Dead CPU: checking address and data lines

Steps

• Set the meter to continuity.
• Check A0 to A12 and D0 to D7 between the 6809 at U4, the game ROM (G11/U6) and the U8 RAM.
• Check A13 between the ROM and U4.
• Check A0 to A15 and D0 to D7 between U4 and the U9 ASIC.
• Repair any open line with wire-wrap wire. Flexing, scratches and earlier repairs commonly break these traces.

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
• Reseating the U9 ASIC on a dead CPU board
• Dead CPU: check the reset and IRQ lines
• Signals a dead CPU board should show
• Dead CPU: no clock signal at the 6809
• What is on the WPC CPU board
• CPU board completely dead
• Which System 11 CPU boards fit which games

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