I have a Lethal Weapon 3 (Data East system 3) with a sticking flipper. When I press the left flipper button the flipper fires, but sticks up. The hold circuit stays energized after I release the button. It drops when I turn off the power so it's not a mechanical bind. I swapped the flipper PCB under the playfield with another one and it does the same thing. Which area/components of the driver board do I need to check? I also verified it's not a switch matrix issue (left flipper stops registering when I release the button which is normal).

Not sure I follow you, are you saying an open diode may have caused the 9v transistor on the driver board to fail?

Yep that was it. Diode fixed it. Thanks!