Quoted from emkay:
I guess I'm confuser'd what we're talking about. EOS switch is on or off, what does "flipper board control" change about that?
Whitestar flippers (including Simpsons) are controlled by electronics. When the button is pressed, the flipper kicks; then, the flipper is held up by electronics pulsing the flipper 12 times a second. If the EOS gets opened, the flipper gets pulsed back to the up position (full strength kick). This helps with things like the raptor kicker in Jurassic Park, but I've seen it happen on Simpsons, too.
Older games (pre-1990) used the EOS switch to control whether the flipper was held up with high or low power. If your EOS isn't working on these, it tends to melt the sleeve in the coil if the primary stays on too long, or not work at all or be super wimpy if the primary never engages. These aren't as simple or reliable as Stern flippers, but they don't tend to hum or chatter.
Data East added a flipper board around 1990, and Williams followed suit in 1992.