The upper right flipper flutters, buzzes loudly when held, loses power quickly and finally stops working. Coil solder joints and EOS look fine.

Upper flipper flutters, buzzes on hold and fades out: faulty flipper opto board

Cause: The flipper opto board for that flipper was faulty.

Checks

• Measure the coil windings to rule out the coil.
• Swap the flipper opto boards between sides to see if the fault moves.

Fix

• Replace the faulty flipper opto board.

Systems

• WPC Fliptronics

Games

• White Water

Related tips

• Upper flipper sometimes weak, then buttons dead after cleaning: replace the flipper optos
• Games that came with Type 1 flipper opto boards
• Upper right flipper chatters, follows the Fliptronic board: wrong U2 and a bad D2
• Flipper buttons stop working but coils fire in test: Fliptronic board switch plugs
• Fliptronics: flipper will not hold up (flutters)
• Fliptronics flipper does not work: test the flipper opto board
• Mount the flipper coil with its lugs away from the coil stop
• Flipper rebuild step 1: remove and check the coil stop

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