Quoted from Vector:It sounds like you have a failing opto at the flipper button. When the soccer ball runs, the 12vdc goes low which makes the opto oscillate rapidly. This is what causes the weak flipper. It's very easy to confirm. While holding the flipper bat, press and hold the flipper button. You should feel a small pulse and then almost nothing. If the opto is bad, you will feel a continuous pull or buzzing at the flipper bat. You can also swap the left and right flipper button optos to see if the problem follows the opto or stays with the flipper. Sometimes the opto can be cleaned, but if that doesn't work, then it must be replaced.
Old thread but valuable! I'm experiencing exactly these symptoms. New optos ordered (only one flipper was acting up, but going to replace both).
Balt, MD
