Every game tilts as soon as it starts, the trough kicker fires on its own at power-on, and switch test shows the wrong numbers for several switches.

Instant tilt and scrambled switch test: burnt resistor networks on the CPU

Cause: A shorted tilt switch had burnt the resistor networks SR10 and SR11 on the CPU board that feed the switch matrix.

Checks

• Unplug the switch matrix connectors from the CPU and jumper rows to columns; wrong or duplicated switch numbers point to the board.
• Look for a tilt switch or wire that is shorted to something.

Fix

• Replace the damaged resistor networks and fix the short that caused it.

Systems

• Williams System 11

Games

• High Speed

Related tips

• Every switch shows active, even with the switch plugs removed: failed PIA at U38
• A whole switch row or column is dead
• Knocker fires several times at power-on with a switch number shown
• Random switch closures, random tilts or slam from bad resistor networks
• Switch matrix resistor networks and their values
• Bussed versus isolated resistor networks on the CPU board
• Displays show only 0s and Xs at power-on
• Testing a resistor network with a meter

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