Nothing happens at power-on: no display and no CPU LED activity.

CPU board completely dead

Cause: Often the address and data lines are stuck or floating from a bad chip, a solder bridge or cold joints, or the board has no +5 V or ground.

Checks

• Confirm +5 V and ground at the board.
• Look for solder shorts or cold joints under chips and sockets.
• Check that the latches show activity (about 4 V pulses) and that the 8 MHz and 32 kHz clocks run.

Fix

• Isolate the fault by substituting known good chips for U4, U6 and U9, changing only one each time.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Dead CPU: isolate it from the other boards
• Dead CPU: check the reset and IRQ lines
• Reseating the U9 ASIC on a dead CPU board
• Dead CPU: the order to replace chips
• Signals a dead CPU board should show
• Dead CPU: checking address and data lines
• Outhole, shooter diverter and gumball motor all dead: CPU board chip at U4
• Dead CPU: no clock signal at the 6809

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part One, Clay Harrell (pinrepair.com)