The player 3 and 4 score displays are out, and the player 1 display is faint and patchy.

Player 3 and 4 displays dark: worn out display glass

Cause: The gas-discharge display glasses had outgassed and worn out. All the displays share one board, so a supply fault would not take out just two of them.

Checks

• Reseat or replace the display ribbon cables first, since a bad cable can also kill displays.
• Check the display high voltage and 5 V at the display board.
• Look at the glasses: dim, patchy or dark segments across a glass point to worn-out glass.

Fix

• Replace the bad glasses, or fit an LED replacement display board.

Gas-discharge displays run on about 100 V DC or more. Power off before handling the display board.

Systems

• Williams System 11A

Games

• Big Guns

Related tips

• Score display layouts across System 11
• Score displays weak, dim or dead with fuses good
• Telling a shorted UDN chip from a shorted display glass
• Displays dead after the CPU board was removed
• Score display digits dead or dim
• Check every segment with the display test
• Display completely dark with high voltage present
• System 11 alphanumeric displays

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