The displays light but show scrambled characters.

Displays show gibberish

Cause: Often a weak backup battery, common on newer games with a lithium cell.

Checks

• Measure the battery voltage (a lithium coin cell should be a little over 3 V).

Fix

• Replace the battery and see if the display returns to normal.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7
• Williams System 9
• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C
• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95
• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200
• Bally 6803
• Gottlieb System 1
• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B
• Gottlieb System 3
• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b
• Capcom

Related tips

• F-14 Tomcat: left credit-display character scrambled
• Displays never show the digit 1
• Displays have high voltage but stay blank
• Wrong-looking digits or bad "1"s
• CPU LEDs flash and go out but the score displays stay dark
• Display shows "Command" numbers instead of animations
• Display fault: board or display?
• Blank display, garbage or diagonal lines: reseat ribbon cables

Source: Pinball Machine Care & Maintenance, Bernard B. Kamoroff (Bell Springs Pinball Alley)