After new ribbon cables were fitted with one connector shifted one row of pins over, a fuse blew at power-on. With the cable corrected and fuse replaced the game still won't boot: the CPU diagnostic LED stops flashing and the game stalls a few seconds into boot with an audio pop.

Won't boot after a ribbon cable was fitted one row off: unplug boards to find the damage

Cause: Plugging the ribbon off by a row forced signals on the shared CPU ribbon to ground or to the wrong voltage and damaged parts on a board on that ribbon; here the sound board was holding the system down.

Checks

• Check every fuse again with a meter.
• Check all supply voltages on the power driver board with the logic ribbons unplugged.
• Unplug the ribbons from the CPU and see if it boots, then plug the boards on that ribbon (Fliptronics, sound, display) back one at a time; the one that stops the boot is damaged.

Fix

• Repair or replace the damaged board (on the CPU side the bus buffer chip is a common casualty). Here the game booted with the sound board unplugged, and bad transistors were found on that board.

Systems

• WPC DCS

Games

• World Cup Soccer

Related tips

• CPU diagnostic LED blinks a code instead of flashing steadily
• Reading the CPU board LEDs at power-on
• WPC CPU board LEDs at power-on
• Coin door Begin Test button does nothing: acid-broken trace on the CPU board
• WPC CPU board LED meanings
• Resets remain after rectifiers, caps and connectors are done
• Factory settings restored at every power-up after new batteries: do a factory reset
• What a WPC game reset is

Source: Pinball Repair help group!! (Facebook group)