At power-on the game reports a fault on the upper right flipper switch (F6), though the game has no upper right flipper.

Creature from the Black Lagoon: "check switch F6 U.R. Flipper" error

Cause: Each flipper opto board carries a lower-flipper opto and an upper-flipper opto even on two-flipper games, and the game still checks the unused one, so a dirty unused opto gets flagged.

Checks

• Inspect the flipper opto board optos.

Fix

• Clean the optos with a cotton swab; replace the opto if that doesn't clear it.
• Or bridge connector pins 1 and 2 on the flipper opto board with solder, joining the S1 and S2 outputs so the good opto serves both inputs.

Systems

• WPC Fliptronics

Games

• Creature from the Black Lagoon

Related tips

• Upper flipper switch reported bad on a game with no upper flipper
• Upper left flipper button switch error on a two-flipper game: broken trace on opto board
• Upper flipper sometimes weak, then buttons dead after cleaning: replace the flipper optos
• Flipper cabinet opto switch boards
• Flipper stuck up but drops when the power goes off
• Fliptronics: flipper button does not register in switch test
• Fliptronics: flipper coil gets hot after a while of play
• Fliptronics and WPC-95: weak flipper

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