You could also try this procedure from the pinrepair website guides:
Dead CPU Step One: Remove the Ribbon Cables.
Before you do anything, turn the game off and remove all the ribbon cables from the CPU. This will issolate the CPU from the driver board, the dot matrix display board, the sound board, the fliptronic board (if your game has one), and any other connecting boards. The ribbon cables are at connectors J201, J202, J211, and J204 (on some games). While you're at it, you might as well remove the switch connectors at J205 to J209, and J212. The only connector still attached is J210 (the power connector).
After everything is removed but connector J210, turn the game on. If the CPU board boots correctly, the lower LED (+5 volts) should be on, the middle LED (diagnostics) should be blinking continually, and the top LED (blanking) should be off. If this is the case, turn the game off and replace the ribbon cables, one at a time, and turn the game back on.
Start with replacing the the driver board to CPU board ribbon cable first. Chances are good the CPU board will still boot with this cable connected. Next try the other ribbon cables. If connecting the other ribbon cables stops the CPU board from booting, chances are good the TTL chips across the top of the CPU board are the problem (U1,U2,U3 on all WPC revisions).
