The lower right flipper looks normal when flipped empty, but it hits the ball weakly and gives way if you resist it with a finger. A full rebuild (coil, EOS, linkage, spring) and a new power driver transistor changed nothing.

One flipper weak after a full rebuild: dirty cabinet flipper opto

Cause: Dust on the cabinet flipper button opto. The switch input flutters on and off, so the flipper never gets a full-strength power stroke. A weak opto, or a bad LM339 comparator on the Fliptronic board that reads the optos, gives the same symptom.

Checks

• Swap the left and right cabinet opto boards (both must be plugged in) and see whether the weak side moves.
• Clean the slots of the opto switches on the button boards and test again.
• If the problem stays on the same side after the swap, look at the LM339 chips on the Fliptronic board.

Fix

• Clean the cabinet flipper opto boards. Replace the optos or the board if cleaning doesn't last.

Systems

• WPC-Security (WPC-S)

Games

• The Flintstones

Related tips

• Fliptronics flipper does not work: test the flipper opto board
• Fliptronics and WPC-95: weak flipper
• 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
• Flippers play fine but buttons do nothing in video mode or initials entry
• Flipper stays up briefly after the button is released
• Upper flipper switch reported bad on a game with no upper flipper

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