The alien head opto (switch 42) always reads closed. Cleaning the optos, reflowing the board and checking the matrix wiring didn't help.

Alien head opto stuck on after cleaning: replace the opto pair

Cause: The opto emitter/receiver pair itself had failed.

Checks

• Unplug each side of the opto assembly and watch the board's indicator LED and switch test.
• Check the transistor on the opto board before replacing parts.

Fix

• Replace the emitter and receiver; MV8114 parts worked here.

Systems

• Sega/Stern Whitestar

Games

• Independence Day

Related tips

• Opto LED part numbers and replacing them in pairs
• Drained ball not seen, game stalls: VUK opto stuck closed, replace the transmitter

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