The game reports a fault on the upper left flipper button switch even though the game has no upper flippers.

Upper left flipper button switch error on a two-flipper game: broken trace on opto board

Cause: Each flipper opto board has two optos even on two-flipper games; the left board's upper opto (used for lane change and entering initials) had a broken trace. This game reports that opto when it fails.

Checks

• Look at the left flipper opto board behind the flipper button for a cracked trace or failed opto.
• Swapping the left and right flipper opto boards shows whether the fault follows the board.

Fix

• Repair the broken trace or replace the opto (or the board). Jumpering the opto only clears the message for a while.

Systems

• WPC Fliptronics

Games

• Creature from the Black Lagoon

Related tips

• Creature from the Black Lagoon: "check switch F6 U.R. Flipper" error
• Flipper cabinet opto switch boards
• Game reports flipper EOS switches stuck closed when they aren't: reseat the ribbons
• Strange opto and switch faults: the manual swaps J4 and J6 on the opto board
• Testing optos in switch edge test
• Games that came with Type 1 flipper opto boards
• Where WPC games use opto switches
• Flipper buttons stop working but coils fire in test: Fliptronic board switch plugs

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