Two player displays lose their bottom row of segments, and the same resistors on the master display board burn out, even on a second master board.

Bottom segments missing and master display resistors burning: shorted display glass

Cause: One display glass has an internal short: corrosion between its two glass layers connects a digit to a segment, overloading and burning the segment resistors.

Checks

• Unplug one display at a time; when the faulty one is unplugged, the other display recovers.
• Look at the bottom-left pins of the suspect glass for signs of corrosion inside.

Fix

• Replace the faulty display glass (or have it repaired, or fit LED displays), then replace the burnt resistors on the master display board.

The displays run at high voltage. Turn the game off and let it sit before touching the display boards.

Systems

• Williams System 4

Games

• Stellar Wars

Related tips

• A segment missing on a score display
• Segment resistors keep burning
• Find a shorted display glass that blows F1
• Missing segments: check the UDN7180 with a probe
• Master display board versions
• Which UDN6184 drives which display
• All score displays dead
• UDN display driver chips

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