Dead CPU: the order to replace chips

Steps

• Replace U1 and U2 (74LS244, address lines) and U3 (74LS245, data lines) first.
• Next U5 (74LS14, clock), unless the clock signal already checks good.
• Then U7 (74LS244) and U12 (74LS240) on the data lines.
• Check R95 and R99 are 1 meg ohm.
• Finally replace U10 (MC34064 reset).

Systems

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

Related tips

• A dedicated (direct) switch does not work
• Dead CPU: isolate it from the other boards
• One switch column dead: parts to check in order
• Fixing a dead switch column on the CPU board
• Reseating the U9 ASIC on a dead CPU board
• Switch column (drive) circuit on the CPU board
• System 11 switch matrix: connectors and chips
• Signals a dead CPU board should show

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