Random vertical lines on the display that get worse over time, until all four flippers energise at power-on (seen on Twilight Zone).

Random display lines and all flippers energising at power-on

Cause: The single ribbon cable carrying address and data lines from the CPU board to the Fliptronics, sound and display controller boards is fitted a pin off, torn at a connector or dirty. Missing 12 V at the display controller can also cause it.

Checks

• Check the ribbon is on each header correctly and not torn.
• Measure 12 V at the display controller.

Fix

• Reseat or replace the ribbon cable.
• Repair the 12 V supply if it is missing.

Systems

• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)

Games

• Twilight Zone

Related tips

• Outgassed displays and the 5 V supply
• Dot matrix display goes blurry within minutes
• DMD dead though display and controller work in other games: CPU board fault
• Random vertical or diagonal lines: 12 V missing at the display
• Missing rows or columns on a pin-style display
• Test report lists switches the game doesn't have
• Twilight Zone ninth switch column (clock switches)
• +62 V reads over 70 V

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