Bench-check the System 11 CPU switch matrix circuit

Steps

• Enter the switch levels test and unplug 1J8 (columns) and 1J10 (rows). No switch should read closed; if one does, the board is faulty.
• Rows: hold a lead on 1J8 pin 1 and touch 1J10 pins 9 down to 1. Expect switches 1 to 8; pin 4 of 1J10 is a key and gives nothing.
• Columns: hold a lead on 1J10 pin 9 and touch 1J8 pins 1 to 9. Expect switch 1 then every eighth number up to 57; pin 6 of 1J8 is a key.
• Any missing number means the CPU/driver board is faulty. If column 8 is unused on the game, its missing reading is normal.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• System 11 lamp matrix
• System 11 CPU/driver board transistor locations
• System 11 backbox boards and supplies
• System 11 coil outputs
• How the System 11 A/C bank select works
• How System 11 special solenoids work
• Which System 11 CPU boards fit which games
• Running the CPU board on the bench

Source: Pinball Machines: How They Work & Troubleshooting, Norbert Snicer