Quoted from insight75:
Can someone explain to me what the EOS switch on the flipper does on these machines (and all Sterns)? I realize mine wasn't set correctly and opening and I don't see a difference in performance of the flipper.
On Stern games (and all Sega, and later DE games with the TY-FFASI flipper board), the electronics re-kick the flipper (hard) when the EOS switch is opened and the flipper button is being held. That is, there's a timed initial hard kick, followed by the "hold" voltage; if the EOS switch indicates the flipper is not at the end of its stroke, the electronics will re-apply the oomph.
This fixes an issue where there's a kicker that fires the ball at the flipper (which is why they added this switch on DE Jurassic Park). If this switch is not working, a fast-moving ball will drop the flipper, and it will rise slowly if at all, because the electronics are only applying the hold voltage. (if I got the operation of the EOS switch backwards, my point stands, I just don't remember which state is normal.)
For all of the upper flippers on Simpsons, there is no EOS switch, and that's fine, since those flippers are not likely to get held up and face fast-moving balls.