground
P1 pin 5: Ground
P1 pin 6: +5 volts
P1 pin 7: +12 volts (only used on Babcock displays)
P1 pin 8: +68 volts